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{{#Wiki_filter:DRESDEN - UFSAR 6.0-1 6.0  ENGINEERED SAFETY FEATURES This Chapter is organized as follows: 
{{#Wiki_filter:}}
 
A. Section 6.0 - Identification of engineered safety features; B. Section 6.1 - Engineered safety feature materials; C. Section 6.2 - Containment systems;
 
D. Section 6.3 - Emergency core cooling systems; E. Section 6.4 - Habitability systems;
 
F. Section 6.5 - Fission produc t removal and control systems; and
 
G. Section 6.6 - Inservice inspection of Class 2 and 3 components.
 
===6.0 Identification===
of Engineered Safety Features Section 6.0 is the complete listing of engineered safety feature (ESF) systems, structures, and components. Discussion of a system, structure, or component elsewhere in Chapter 6 does not imply classification as an engineered safety feature. Conversely, systems listed in Section 6.0 but not described elsewhere in Chapter 6 are classified as ESFs, even though the detailed discussion of the system, structure, or component is in another UFSAR chapter.
 
This section describes the functional requirements and performance characteristics of the ESFs, which have been provided in addition to those safety features included in the design of the reactor, reactor coolant system,  reactor control systems, and other instrumentation or process systems described elsewhere in this report. These ESFs are included in the plant for the purpose of reducing the consequences of postulated accidents. The following ESFs have been provided:
A. Containment systems;
 
B. Emergency core cooling systems; C. Standby coolant supply system;
 
D. Main steam line flow restrictors; E. Control rod velocity limiter;
 
F. Control rod housing support;
 
G. Standby liquid control system; DRESDEN - UFSAR Rev. 4    6.0-2  H. Containment atmospheric control system; I. Reactor protection system; and
 
J. Isolation condenser.
 
====6.0.1 Containment====
Systems The containment systems consist of the primary containment system and the secondary containment system. The performance objectives of the primary containment system are to provide a barrier which, in the event of a loss-of-coolant accident (LOCA), will control the release of fission products to the secondary containment and to rapidly reduce the pressure in the containment resulting from a LOCA. The performance objectives of the secondary containment system are to minimize ground-level release of airborne radioactive materials and to provide for controlled, elevated release of the reactor building atmosphere under accident conditions through the use of the standby gas treatment system (SBGTS). The containment systems are described in Section 6.2. Section 15.6 discusses the LOCA.
The containment isolation system provides protection against the consequences of an accident involving the release of radioactive materials from the reactor coolant pressure boundary by automatically isolating fluid lines which penetrate the containment wall. Se ctions 6.2.4 and 7.3.2 contain a description of the primary containment isolation system. Section 6.2.3 describes the secondary containment system.
 
The SBGTS removes radioactive contamination from the air in the secondary containment using a high efficiency particulate air (HEPA) and an activated charcoal filter system. The air is then discharged to the environment through the 310-fo ot chimney. The SBGTS can also be manually aligned to treat the air inside the primary containment. The SBGTS is described in Section 6.5.
 
====6.0.2 Emergency====
Core Cooling System
 
The emergency core cooling system (ECCS) is automatically placed in operation whenever a loss-of-coolant condition is detected. The subsystems contained in the ECCS are the core spray, low pressure coolant injection (LPCI)/containment cooling, high pressure coolant injection (HPCI), and automatic depressurization (ADS) systems. The core spray and LPCI systems are designed for low-pressure operation, whereas the HPCI and ADS systems are designed for high-pressure operation. The containment cooling system is a separate function of the ECCS and is designed to remove heat from the containment, reduce the containment pr essure and restore suppression pool temperature following a LOCA. The containment cooling system is described in Section 6.2.2, the ECCS is described in Section 6.3, and the LOCA is discussed in Section 15.6.
DRESDEN - UFSAR Rev. 7  June 2007    6.0-3 6.0.3  Standby Coolant Supply System The standby coolant supply system is a crosstie between the station service water and the condenser hotwell of each unit. It supplies water to maintain feedwater flow to the reactor in the event the water is needed for core flooding or containment flooding following a postulated LOCA. The crosstie is supplied with double valves to minimize leakage of river water to the condenser. The system is manually operated from the control room. The standby coolant supply system is described in Section 9.2.8. The LOCA is discussed in Section 15.6.
 
6.0.4 Main Steam Line Flow Restrictors
 
The main steam line flow restrictor is a simple venturi, welded into each main steam line, for the purpose of limiting the steam discharge through a break in the steam line. The main steam line break accident is described in Section 15.6. A description of the main steam line flow restrictors is provided in Section 5.4.4.
 
====6.0.5 Control====
Rod Velocity Limiter
 
The control rod velocity limiter consists of two conical elements which restrict the downward fall of the control rod yet do not retard the upward motion of the control rod during scram. These conical elements have no moving parts and are attached to the control rod. A description of the control rod velocity limiter is provided in Section 4.6. The control rod drop accident is analyzed in Section
 
15.4.9. 
 
====6.0.6 Control====
Rod Housing Support
 
The control rod housing support is a gridwork located immediately below the control rod housings. Its purpose is to prevent control rod ejection should the control rod housing fail. A description of the control rod housing support is provided in Section 4.6.
 
====6.0.7 Standby====
Liquid Control System The standby liquid control (SBLC) system fulfills two performance objectives. First, it provides an additional and independent means of reactivity control and is capable of making and holding the reactor core subcritical from any hot standby or hot operating condition. The liquid control is a liquid boron solution which can be injected into the reactor vessel at pr essures above the vessel design pressure at a constant flowrate. A description of the standby liquid control system is provided in Section 9.3.5. Failure to s cram is discussed in Section 15.8.
Second, in the event of a design basis LOCA,  the contents of the SBLC system tanks are injected into the suppression pool to maintain the pH of the pool at a value greater than 7. This ensures that the particular iodine deposited into the pool during a DBA LOCA does not re-evolve and become airborne as elemental iodine. This role of th e SBLC system is described in UFSAR 15.6.5.5.
DRESDEN - UFSAR Rev. 7  June 2007    6.0-4 6.0.8 Containment Atmospheric Control The primary containment atmospheric control system consists of the vent, purge, and inerting system; the pumpback system, the nitrogen containment atmosphere dilution (NCAD) system; and the containment atmosphere monitoring system. The air dilution capability of the atmospheric containment atmosphere dilution (ACAD) system has been permanently disabled. The ACAD pressure bleed subsystem has been disabled and the piping has been cut and capped. The primary means of containment combustible gas control is the inerted containment. The pumpback system is not used for post-accident consequence mitigation and is not an ESF. Those portions of the CAM system and the vent, purge, and inerting system which are utilized for post-accident consequence mitigation are ESFs. The atmospheric control systems are described in Section 6.2.5, and the LOCA is analyzed in Section 15.6.
 
====6.0.9 Reactor====
Protection System
 
The reactor protection system (RPS) monitors reactor operation and initiates a reactor trip upon detection of an unsafe condition that might cause damage to the reactor fuel or result in the release of radioactive materials to the environment. It is designed to function following any design basis accident described in Chapter 15. The RPS is described in Section 7.2.
 
6.0.10 Isolation Condenser
 
The isolation condenser provides cooling for the reactor core when the reactor becomes isolated from the main condenser upon closure of the main steam isolation valves (MSIVs). Closure of the MSIVs can occur following a loss of offsite power, as described in Section 15.2. The isolation condenser is backed up by the HPCI system. It is described in Section 5.4.6.
 
DRESDEN - UFSAR Rev. 4    6.1-1 6.1 ENGINEERED SAFETY FEATURE MATERIALS
 
Materials used in the Dresden engineered safety feature (ESF) systems are required to withstand the environmental conditions encountered during normal operation and subsequent to any postulated accident requiring their operation. The selection of these materials is based on an engineering review and evaluation for compatibility with other materials to preclude interactions that could potentially impair the operation of the ESF systems.
 
Section 6.2.1.2.1.1 discusses materials used in the drywell expansion gap between the steel drywell liner and the concrete walls.
 
====6.1.1 Metallic====
Materials 6.1.1.1 Materials Selection and Fabrication Engineered safety feature systems and components have been evaluated for adequacy of the materials of fabrication. Since original plant design and construction, several codes and standards have been revised to incorporate the results of additional research.
Revised codes affecting material selection and fabrication are:
 
A. Fracture toughness, B. Quality group classification,    C. Code stress limits, D. Radiography requirements, and
 
E. Fatigue analysis of piping systems.
 
Changes in the areas of quality group classification, code stress limits, and fatigue analysis of piping systems were determined by the NRC to have little impact on the safety of ESF systems. However, since a radical change in the fracture toughness test requirements occurred in 1972, and since radiography requirements compared to available documentation of the inspections actually performed on certain components indicated a possible discrepancy, a reevaluation of associated components was performed. The results of this reevaluation are discussed below and tabulated in Table 6.1-1. Refer also to SEP TOPIC III-1:  Classification of Structures, Components, and Systems (Seismic and Quality) for a discussion of component radiography inspection requirements.
The original specifications indicate that the low pressure coolant injection (LPCI) pump casings, high pressure coolant injection (HPCI) pump casings, and core spray pu mp casings were built to ASME Section III, Class C. The 1965 edition of the code requires impact testing. Also, according to Table ND-2311-1 of the code, A216, Grade WCB would be exempt from impact testing if the material was quenched and tempered (ASME Section III allows heat treating but does not require it). The design temperature range of these pumps is 40
°F to 165°F, with normal operating DRESDEN - UFSAR Rev. 6  June 2005  6.1-2 temperature around 95
°F. Brittle fracture is not a problem in this moderate temperature range.
The original specification indicates that the LPCI heat exchangers (shell side) were built to ASME Section III, Class C. The 1965 edition of the code requires impact testing. Material specification A212 has been discontinued and replaced by A515, Grade 70. Fracture toughness at the minimum heat exchanger service temperature of 51
°F has been analyzed and shown to be adequate. Refer to Section 6.2.2.3.3 for additional details of this evaluation.
The HPCI drain and condensate line piping, fittings, and valves have 5/8-inch or less nominal wall thickness and are exempt from impact testing. The steam piping is over 6 inches in diameter and has a 5/8-inch or less nominal wall thickness with the lowest operating temperature exceeding 150
°F. This further exempts this system from impact testing according to ASME Section III, NC 2311a9.
Note that ASME Section III, 1965 edition, provided minimum construction requirements for vessels used in nuclear power plan ts. It classified pressure vessels as A, B, or C. Class A vessels are equivalent to Class 1 vessels of the current code.
Class B is concerned with containment vessels, and Class C is  concerned with vessels used in a nuclear power system not covered under Classes A or B. System classification is addressed in the Dresden Station Inservice Inspection (ISI) Plan. As noted in the plan, piping, pumps and valves were built primarily to the rules of USAS B31.1.1.0-1967, Power Piping. Consequently, the Dresden Station ISI Program does not contain any ASME Section III, Code Class 1, 2, or 3 systems. The ISI Program system classifications are based on Regulatory Guide 1.26, Revision 3,  and were developed for the sole purpose of assigning appropriate ISI requirements. The ISI Program is discussed further in Sections 5.2 and 6.6.
 
The LPCI and core spray pumps for Dresden are Class 2 components, as described in Regulatory Guide 1.26 under Group B quality standards. The code of construction and current classification of the pumps were verified by GE.
 
The DGCW and CCSW systems contain cast iron valves. Additionally, the CCSW pump casings are made of cast iron. Because the use of cast iron in safety-related systems was not evaluated at the time of the NRC Systematic Evaluation Program (SEP), cast iron was not addressed in the NRC Safety Evaluations regarding SEP Top III-1. Cast iron has lower ductility and fracture toughness than other materials typically used in safety-related piping systems. Although it is an acceptable material in the USAS B31.1-1967 code, there are no material specifications for cast iron that are acceptable in the 1977 ASME Section III Code, which formed the basis of the evaluation criteria of SEP Topic III-1. To accommodate the lower ductility and fracture toughness, cast iron valve bodies and pump casings in the DGCW and CCSW systems meet the acceptance criteria described in Section 3.9.3.1.3.5.1.
Confirmation that the atmospheric storage tanks meet current compressive stress requirements was requested by the NRC. In response to this request, it was found that the standby liquid control tank was designed and analyzed based on the methodology outlined in API-650 Code specifications. However, in 1982 the tank was requalified per the then current ASME Section III, Subsection ND. It was determined that the standby liquid control tank roof cover, vessel shell, base plate, roof ring, weldment, and U-bolts met the ASME Code requirements current in 1982. The analysis also showed that the actual stresses in these components subjected to specified seismic excitations are well within the ASME Section III allowables at the design temperature of 150
°F. Reflective Metal insulation (mirror type)  or nonmetallic insulation (Nukon Blanket, foam glass or closed cell foam plastic) installed on piping inside the containment meets the requirements as defined in Section 5.2.3.2.3, "Compatibility of Construction Materials with External Insulation and Reactor Coolant". Therefore, the potential for stress corrosion cracking due to the presence of leachable chlorides in nonmetallic thermal insulation is not a concern.
DRESDEN - UFSAR Rev. 4    6.1-3 6.1.1.2 Composition, Compatibility, and Stability of Containment and Core Spray Coolants
 
Dresden Station uses high-purity demineralized water in the reactor vessel and for post-accident containment spray and core spray. The torus also contains demineralized water.
All carbon steel surfaces in the torus are painted to prevent corrosion (see Section 6.1.2). Even without protective coatings, the expected corrosion rate for carbon steel, used structurally in air-saturated demineralized water, is less than 10 mils per year. Such a corrosion rate following an accident is of negligible significance.
 
In the unlikely event that the standby liquid control system were actuated after a loss-of-coolant accident (LOCA), sodium pentaborate solution would be introduced into the reactor vessel. If the vessel were refilled to the elevation of the break, the sodium pentaborate solution in the vessel would spill into the torus.
When sodium pentaborate dissolves in water, it produces a mildly basic solution. The pH of the solution varies with concentration. For the range of concentrations expected, the pH is between 7.4 and 7.8.[1]  At the maximum expected sodium pentaborate concentration during recirculation, carbon steel would corrode at a uniform rate of about 11 mils per year, and stainless steel at a rate of less than 0.1 mils per year. Again, these rates are insignificant following an accident. Thus, no additional provisions are required to control corrosion of steel following an accident.
Dresden relies primarily on inerting the containment atmosphere for post-accident hydrogen control. Control of post-accident chemistry to minimize the evolution of hydrogen from aluminum corrosion is therefore not a consideration in the Dresden design. Post-accident iodine control is accomplished through containment integrity, and operation of the standby gas treatment system. Containment spray additives, such as sodium hydroxide, are not used to remove radio-iodines from the containment atmosphere. Therefore, post-accident chemistry control to ensure the retention of iodines in sump water is not required.
 
Reactor water is sampled and analyzed for conductivity and chloride concentration every 72 hours during normal operation, to ensure that the conductivity and chloride concentration do not exceed 5
µmho/cm and 0.5 ppm, respectively. Water in the condensate storage tank is sampled 3 times a week, to ensure that the conductivity and chloride concentration do not exceed 1
µmho/cm and 0.01 ppm, respectively, and that the pH is between 5.6 and 8.6. The torus water is sampled monthly.
The NRC has determined that the use of demineralized water in the reactor vessel, post-accident containment spray, and core spray, in conjunction with the established periodic water sampling programs, provide reasonable assurance that the conductivity, pH, and chloride concentration of the water would be within the normal plant operating limits such that proper water chemistry can be maintained during the recirculation phase following a DBA consistent with the acceptance criteria of Standard Review Plan Section 6.1.1 for boiling water reactors.
DRESDEN - UFSAR Rev. 3    6.1-4 6.1.2 Organic Materials Identified coatings cover approximately 180,500 square feet of the interior of the Dresden containment. Approximately 58,950 square feet of this is in the drywell, and 121,550 square feet is in the torus.
 
The drywell shell, reactor shield wall, and vessel supports were originally coated with Dupont #67-4-746 Dulux Zinc Chromate Primer. This layer was covered with Carboline Rustbond Primer 6C Modified Vinyl. It was finished with Carboline Polyclad #933-1 Vinyl Copolymer. These two vinyls are described as a polyvinyl chloride. Failure of this type of material is at an exposure of 8.7 x 10 8 rads.[2]  The total integrated dose for coatings within a typical BWR containment ranges from 5 x 10 6 to 3 x 10 9 rads, with most surfaces seeing less than 10 7 rads.[3]  The normal integrated 40-year dose for Dresden is between 1.5 x 10 6 to 1.9 x 10 6 rads;[4] add this to a 1-year post-accident dose of 1.1 x 10 8 rad[5] and the total dose inside drywell would be 1.11 x 10 8 rads. It is, therefore, evident that this coating system would not fail due to radiation effects following an accident.
Other components of the drywell, which are coated with different materials, would not fail due to radiation effects following an accident. The concrete surfaces are coated with Carboline 195 Surfacer, a modified epoxy-polyamide, and Carboline Phenoline 368 WG Finish, a modified phenolic. The maximum gamma radiation resistance of an epoxy is approximately 4 x 10 8 to 9 x 10 8 rads, while that of phenolic coatings is 4.4 x 10 9 rads. The structural steel framing and lateral bracing are covered with the above named Dupont primer, an intermediate coating of alkyd enamel, and a finish of Detroit Graphite Red Lead 501 Alkyd Enamel. The grating areas are covered with the Dupont Zinc Chromate and finished with the Alkyd Enamel. The maximum gamma radiation resistance for an Alkyd Enamel is 5.7 x 10 9 rads. As compared to the values listed in Section 6.1.3, Reference 3, it may be deduced that this system would not fail following an accident.
 
The design temperature for the Dresden containment is 281
°F for a design basis accident (DBA) and 135°F during normal power operation (see Section 6.2.1). The manufacturer's data lists the vinyls' main temperature resistance at approximately 150
°F and the phenolics at 200
°F - 250°F. This low temperature resistance in the vinyl materials is causing some peeling in the upper level of the drywell. The material has never dropped off, and the peelings are smaller than 1 square inch. Also, pull tests show pulls were greater than 200 pounds, as stated in the ANSI N5.12 report. This problem is controlled by removing the loose coatings, performing the proper surface preparation and touching up the degraded areas with coatings that are DBA qualified to ANSI N101.2, N101.4 and N5.12 requirements. These products shall be evaluated for chemical resistance, decontaminability, radiation tolerance and exposure to DBA conditions. Failure is not expected with these products (except in the immediate area of a line break) as evidenced by DBA test re sults for these coatings under LOCA conditions. For touch-up work in the torus, coatings that are DBA qualified to ANSI N101.2, N101.4 and N5.12 requirements shall also be used.
Since the ESF fluids are not taken from the sump in the Mark I design, it is unlikely that any peeling of the vinyl paint on drywell surfaces would lead to significant safety problems. The sump at the bottom of the drywell acts as a drain which is valved off during the DBA. The containment and core sprays during a DBA take suction from the bottom of the suppression pool. Any peeling vinyl paint flakes would collect in the bottom of the drywell where they would not interfere DRESDEN - UFSAR 6.1-5 with the coolant recirculation during a DBA. Taking into account these features of the Mark I design, there is reasonable assurance that any peeling of the vinyl paints in the DBA environment would not interfere with the operation of the engineered safety features.
 
The two main safety concerns that the torus intern al coating systems must address are as follows:
A. That the coating materials remain adherent and do not fall off in sufficient quantities under DBA conditions so as to adversely affect the operation of engineered safety
 
systems, and B. That the coating system effectively prevents degradation (e.g., corrosion) of the containment systems themselves under normal operating conditions.
The original coating system applied to the Unit 2 torus in January 1968 was Phenolic 368 manufactured by the Carboline Company. The portion of the coating system below the waterline (immersion phase) failed by gross intercoat delamination early in its lifetime and was replaced with the Carbo Zinc 11 inorganic zinc primer (also manufactured by Carboline). This system failed within
 
2 1/2 years because of insufficient coating thickness at the time of first application (the zinc was cathodically sacrificed). Subsequently, a new application of Carbo Zinc 11 with adequate thickness was applied in January of 1975. Meanwhile, the vapor phase of the system (above the waterline) aged rather poorly and by 1984 was described as showing 3 to 10% pinpoint rusting throughout. Abrasive blast cleaning and total recoating of th e torus internals was performed during the D2R11 outage using a new epoxy coating (the 6548/7107 system manufactured by the Keeler and Long Company was installed). In addition, a "holiday" (sponge) test was performed to detect and fix all pin holes that may have existed in the new coating. The total dry film thickness falls within the coating's qualified thickness range. Thus, the coating is likely to perform as expected of a service level Class I coating system.
 
The old epoxy/modified phenolic coating remains on most of the vent system components. Although most of the vent system is in the vapor phase of the torus, half of the downcomers have this old coating below the waterline on their interior surfaces.
 
The original Phenolic 368 coating system was applied to the Unit 3 torus in June of 1968. The vapor phase failed by pinpoint rusting after about 16 years of service.
In the immersion phase, gross failure similar to that at Unit 2 was detected and the Carbo Zinc 11 primer was applied. Again the inorganic zinc was deemed unserviceable after only two 1-year cycles of operation. In May of 1975, five different coating systems were applied (three phenolic and two epoxy) to determine which of the systems would provide the best service when exposed to the actual torus environment. The test results showed that the Plasite 7155H and Carboline 368 systems failed, but the Carbo Zinc 11, Mobil 78 epoxy, and Keeler and Long 7107/7500/7475 epoxy system performed satisfactorily. The Keeler and Long system developed some blisters but these were observed to be associated with the 7475 finish coat only and were probably due to application problems. The test period was approximately 10 years. Subsequently, a total abrasive blast cleaning and recoat was performed during the D3R10 outage.
DRESDEN - UFSAR 6.1-6 Additionally, Carbon Zinc 11 SG was used to coat the safety relief valve (SRV) lines and T-quencher frames.
The painting systems, both in the drywell and in the torus, are inspected and repaired as necessary during each refueling outage. Evaluation of coating integrity is conducted in accordance with the requirements of ANSI N101.2-1972, Section 4.5. The chemical, temperature, and radiation resistance of the current coating systems, together with periodic inspection and maintenance, make the possibility of torus strainer clogging due to coating failure after an accident, remote. Refer to Section 6.2.2.3.2 for an analysis of the potential effects of torus water contamination by debris.
Very small amounts of gas are evolved when aromatic organic compounds of the type found in radiation-resistant plastic are irradiated. For example, a phenolic plastic irradiated to a dose of 10 9 rads produced 3 milliliters (STP) of gas per gram of plastic.
[2]  For the approximately 150 cubic feet of organic coating existing in the containment, approximately 90 cubic feet of gas would be generated for the conservatively estimated DBA dose of 10 8 rads. The gas is mostly hydrogen and carbon dioxide, and less than a tenth of it is volatile organic compounds. The presence of small amounts of organic gases in containment after a DBA would not interfere with the adsorption of organic iodides by the purge charcoal filters.
The amount of hydrogen from this source is small compared to that which could be produced in a DBA from the zirconium-water reaction, from the radiolysis of water, or from the reaction of the zinc in inorganic zinc coatings with high-temperature borate solutions.
[6]
DRESDEN - UFSAR 6.1-7 6.1.3 References
: 1. U.S. Borax Industrial Products Catalog, p. 65, n.d., figure titled, "pH Values in the System Na 2 O-B 2 O 3-H 2O at 25°C." 
: 2. Bolt and Carrol, Radiation Effects on Organic Materials, Academic Press, New York 1963.
: 3. American National Standards Institute, ANSI N101.2-1972, "Protective Coatings (Paints) for Light Water Nuclear Reactor Containment Facilities." 
: 4. "Environmental Qualification of Electrical Equipment Dresden Nuclear Power Station Unit 2," Bechtel Power Corporation, November 1, 1980, Volume 3 of 3.
: 5. Response to IE Bulletin 79-01B Post-LOCA/HELB Radiation Exposure Levels Received by ESF Components for Dresden Nuclear Power Station Units 2 and 3, Bechtel Power Corporation, July 18, 1980.
: 6. Zittel, H.E, "Post-Accident Hydrogen Generation from Protective Coatings in Power Reactors," Nuclear Technology 17, pp. 143-146, 1973.
 
DRESDEN - UFSAR        Rev. 4 (Sheet 1 of 7)
Table 6.1-1 FRACTURE TOUGHNESS REQUIREMENTS Structures, Systems, and Components Quality GroupClassification(1) Material Impact TestRequired? Reason for Exemption(2) Remarks      Recirculation System      Recirculation system piping Class A Type 304 stainless steel(5) No 8e  Recirculation system valves Class A ASTM A351, Gr. CF8M stainless steel No 8e  Recirculation system pumps Class A Type 304, 316 stainless steel No 8e Emergency Systems      Isolation Condenser      Shell side Class C ASTM A106, Gr. B carbon steel No 8a  Tube side Class B Type 304, 316 stainless steel No 8e All stainless steel piping, valves, fittings Class B Type 304(6)  No 8e  All carbon steel piping 
 
Class B  ASTM A106, Gr. B No  8a Fittings and Valves Class B carbon steel  No 8a        Standby Liquid Control System Pump casing Class B Carbon steel No 8d  Tank Class B Type 304 stainless steel No 8e Piping Class B Type 304 stainless steel No  8d, e 
 
DRESDEN - UFSAR        Rev. 6 June 2005 (Sheet 2 of 7)
Table 6.1-1 (Continued)
FRACTURE TOUGHNESS REQUIREMENTS Structures, Systems, and Components Quality Group Classification(1) Material Impact TestRequired? Reason for Exemption(2) Remarks      Core Spray System      Pump casing Class B ASTM A216, Gr. WCB carbon steel Yes  Thickness up to 13/16 in. All carbon steel piping Valves and fittings Class B  Class B ASTM A106, Gr. B(7)  carbon steel No  No  8a  8a All stainless steel piping, fittings, valves Class B Type 304 No 8a, e  Spray spargers and spray nozzles Class B Type 304 stainless steel No 8e        Low Pressure Coolant Injection
 
Pump casing Class B ASTM A216, Gr. WCB carbon steel Yes  Thickness up to 13/16 in.
All Stainless steel piping, fittings, valves Class B Type 304(9) No 8e  All carbon steel piping Valves and fittings Class B  Class B ASTM A106, Gr. B carbon  steel No  No 8a  8a    Containment Cooling Service Water Pump Casing All Carbon steel piping Carbon steel valves and fittings Cast iron valves Class C Class C Class C Class C  ASTM A126, Class B ASTM A106, Gr. B carbon steel ASTM A126, Class B No No No No  8a 8a 8a 8a DRESDEN - UFSAR        Rev. 4 (Sheet 3 of 7)
Table 6.1-1 (Continued)
FRACTURE TOUGHNESS REQUIREMENTS Structures, Systems, and Components Quality Group Classification(1) Material Impact Test Required?Reason for Exemption (2)  Remarks      Heat exchangers:      tube side Class B 70/30 CuNi(8) No 8f  shell side Class C ASTM A212, Gr. B carbon steel Yes  Portions have 1-in.
thickness High Pressure Coolant Injection Pump casing Class B ASTM A216, Gr. WCB carbon steel Yes  Thickness up to 1 1/2 in. Piping  Fittings, and valves Class B  Class B ASTM A106, Gr. B carbon steel  carbon steel No  No (8a, d)(3)  8a Impact test on all piping with nominal pipe diameter greater than 6 in. Spargers (feedwater spargers used) Class B Austenitic stainless steel No 8e Standby Coolant Supply System (condenser hotwell to service water line) Pipings, fittings, and valves Not safety-related  Deleted DRESDEN - UFSAR        Rev. 2 (Sheet 4 of 7)
Table 6.1-1 (Continued)
FRACTURE TOUGHNESS REQUIREMENTS Structures, Systems, and Components Quality Group Classification(1) Material Impact TestRequired? Reason for Exemption(2) Remarks      Standby Gas Treatment System Pipings fittings, and valves Class B Class B ASTM A106, Gr. B, ASTM A211Carbon steel, No No 8a  8a        Primary Containment      Safety valves Class A Carbon steel No 8d  Relief valves Class A Carbon steel No 8d        Containment Penetrations      Hydraulic lines to the control rod drives Class B Stainless steel No 8d  Valves Class B  No 8d        Containment Isolation Valves Not Listed with Major System Class A No  8d Control Rod Drive Housing Class A  No 8d DRESDEN - UFSAR        Rev. 4 (Sheet 5 of 7)
Table 6.1-1 (Continued)
FRACTURE TOUGHNESS REQUIREMENTS Structures, Systems, and Components Quality Group Classification(1) Material Impact TestRequired? Reason for Exemption(2) Remarks      Control Rod Drive System      Velocity limiter Class B Stainless steel casting No 8d  Guide tubes Class B Type 304 stainless steel No 8e Spent Fuel Storage Facilities      Spent fuel pool Class C Stainless steel lining (3/16-in. thick) No 8a Reactor Vessel Head Cooling System Piping, fittings, and valves Class C Stainless steel(10)  No 8d, e 
 
DRESDEN - UFSAR        Rev. 5 January 2003 (Sheet 6 of 7)
Table 6.1-1 (Continued)
FRACTURE TOUGHNESS REQUIREMENTS Structures, Systems, and Components Quality Group Classification(1)  Material Impact TestRequired? Reason for Exemption(2) Remarks      Condensate Feedwater System Piping from reactor vessel to outermost containment isolation valve Class A ASTM A106, Gr. B carbon steel No LST > 150F Thickness varies from 1.000-1.375 in.
Valves and fittings
 
Class A  Carbon steel No  LST > 150F  Main Steam System      Piping  Valves and fittings Class A  Class A ASTM A106, Gr. B Carbon steel No  No LST > 150F LST > 150FThickness 1.031 in.      Condensate Storage Tank Class C Aluminum No 8f Compressed Air System      Piping, fittings, and valves Class D  No 8d 
 
DRESDEN - UFSAR  Rev. 6  June 2005 (Sheet 7 of 7)
Table 6.1-1 (Continued)
FRACTURE TOUGHNESS REQUIREMENTS Structures, Systems, and Components Quality Group Classification(1)  Material Impact TestRequired? Reason for Exemption(2) Remarks      Standby Diesel-Generator System Service water piping Class C ASTM A106, Gr. B No 8a  Carbon steel valves and fittings Class C Carbon steel No 8a  Cast iron valves Class C ASTM A126, Class B No 8a  Fuel oil piping
 
Valves and fittings Class C Class C ASTM A53, Gr. B  Carbon steel No No 8a 8a Notes:  1. The quality group classification given here is the Regulatory Guide 1.26 classification to determine fracture toughness test ing requirements and should not be confused with safety classification. Refer to Section 3.2 for a discussion of safety classifica tions. 2. Refer to Tables A4 A4-6 of Appendix A in Franklin Research Center report on quality group classification of components a nd systems for explanation of exemptions. 3. Applies to drain and condensate piping. 4. For piping 2" and under, ASTM A335 Grade P11 or P22 may be substituted for ASTM A106 Grade B material for the same schedule. For fittings and valves 2" and under, ASTM A182 Grad e F11 or F22 may be substituted for ASTM A105 for the same rating. Substitutions are allowed up to a maximum temperature of 450
°F (operating or design) and apply to non-safety related piping and fittings only. No generic substitution of safety related piping/fittings is allowed. 5. Piping replacement on Unit 3 changed the piping material to type 316 stainless steel. 6. A portion of the Unit 3 isolation condenser retu rn line was replaced with type 316 stainless steel. 7. A portion of the piping from outboard valves 2-1402-24A/B to the reactor vessel safe end (Unit 2) was replaced with carbon s teel SA333, grade 6 under M12-2-75-39. 8. Some of the CCHX tubes have been replaced by A1-6XN alloy tubes. 9. A portion of the LPCI discharge, inboard from the outboard isolation valve, was replaced with type 316 (special chemistry) stainless steel. 10. A portion of the system is fabricated from A106, grade B carbon steel. 11. Material type A106, grade B is the preferred material with A53, grade B as an a cceptable substitute when A106 is not availa ble. 
 
DRESDEN - UFSAR Rev.8 June 2009 6.4-1 6.4 HABITABILITY SYSTEMS Habitability systems are provided to ensure that control room operators are able to remain in the control room, operate the plant safely under normal conditions, and maintain the plant in a safe condition under accident conditions. The worst-case design basis accident (DBA) for habitability considerations is postulated as a loss-of-coolant accident (LOCA) with main steam isolation valve leakage at Technical Specification limits. The control room is included in the control room envelope (CRE) as described in Section 6.4.2.1.
 
The habitability systems consist of systems and equipment which protect the control room operators against such postulated releases as radioactive materials, toxic gases, and smoke. Detailed descriptions of the various habitability provisions are discussed in other sections of the UFSAR, as stated below:
A. Tornado protection is addressed in Section 3.3;
 
B. Flood protection is discussed in Section 3.4; C. Lighting systems are described in Section 9.5.3; D. Protection against dynamic effects associated with the postulated rupture of piping is addressed in Section 3.6; and
 
E. Plant communication systems are described in Section 9.5.2.
 
====6.4.1 Design====
Basis
 
The control room and its supporting systems are designed to ensure that doses to its occupants do not exceed the limits of 10 CFR 50.67 and GDC 19. The supporting radiological analysis is done in accordance with USNRC Regulatory Guide 1.183.
 
====6.4.2 System====
Design
 
The Dresden Station has the following capabilities to ensure habitability of the control room envelope (CRE) under accident conditions:
A. The control room heating, ventilation, and air conditioning (HVAC) systems are capable of maintaining the control room atmosphere suitable for occupancy throughout the duration of a DBA.
B. The control room area contains food, adequate water and sanitary facilities. All these are available within the control room envelope (CRE). A supply of potassium iodide is available in the plant.
DRESDEN - UFSAR Rev. 8  June 2009    6.4-2    C. The HVAC systems are capable of detecting and protecting control room personnel from radioactive contamination or smoke released to the atmosphere.
 
D. Emergency breathing air, supplied by a bottled air reservoir or by self-contained air packs, is provided to protect control room personnel from exposure to contaminated air.
 
E. The HVAC system Train A is capable of manual transfer from the normal operating mode to the smoke purge mode. The HVAC systems are capable of manual transfer from the normal operating mode to the isolation/pressurization or isolation/recirculation modes. Emergency monitors and control room equipment are provided as necessary to ensure this capability, as described in Sections 6.4.4.1, 6.
4.4.2, and 6.4.4.3.
The control room is a Class I structure. Seismic design is addressed in Section 3.7. Seismic qualification of instruments and electrical equipment is addressed in Section 3.10. Missile protection is addressed in Section 3.5.
 
6.4.2.1 Definition of Control Room Envelope
 
SRP 6.4 provides guidance for defining the boundaries for a control room envelope. Within this zone, the plant operators are adequately protected against the effects of accidental radioactive gas releases. This zone also allows the control room to be maintained as the center from which emergency teams can safely operate during a design basis radiological release. To accomplish this, the following areas are included in the envelope:
 
A. Main control room for Units 1, 2, and 3, which includes kitchen, toilet, and locker rooms;
 
B. Train B HVAC equipment room.
 
Areas outside the CRE are isolated in emergency conditions. Support rooms such as the Shift Manager's  office are accessible to operators with the aid of breathing equipment. The auxiliary computer room is permanently isolated from the CRE. The Train A HVAC equipment room,  the auxiliary electrical equipment room, and the auxiliary computer room are not included in the CRE. The boundaries of the CRE are shown on Figure 6.4-1.
Figure 6.4-2 shows the arrangement of equipment in the control room and points of entry. Figure 6.4-3 is a plan view showing the location of radioactive material release points and control room air inlets.
DRESDEN - UFSAR Rev. 8 June 2009 6.4-3 6.4.2.2 Ventilation System Design The HVAC equipment described in this section is also discussed in Section 9.4.1, which explains normal use of the equipment. This section addresses emergency service requirements and the response and operation of control room HVAC equipment under emergency conditions. The control room HVAC system is shown in the control room HVAC P&IDs:  Drawings M-273, Sheet 1 and 2, and Drawing M-3121.
 
The control room HVAC system consists of a Train A HVAC system, a Train B HVAC system, an air filtration unit, and a smoke detection system. The multizone Train A system is the primary train for the control room envelope. Since Train A is used primarily during normal operations, it is described in Section 9.4.
The Train B HVAC system is a single zone system which provides the necessary cooling required in case of failure of the Train A system. The discharge air from the air handling unit (AHU) is divided into two zones, zone 1 is ducted to the control room and zone 2 is ducted to the Train B HVAC equipment room . The air distribution from each train is aligned through the use of air-operated isolation dampers. These dampers fail to the Train B mode since this train is powered from the emergency bus during a loss of offsite power (LOOP). The Train B AHU contains a centrifugal supply air fan, a direct-expansion cooling coil, and a medium-efficiency filter bank.
Train B provides cooling through the use of a reciprocating compressor and direct-expansion cooling coil. The condensing unit is normally cooled with the service wate r system. Howeve r, upon loss of service water, the condenser may be cooled with the containment cooling service water (CCSW) system. The CCSW supply to the refrigerant condenser can be drawn from either loop of the Unit 2 CCSW system. Refer to Section 9.2.1.2 for a description of the CCSW system.
The air filtration unit (AFU) complies with Regulatory Guide 1.52 and is located in the Train B HVAC equipment room. 
 
The Train A makeup air intake and exhaust dampers are bubble tight, with an area of 25 square feet each. The isolation dampers for the AFU bypass intake, kitchen and locker room/toilet exhaust ducts are leak tight. Isolation of the normal makeup air intake takes approximately 20 seconds.
6.4.2.3 Leak-Tightness The infiltration of unfiltered air into the control room emergency zone occurs through three different paths:
A. Through the emergency zone boundary; DRESDEN - UFSAR Rev. 8    June 2009 6.4-4  B. Through the system components located outside the emergency zone; and 
 
C. Through backflow at the zone boundary doors as a result of ingress or egress to or from the emergency zone.
 
Using the guidance of SRP 6.4, the infiltration through the emergency zone boundary is assumed to be zero when the system is in the isolation/pressurization mode. During emergency pressurized modes of operation, the control room ventilation system supplies 2000 ft 3/min (standard) of outdoor air to maintain the control room at 1/8-in.H 2O positive pressure with respect to the adjacent areas. Intentionally admitting outdoor air into the emergency zone prevents infiltration through the emergency zone boundary by assuring that air is exfiltrating from the zone at an adequate velocity (a velocity through the emergency zone boundary penetrations of approximately 1400 ft/min is required to develop a backpressure of 1/8-in.H 2 O). During the isolation/recirculation mode, infiltration through the emergency zone boundary is initially negligible because the control room will be at a positive pressure at the time of system isolation. 
 
In support of the full implementation of Alternate Source Term (AST) as described in and in accordance with the guidance of Regulatory Guide 1.183, Alternate Source Term (AST) radiological consequence analyses are performed for calculation of offsite and control room personnel Total Effective Dose Equivalent (TEDE) doses. Radiological consequences of infiltration are included in the radiological assessment addressed in USFAR 15.6.5.5. The ductwork and components under negative pressure and located outside the control room envelope are shown on Figure 6.4.1.
The infiltration analysis resulted in a total unfiltered infiltration rate of 263 ft 3/min (standard). The ductwork and components that are under a negative pressure and are located outside the emergency zone are shown on Figure 6.4-1. This figure also shows the leakage flowrate through the various components. A breakdown of the infiltration through the different leakage paths as is currently measured is shown in Table 6.4-1. Radiological consequences of infiltration are included in the radiological assessment addressed in UFSAR Section 15.6.5.5.2.
 
DRESDEN - UFSAR Rev.8    June 2009 6.4-5 6.4.2.4 Interaction with Other Zones and Pressure-Containing Equipment Potential adverse interactions between the control room emergency zone and adjacent zones that may allow the transfer of toxic or radioactive gases into the control room are minimized by maintaining the control room at a positive pressure of 1/8-in.H 2O during the isolation pressurization mode, with respect to adjacent areas. In addition, both the intake dampers and the dampers which isolate the emergency zone are automatically isolated or actuated by the operator in response to the odor of toxic gas or the reactor building ventilation system high radiation alarm.
 
Steam lines are not routed in the vicinity of an y control room wall. Pressurized breathing air cylinders are located above the control room.
 
6.4.2.5 Shielding Design The control room design consists of poured-in-place reinforced concrete with 6-inch floor and ceiling slabs and 18- to 27-inch walls. The radiation stre aming effect in the control room is considered negligible during normal operation and provides 30-day integrated dose post-LOCA as considered in section 15.6.5. This dose estimate is expected to increase by 19% following extended power uprate. Further details of the design of the control room shielding are contained in Section 12.3.2.2.4. Figures 12.3-1 through 12.3-5 illustrate the relative location of the control room and radiation sources and show the paths and shield thicknesses.
 
====6.4.3 System====
Operational Procedures For normal conditions, the Train A HV AC system operates as discussed in Section 9.4.1. If desired, Train B can be used for normal plant operations. Outside air is supplied to Train B by the AHU fan in this operating mode. Upon failure of the operating HVAC system train, that train is isolated and the redundant train is energized.
The control room HVAC system has three emergency modes:
 
A. The isolation/pressurization mode protects the control room personnel from airborne radioactive contaminants. In this mode, the normal outside air intakes are isolated, and the AFU provides makeup air to maintain pressurization. This mode is described more fully in Section 6.4.4.1.
 
B. The isolation/recirculation mode protects personnel from toxic gases. In this mode, all outside air intakes are isolated, and the control room air is recirculated through the operating HVAC train. This mode is described more fully in Section 6.4.4.2.
C. The smoke purge mode protects personnel from fire and smoke. In this mode, the Train A control room HVAC System exhausts 100% of the control room envelope air and replaces it with 100% outside air. This mode is described more fully in Section 6.4.4.3.
DRESDEN - UFSAR Rev. 8  June 2009    6.4-6 6.4.4 Design Evaluations This section evaluates the effectiveness of the HVAC system design in protecting the control room personnel from the postulated hazards of radioactive material, toxic gases, and smoke contaminating the control room atmosphere.
 
6.4.4.1 Radiation Protection
 
The control room HVAC system provides radiation protection by pressurizing the control room emergency zone with filtered air, isolating the normal outdoor air intakes, and isolating the kitchen and locker room exhaust fan dampers. This zone isolation with a filtered pressurization air-type system provides radiation protection by minimizing the infiltration of unfiltered air into the control room emergency zone. A positive pressure of 1/8-in.H 2O with respect to adjacent areas is maintained by passing 2000 ft 3/min of outdoor air through a HEPA filter unit tested and maintained in accordance with Technical Specification 5.5.7, Ventilation Filter Testing Program. The filter unit, booster fans, and associated controls are powered from the emergency bus. 
 
Radiation protection is provided to allow control room access and occupancy for the duration of a DBA. Satisfactory protection is provided based on isolating and pressurizing the control room emergency zone with filtered outdoor air no later than 40 minutes after radiation has been detected in the reactor building ventilation manifolds. 
 
Operator action is required within the time limit specified above to isolate the control room emergency zone and to activate the air filter unit. Isolation consists of closing the outdoor air intakes for both the Train A and B systems and closing the kitchen and locker room exhaust isolation dampers. Additionally, the exhaust fans are tripped from limit switches on the isolation dampers, thereby preventing the induction of unfiltered air into the control room via the exhaust duct. In the event of a LOOP or loss of instrument air, the isolation dampers fail to the isolation/pressurization mode. However, the pneumatic AFU booster fan discharge dampers also fail closed, thereby requiring manual operation prior to activating the booster fans during loss of instrument air. This failure mode is required to protect the emergency zone from a toxic chemical release during a loss of instrument air.
Section 15.6.5.5 contains an evaluation of the maximum expected dose to the control room during a DBA LOCA. The present analysis utilizes the Alternative Source Term (AST) methodology and conforms to USNRC Regulatory Guide 1.183. The resulting doses are within the limits of 10 CFR 50.67.
DRESDEN - UFSAR Rev. 4    6.4-6a 6.4.4.2 Toxic Gas Protection The control room HVAC system does not provide automatic toxic gas protection to the control room emergency zone in case of either an onsite or offsite toxic chemical accident. The results of the toxic chemical survey are provided in Section 2.2.3. An analysis of survey results was carried out to conform to Regulatory Guide 1.78, which discusses the requirements and guidelines to be used for determining the toxicity of chemicals in the control room following a postulated accident. The guidelines for DRESDEN - UFSAR 6.4-7 determining the toxicity of a given chemical include quantity, shipment frequencies, distance from source to site, and general properties of the chem ical such as vapor pressure and toxicity limits.
6.4.4.2.1 Analysis Assumptions Three types of standard limits are considered in defining toxicity. The first limit is the toxicity limit, which is the maximum concentration that can be tolerated for 2 minutes without physical incapacitation of an average human. If the toxicity limit is not available for a given chemical, other limits, called the short-term exposure limit (STEL), or the threshold limit value (TLV), are used. STEL is defined as the maximum concentration to which workers can be exposed for 15 minutes without suffering from irritation, tissue damage, narcosis leading to accident proneness, or reduction of work efficiency. The TLV is defined as the concentration below which a worker may be exposed 8 hours per day, 5 days per week without adverse health effects. These limits are taken from Regulatory Guide 1.78 and References 1 and 2.
Based on the toxicity guidelines given in Regulatory Guide 1.78, compounds were screened based on toxicity, quantity, and distance from source to the Dresden Station control room air intake to determine if air dispersion modeling would be required to determine the potential concentration of each compound in the control room.
 
For the initial screening of compounds, spill, release, and air dispersion models were selected from version 1.0 of a software program entitled Automated Resource for Chemical Hazard Incident Evaluation (ARCHIE) prepared by the Federal Emergency Management Agency.
[3] Flash calculations for subcooled gases or superheated liquids are taken from Reference 4. The concentration rise in the control room was calculated from NUREG-0570.
The models include a consideration of the following assumptions:
 
A. Chemicals in the analysis include:
: 1. Chemicals listed in Regulatory Guide 1.78, Table C-1;
: 2. Chemicals included in the original Control Room Habitability Study
[5] and found to be still present in greater than threshold quantities; and
: 3. Chemicals identified as being stored onsite at Dresden Station.
B. Threshold quantities for chemicals included in the analysis include:
: 1. Highway shipments - 10 tank trucks per year;
: 2. Rail shipments - 30 tank cars per year;
: 3. Barge shipments - 50 barges per year;
: 4. Onsite chemicals - greater than 100 pounds stored in a singe container; and DRESDEN - UFSAR 6.4-8    5. Offsite facilities - threshold quantities determined via procedure given in Regulatory Guide 1.78.
C. There is a failure of one container of toxic chemicals being shipped on a barge, tank car, or tank truck releasing all of its contents to the surroundings. Instantaneously, a puff of that fraction of chemical which would flash to a ga s at atmospheric pressure is released. The remaining chemical is assumed to spread uniformly on the ground and boil or evaporate as a function of time due to the heat acquired from the sun, ground, and surroundings. Further, no losses of chemicals are assumed to occur as a result of absorption into the ground, cleanup operations, or chemical reactions.
 
D. A spill from a railroad tank car is assumed to spread roughly over a circular area. Similarly, a spill occurring in the highways is also assumed to spread over a circular area.
 
E. The initial puff due to flashing, as well as the continuous plume due to evaporation, is transported and diluted by the wind to impact on the control room inlet. The atmospheric dilution factors are calculated based on the methodology of Regulatory Guide 1.78 and NUREG-0570.
 
F. Modeling is based on maximum concentration chemical accidents for offsite releases. Maximum concentration-duration chemical accidents were not considered due to an inability to obtain information on safety relief valves. It is believed that maximum concentration chemical release will provide conservative worst case accident scenarios as compared to maximum concentration-duration chemical releases.
G. To determine which chemicals need monitoring, the control room ventilation systems were assumed to continue normal operation for the analysis. The chemical concentrations as a function of time were calculated and the maximum levels determined. These were compared to the toxicity limits. Wherever the toxicity limits were not available, STEL values, or TLVs were used in lieu of toxicity limits.
 
H. When the concentration in the control room does not exceed the toxicity limit within 2 minutes after detection by odor, operator action to isolate the control room was assumed.
Wherever the toxicity limits were not available, STEL values, or TLVs were used in lieu of toxicity limits.
 
The control room outdoor concentration is calculated for each compound studied using the atmospheric dispersion model. The control room indoor concentration is computed from the outdoor concentration and the control room air exchange rate. Both concentrations, outdoor and indoor, are functions of time for specific meteorological conditions.
The chemical concentration inside the control room reaches the odor detection limit at time t 1 minutes. The chemical concentration inside the control room continues to build up to the toxicity limit at time t 2 minutes. The time required for buildup of a hazardous chemical from the odor detection concentration to the toxicity limit inside the control room is calculated as (t 2 - t 1) minutes. In Regulatory Guide 1.78, 2 minutes is considered sufficient time for a trained operator to put self-contained breathing apparatus (SCBA) into operation. The estimated time (t 2 - t 1) is DRESDEN - UFSAR 6.4-9 compared against the 2 minutes. If the time (t 2 - t 1) is less than 2 minutes, it means that the operator would not have sufficient time to put a SCBA on. In this case the control room is considered to become uninhabitable during the chemical release under specific meteorological conditions.
The air dispersion model included in the ARCHIE software calculates peak concentration of compounds at the control room air intake. The time required for buildup of a chemical from odor detection to the toxicity limit was calculated using this peak concentration. Using this calculation procedure a list of compounds was put together where (t 2 - t 1) was less than 2 minutes. These compounds were then studied in more detail using an air dispersion model following Regulatory Guide 1.78 methodology which factors in the time dependance of concentration at the control room air intake. This model gives a more accurate estimation of potential control room concentrations than the ARCHIE software which overestimates these concentrations.
 
6.4.4.2.2 Analysis Results
 
The onsite chemicals listed in Table 2.2-7 were screened and analyzed
[6] to determine if the release of any of those chemicals could pose a threat to control room habitability. The screening shows that none of the chemicals stored onsite pose a threat.
 
The offsite chemicals considered include the chemicals listed in Regulatory Guide 1.78, along with those chemicals listed in the original Bechtel Control Room Habitability Study.
[5]  Each of the chemicals included in the analysis was evaluated based on toxic, physical, and chemical properties. Some were eliminated based on Regulatory Guide 1.78 (Table C-2) criteria. The remaining chemicals were analyzed assuming a fresh air intake of 2000 ft 3/min to the air handling system and no isolation. At this flowrate, without isolation, the following chemicals exceeded the toxicity limit or TLV in the control
 
room:  acrylonitrile, ammonia, 1,3-butadiene, chlorine, ethylene oxide, and hydrochloric acid. Detailed analyses for each of these chemicals are provided in Reference 6. Protection provisions are described below.
 
6.4.4.2.3 Protection Provisions Operators are protected against the above chemicals by placing the control room HVAC system in the isolation/recirculation mode. This isolation mode provides for 100% recirculated air with no outside makeup. Operator action to isolate the control room is required (within 2 minutes after detection of odor) for chemicals whose control room concentrations would otherwise exceed the toxicity limits after that time. The chemicals requiring operator action are hydrochloric acid, chlorine, and 1,3-butadiene.
The concentration of acrylonitrile could slightly exceed the TLV in approximately 42 minutes after the plume reaches the control room air intake. This concentration is an order of magnitude below the toxicity limit and the odor threshold. The TLV has been established based on chronic effects, and for this reason air monitoring for this chemical is not necessary.
DRESDEN - UFSAR Rev. 8  June 2009    6.4-10 The estimated probabilities of control room uninhabitability due to release of ammonia or ethylene oxide are an order of magnitude below the SRP 2.2.3 criterion for realistic estimates. Therefore, the proposed risk is acceptable and monitoring is not required.
 
6.4.4.3 Fire and Smoke Protection
 
The control room HVAC system is designed to isolate and maintain the design conditions within the control room during fires in either the control room or outside the emergency zone.
Smoke detectors, located in the control room return air ducts, will annunciate in the control room and the Train A HVAC system will be switched manually to the smoke purge mode. During this mode, the system supplies 100% outdoor air. This will prevent the recirculation of smoke into any of the occupied areas in the event of fire while exhausting 100% of the return air to the outdoors. The smoke purge capability is only available on Train A. 
 
A smoke detector in the Train A control room HVAC System outside air intake will annunciate and the Train A HVAC system will be manually switched to the recirculation mode. This will prevent the intake of smoke into the control room envelope in the event of an outside fire adjacent to the  Train A HVAC system outside air intake.
 
SCBA units are located in the control room. In addition, a bank of emergency air bottles is located in the Unit 2 battery room, and can be connected to the SCBAs by 50-foot hoses stored in the control room. The control room emergency air system can be used during release of radioactivity, toxic gas, or smoke.
 
====6.4.5 Testing====
and Inspection The AFU is periodically operated and tested in accordance with Technical Specification Section 5.5.7, Ventilation filter Testing Program. 
 
====6.4.6 Instrumentation====
Requirements The AFU has instrumentation installed to support the testing outlined in Section 6.4.5. Differential pressure is monitored across the rough prefilter, the HEPA prefilter, the HEPA afterfilter, and the complete unit. Temperature is monitored at the inlet, after the electric heater, and after the activated carbon adsorber bed. An additional readout is provided as part of the electric heater temperature control circuit. The temperature element after the activated carbon adsorber provides an interlock to allow the fire protection deluge to be activated.
DRESDEN - UFSAR Rev. 4    6.4-11 6.4.7 References
: 1. Dangerous Properties of Industrial Materials, Irving Sax, Richard Lewis, Van Nostrand Reinhold, N.Y., N.Y., 1989.
: 2. Technical Guidance for Hazardous Analysis, U.S. EPA, 1987.
: 3. Handbook of Chemical Hazard Analysis Procedures, Federal Emergency Management Agency, 1989. 
: 4. Estimating Releases and Waste Treatment Efficiencies for the Toxic Chemical Release Inventory Form, U.S. EPA document 560/4-88-002, December 1987.
: 5. Control Room Habitability Study for Dresden Units 2 and 3, Commonwealth Edison Company, Bechtel Power Co., December 1981.
: 6. Control Room Habitability Study Update for Dresden Units 2 and 3, Commonwealth Edison Company, Scientech Inc., December 2000. 
 
DRESDEN - UFSAR Rev. 8               
 
June  2009  (Sheet 1of 1)
Table 6.4-1 Deleted DRESDEN - UFSAR Rev. 4    6.5-1 6.5 FISSION PRODUCT REMOVAL AND CONTROL SYSTEMS
 
====6.5.1 Engineered====
Safety Feature Filter Systems The secondary containment system is the only engineered safety feature (ESF) which uses a filter system to control fission product releases. This filter system is the standby gas treatment system (SBGTS) described in Section 6.5.3. The ESFs are described in Section 6.0.
 
====6.5.2 Containment====
Spray Systems
 
The containment spray system is part of the containment cooling system described in Section 6.2.2.
 
====6.5.3 Fission====
Product Control Systems
 
The SBGTS is provided to maintain a small negative pressure in the reactor building under isolation conditions, in order to prevent ground level escape of airborne radioactivity. Filters are provided to remove radioactive particulates, and charcoal adsorbers are provided to remove radioactive halogens which may be present in concentrations significant to environmental dose criteria. Any radioactive noble gases passing through the filter/adsorbers are diluted with air and dispersed into the atmosphere from the 310-foot chimney. The system is also used to dispose of purge and vent gases from the primary containment, and to assist with containment inerting/deinerting. The exhaust duct radiation monitor provides a continuous indication of radioactivity entering the system, and the chimney monitor samples the effluent. The SBGTS is shown in Drawing M-49. The primary containment vent, purge, and inerting systems are discussed in Section 6.2.5. The radiation monitoring system is di scussed in Section 11.5.
 
6.5.3.1 Design Objectives The system is sized to maintain the reactor building at a negative pressure of 1/4 in.H 2O relative to the atmosphere under neutral wind conditions. The nominal flowrate is 4000 ft 3/min to achieve these objectives. Two separate filter/ adsorber/ fan units are provided. One train is selected as primary and the other train is placed in standby. If the primary train fan or heater fails to start, the standby train will be started automatically. Both units receive power from the emergency electrical
 
supply. The system is designed for Class I seismic conditions. The equipment is located in the shielded center tunnel between the two main condenser rooms. The exhaust pipe runs through the radwaste building and up into the 310-foot chimney.
DRESDEN - UFSAR Rev. 8  June 2009    6.5-2 6.5.3.2 System Description In the direction of airflow, each standby gas treatment unit has the following major components:
 
A. Inlet valve - This is a motor-operated butterfly valve which is normally closed. It opens automatically upon system initiation.
 
B. Cooling air supply line - This line draws 300 ft 3/min of cooling air from the turbine building to remove decay heat from the standby SBGTS train, or can be used to purge contaminated air from the SBGTS area. Upon initiation of the primary train, a normally open motor-operated butterfly valve closes to isolate this train from the line. Cooling air is drawn via the supply line through another normally open valve into the standby train.
 
C. Demister - The demister reduces the moisture content of the steam-air mixture routed through SBGTS. It consists of a woven nylon mesh which traps water droplets. Water removed from the steam-air mixture is routed through a loop seal arrangement to the "A" waste neutralizer tank in the radwaste building.
 
D. Electric heater - The electric heater raises the temperature of the entering air by at least 14°F to ensure a relative humidity of less than 70%. The heater energizes automatically upon adequate system flow. Downstream temperature instrumentation provides an alarm in the main control room on high temperature. Station procedures direct operators to shut down the running train to ensure that the activated charcoal bed is not damaged by excessive heat. The heater is powered from the emergency bus.
E. Rough prefilter - The rough prefilter removes dust and other debris which may enter the system. This filter increases the usable life of the downstream high efficiency particulate air (HEPA) prefilter. The prefilter is capable of withstanding a temperature of 500
°F. F. HEPA prefilter - Radioactive particulates entering the SBGTS are removed by the HEPA prefilters. The HEPA filters are designed to have a removal efficiency of not less than 99% for 0.3-
µm particles and were factory-tested using PSL spheres to verify this capability. The HEPA prefilter is designed to withstand 500
°F temperatures.
G. Activated charcoal adsorber - Filtered air is passed through an activated charcoal adsorber bed capable of removing 95% of fission product iodine. Flowrates above the design range lower air retention time and lower the bed's efficiency. Samples of the carbon are placed in the adsorber inlet for periodic removal and analysis. High temperature charcoal (626
°F ignition temperature), framing, and sealing materials are specified. The bed consists of charcoal adsorbent contained in twelve cells. Each cell contains at least 50 pounds of activated charcoal for a total bed weight of at least 600 pounds. The design charcoal adsorption requirement is 95% methyl iodide removal at a relative humidity of 70% and a temperature of 30
°C (86°F). The geometry of the SBGTS charcoal cells is shown on DRESDEN - UFSAR Rev. 4    6.5-3    Figure 6.5-2. Replacement charcoal shall be qualified according to the guidelines of Regulatory Guide 1.52.
H. Test orifice - A test orifice is installed downstream of the charcoal adsorber bed. The orifice produces turbulent gas flow for more complete mixing, ensuring that the sample taken is a representative one. This orifice also serves as a flow element to automatically start the standby train on low flow in the primary train.
 
I. HEPA afterfilter - The HEPA afterfilters are similar to the HEPA prefilters (see Item F) and are provided to remove any activated charcoal particles that may be released from the activated charcoal adsorber.
 
J. Crosstie line - A crosstie line, with restricting orifice and manual butterfly valve (which is normally locked open), interconnects the two trains so that the operating train fan can provide filter decay heat cooling air at the proper flowrate through the idle train. The valve allows isolation of the two trains when required for test purposes or when one train is down for maintenance.
K. Flow control valve - This is an air-operated butterfly valve which maintains the flowrate through the train at 4000 ft 3/min +/-10% (4300 ft 3/min through the system when cooling the standby train). This valve is normally open and is controlled by the flow element in the discharge line to the 310-foot chimney.
 
L. Fan - The fans operate in parallel from a common system inlet plenum to provide flow through the two separate parallel trains. They are located downstream of the filters to minimize contamination during maintenance. Fan performance is discussed in Section 6.5.3.3. The fan performance curve is shown on Figure 6.5-3.
M. Backdraft damper - A backdraft damper is provided to ensure that reverse flow through the SBGTS filter train, which could spread contamination, will not occur. This damper acts as a check valve and closes whenever airflow into the exhaust fan occurs.
N. Outlet valve - This is a motor-operated butterfly valve which is normally closed. It opens automatically upon system initiation.
 
The SBGTS intake ducts can take suction from the reactor building ventilation system exhaust duct, the HPCI gland seal condenser exhaust, the ACAD system, the cooling air supply line, or from primary containment. The discharges from the two SBGTS trains are joined together and the discharge from the system is routed to the 310-foot chimney through a common line. Note: valves MO 2-7503 and 3-7503 are retained open with remote control removed.
SBGTS can be started manually, but is automatically initiated by a secondary containment isolation signal (as described in Section 6.2.3).
DRESDEN - UFSAR 6.5-4 6.5.3.3 Design Evaluation Figure 6.5-3 defines the head flow characteristics of the SBGTS fan. The performance of the fan under various exfiltration conditions is available from this curve. The head flow characteristic of the SBGTS fan was calculated using the polynomial method to determine the constants of the fan curve in order to equate exhaust flow as a function of the reactor building pressure. The pressure drops attributed to the components of the SBGTS are presented in Table 6.5-1. See Section 6.2.3 for an analysis of reactor building exfiltration.
 
When SBGTS is operating, the surrounding area can experience a very high dose rate. A temperature indicator and alarm is installed in the control room to monitor the temperature of the charcoal adsorber in the SBGTS and to advise the operator of limiting operating conditions. The location of this indicator also helps reduce the radiation exposure of operating personnel. The indicator setpoints (112
°C to 117°C, or 233.6
°F to 242°F), which are based on experimental and manufacturer's recommendations, are to ensure integrity of the charcoal adsorbers.
Shielded doors have been installed between the SBGTS trains and their respective control cabinets to isolate the cabinets from the harsh environment caused by the filters and adsorbers on the trains.
These doors do not adversely affect the operation of existing equipment because the shields are classified Class I and are safety related. These doors ensure equipment will operate in a suitable environment.
SBGTS fans, heaters, and dampers are supplied by 480-V ESS buses, which receive auxiliary power during a loss of offsite power (LOOP). The motor control center (MCC) for Train A of the SBGTS is fed from bus 29 in Unit 2, and the MCC for Train B is fed from bus 39 in Unit 3. There is a divisional separation between Train A and Train B cables. In this way, the SBGTS is protected against the possibility of a single failure to either the Unit 2 or Unit 3 125-Vdc battery system, concurrent with a LOCA and LOOP in the other unit, rendering both trains of the system inoperable. Section 8.3 contains a description of the emergency power system.
Bus 29 is required for post-fire safe shutdown. The load added by the SBGTS MCC must be manually disconnected from bus 29 to protect safe shutdown equipment following a fire.
 
6.5.3.4 Testing and Inspection
 
The preoperational tests of the SBGTS included a test to demonstrate that the SBGTS can maintain a negative internal pressure in the reactor building at 1/4-in.H 2O. Subsequent tests also demonstrated the effectiveness of the SBGTS to perform its designed functions as specified in the Technical Specifications. Further information on preoperational and startup testing is contained in Chapter 14.
Pressure buildup caused by plugging of filters or adsorbers, or pressure loss caused by development of leaks or channels through or around filters and adsorbers, is indicated by local instrumentation and will lead to initiation of appropriate DRESDEN - UFSAR Rev. 2    6.5-5 maintenance. Testing for clogging or leakage is performed periodically, as directed by the Technical Specifications.
 
The in-place efficiency of each HEPA filter is tested periodically with the DOP portable instrumentation. The testing must demonstrate at least 99% efficiency. Iodine removal efficiency of the charcoal adsorber is tested periodically by laboratory analysis of a test canister removed from the adsorber.
 
6.5.3.5 Instrumentation Requirements
 
The SBGTS system has instrumentation installed to support the testing outlined in Section 6.5.3.4. Differential pressure is monitored across the demister, rough prefilter, HEPA prefilter, activated charcoal bed, and HEPA afterfilter. Temperature is monitored before and after the electric heater, and before and after the activated charcoal adsorber bed. Humidity is locally indicated at the adsorber bed inlet. System flowrate is monitored at the flow control valves, at a flow element in the common discharge line and in the control room. Parameters which cause automatic initiation of the SBGTS, along with damper positions and fan operation, are monitored in the control room.
 
DRESDEN - UFSAR Rev. 01A/Dec. 1995 Table 6.5-1 PRESSURE DROPS FOR SBGTS EXHAUST TRAIN (Sheet 1 of 1)
System Components  Pressure Drop Corresponding to 4000 f 3/min (in H
{2}O)    Suction ductwork up to SBGTS 
 
===0.7 Pressure===
drop across SBGTS equipment 10.5(1) Pressure drop for flow orifice  2.0 Discharge ductwork up to base of 310-foot chimney
 
===2.0 Allowance===
for system head if ventilation air flowing in chimney
 
===0.8 Total===
16.0   
 
Notes:  1. With clean filters this Delta-P is maintained by throttling suction dampers. As filters become dirty, dampers are opened to maintain 10.5 in H{2}O. Dirty  filters have a Delta-P allowance of 4.0 in H
{2}O.   
 
DRESDEN - UFSAR Rev. 6  June 2005    6.6-1 6.6 INSERVICE INSPECTION OF CLASS 2 AND 3 COMPONENTS A summarized inservice inspection program, including information on areas subject to examination, method of examination, and relief requests, is provided in the Dresden Station Inservice Inspection
 
Plan. This section addresses inservice inspection (ISI) for ISI Class 2 and 3 components. ISI for Class 1 components is addressed in Section 5.2. Inservice inspection and testing of pumps and valves is discussed in Section 3.9.
The ISI program was developed in accordance with the requirements of 10 CFR 50.55a and the 1995 Edition with 1996 Addenda of the ASME Code Section XI. Where these rules were determined to be impractical, specific relief was requested in writing from the NRC. The NRC is authorized by 10 CFR 50.55a(g)(6)i to grant relief from the requirements of ASME Section XI upon making the necessary findings. Relief requests are included in the Dresden ISI Plan.
 
The ISI Plan is effective from January 20, 2003, through and including January 19, 2013, which represents the fourth 10-year interval of the ISI program for Dresden Station Units 2 and 3.
 
====6.6.1 Components====
Subject to Examination The construction permits for Dresden Units 2 and 3 were issued on January 10, 1966, and October 14, 1966, respectively. At that time, ASME Section III covered only pressure vessels, primarily nuclear reactor vessels, and associated piping up to and including the first isolation or check valve. Piping, pumps, and valves were built primarily to the rules of USAS B31.1, the Power Piping Standard, and so the station ISI program contains no ASME Section III Class 1, 2, or 3 designed systems. The system classifications used as a basis for the ISI program are based on the requirements given in 10 CFR 50.55a(g) and Regulatory Guide 1.26, Revision 3. These classifications were developed for the sole purpose of assigning the appropriate ISI requirements for water, steam, and radioactive waste containing components. Components within the reactor coolant pressure boundary (RCPB), as defined in 10 CFR 50.2, are designated ISI Class 1 as determined by 10 CFR 50.55 a, with the exceptions allowed by 10 CFR 50.55a(c). Other safety-related components are designated as ISI Class 2 or 3 in accordance with the guidelines of Regulatory Guide 1.26. Pursuant to 10 CFR 50.55a, Paragraph (a)(1), the ISI requirements of ASME Section XI are assigned to these components, within the constraints of existing plant design. The extent of the Class 1, 2, and 3 designations for systems or portions of systems subject to the ISI requirements are identified on the P&IDs.
 
====6.6.2 Accessibility====
Paragraphs (g)(1) and (g)(4) of 10 CFR 50.55a state that plants whose construction permits were issued prior to January 1, 1971, must meet the requirements of ASME Section XI to the extent practical within the limitations of design, DRESDEN - UFSAR Rev. 6  June 2005    6.6-2 component geometry, and material of construction of the components. Dresden's construction permit was issued prior to this date, and the as-built configuration of  ISI Class 2 and Class 3 system components sometimes does not provide adequate clearance to conduct the required inspections. In these cases, specific relief requests are made as described previously.
 
====6.6.3 Examination====
Techniques and Procedures
 
ASME Section XI, Tables IWC-2500-1, IWD-2500-1, and IWF-2500-1 specify the type of examination to be performed (visual, surface, or volumetric) within each examination category. Requirements for these examinations are given in ASME Section XI, Subarticle IWA-2200.
 
====6.6.4 Inspection====
Intervals As defined in ASME Section XI, Paragraph IWA-2432, the inspection interval is 10 years. The interval may be extended or decreased by as much as 1 year. However, such adjustments shall not cause successive intervals to be altered by more than 1 year from the original pattern of years.
The inspection frequencies for ISI Class 2 system components is that specified in ASME Section XI, Subarticle IWC-2400 and Table IWC-2500-1. The inspection freque ncies for ISI Class 3 system components is specified in ASME Section XI, Subarticle IWD-2400 and Table IWD-2500-1. The inspection frequencies for ISI Class 2 and Class 3 system component supports is specified in ASME Section XI, Subarticle IWF-2400.
 
====6.6.5 Examination====
Categories and Requirements The Dresden ISI program is organized according to the inspection categories defined in ASME Section XI, Tables IWC-2500-1 for ISI Class 2, IWD-2500-1 for ISI Class 3, and IWF-2500-1 for ISI Class 2 and Class 3 component supports.
 
====6.6.6 Evaluation====
of Examination Results Flaws detected in ISI Class 2 component examinations are evaluated according to the requirements of ASME Section XI, Articles IWA-3000 and IWC-3000. Flaws detected in ISI Class 3 component examinations are evaluated according to the requirements of ASME Section XI, Articles IWA-3000 and IWD-3000. Flaws detected in ISI Class 2 or Class 3 component support examinations are evaluated according to the requirements of ASME Section XI, Articles IWA-3000 and IWF-3000. Repair/replacement activities for ISI Class 2 and Class 3 components and component supports are performed in compliance with ASME Section XI, Article IWA-4000.
DRESDEN - UFSAR Rev. 6  June 2005    6.6-3  6.6.7 System Pressure Tests Class 2 systems are pressure tested in accordance with ASME Section XI, Article IWA-5000 and Article IWC-5000. Class 3 systems are pressure tested according to ASME Section XI, Article IWA-5000 and Article IWD-5000.
 
Dresden UFSAR Revision 2 June 1997
 
Figures 6.3-77 and 6.3-78 Deleted
 
Rev. 8 June 2009    Figure 6.4-1 DRESDEN CONTROL ROOM HVAC SCHEMATIC DRESDEN STATION UNITS 2 & 3                    DUCTWORK LOCATED OUTSIDE EMERGENCY ZONE                                  AND UNDER NEGATIVE PRESSURE SMOKE DETECTOR
 
EMERGENCY ZONE BOUNDARY Air Filter Unit EXHAUST OUTSIDE AIR (2000 CFM MAX) TRAIN A RETURN AIR FAN TRAIN A AHU ZONE 1 ZONE 2 TRAIN B AHU Booster Fans OUTSIDE AIR (2000 CFM MAX) TRAIN B EQUIPMENT ROOMUNIT 1, 2, & 3 MAIN CONTROL ROOM LEGEND LOCKER ROOM EXHAUST KITCHEN EXHAUST}}

Latest revision as of 05:20, 13 January 2025

Updated Final Safety Analysis Report (Ufsar), Revision 9, Chapter 6.0, Engineered Safety Features
ML11202A182
Person / Time
Site: Dresden  Constellation icon.png
Issue date: 06/29/2011
From:
Exelon Generation Co, Exelon Nuclear
To:
NRC/FSME
References
RS-11-100
Download: ML11202A182 (462)
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