ML20136A975
| ML20136A975 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 03/06/1997 |
| From: | Cruse C BALTIMORE GAS & ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9703100097 | |
| Download: ML20136A975 (13) | |
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CHARLES II. CRUSE Baltimore Gas and Electric Company Vice President Calven Cliffs Nuclear Power Plant Nuclear Energy 1650 Calvert Cliffs Parkway Lusby. Maryland 20657 410 495-4455 March 6,1997 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION:
Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit No. 2; Docket No. 50-318 License Amendment Request: Modification to the Service Water Head Tanks
REFERENCES:
(a)
Letter from Mr. B. K. Gri:ues (NRC) to Mr. C. H. Cruse (BGE), dated September 30, 1996, NRC Generic Letter 96-06:
" Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions" (b)
Letter from Mr. C. H. Cruse (BGE) to NRC Document Control Desk, dated January 28,1997,120-Day Response to Generic Letter 96-06,
" Assurance of Equipment Operability and Containment Integrity During Design-Basis Accident Conditions" Pursuant to 10 CFR 50.90, Baltimore Gas and Electric Company hereby requests an amendment to Operating License No. DPR-69 to allow a modification to the Unit 2 Service Water (SRW) System which constitutes an unreviewed safety question as described in 10 CFR 50.59. We propose to add a nitrogen system to the SRW head tanks to increase the pressure in the SRW System by approximately 15 psi. This proposed modification is in response to the water hamrrer concerns expressed in Generic Letter 96-06 (Reference a). The concern of the generic letter was that a loss of offsite power would disable the SRW pumps and stop flow in the SRW System for a short time. If this situation should occur concurrent with a Loss-of-Coolant Accident or Main Steam Line Break, the water in the containment air coolers (CACs) could boil as a result of the energy released to containment by the accident. The boiling would form steam voids in the CACs. The voids would collapse when SRW flow was re-established and the collapse, combined with the returning flow, would cause a water hammer, challenging the CAC(s) and/or the related SRW piping. As discussed in Reference (b), the CACs and associated equipment were shown to be operable under these conditions. After considering several options, it was determined that c. the best method for resolving this concern is to increase the pressure in the SRW System above the fluid 9703100097 970306 PDR ADOCK 05000318 P
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Document Control Desk March 6,1997 Page 2 a
saturation point, thus providing a means to prevent boiling in the CACs until the SRW pumps 7
automatically restart.
UNREVIEWED SAFETY OUESTION I
We have concluded that the addition of a nitrogen pressurization system to the SRW head tanks introduces the possibility of a failure that could affect both trains of the SRW System. The possibility of either a loss of pressurization or an overpressurization caused by the nitrogen system is a malfunction of a different type than previously evaluated in the Updated Final Safety Analysis Report. Although such failures are possible, the proposed modification is designed so that it effectively prevents negative impact i
J-on the operation of the SRW System or the CACs. Additional information concerning this determination is contained in Attachment (1). Upon approval of this request and completion of the modification, the Updated Final Safety Analysis Report will be revised to reflect the new configuration.
SCHEDULE l
We are planning to install this proposed modification in the Unit 2 outage which starts March 14,1997.
l Construction is currently planned to start March 10, 1997, and be completed by April 10, 1997.
Therefore, we ask for approval not later than April 10,1997. Both SRW subsystems and the CACs must
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be operable prior to the unit entering a Mode 4 condition, which is currently scheduled for April 30, j
1997. We consider this issue to be important and have acted as quickly as possible after the issuance of the generic letter to prepare the proposed modification for work during this outage. We will submit a j
similar request for Unit I after we have performed a design analysis specific to thst unit.
j ASSESSMENT AND REVIEW We have evaluated the significant hazards considerations associated with this proposed modification, as j
required by 10 CFR 50.92, and have determined that there are none (see Attachment 2 for a complete discussion). We have also determined that operation with the proposed modification will not result in any significant change in the types or significant increases in the amounts of any effluents that may be released offsite, and no significant increases in individual or cumulative occupational radiation exposure.
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Therefore, the proposed amendment is eligible for categorical exclusion as set forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact statement or environmental assessment is needed in connection with the approval of the proposed modification. The Plant Operations and Safety Review Committee and the Offsite Safety Review Committee have reviewed this l
proposed modification and concur that it involves no significant hazards considerations, and that operation with the proposed modification will not result in an undue risk to the health and safety of the j
public.
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Document Control Desk March 6,1997
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Should you have questions regarding this matter, we will be pleased to discuss them with you.
1 Very truly yours,
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STATE OF MARYLAND
- TO WIT:
COUNTY OF CALVERT I, Charles H. Cruse, being duly swarn, stat, that I am Vice President, Nuclear Energy Division, Baltimore Gas and Electric Compa.sy (BGE), and that I am duly authorized to execute and file this License Amendment Request on br.nalf of BGE. To the best of my knowledge and belief, the statements contair
's document are tue and correct. To the extent that these statements are not based on my J
personai.
edge, they are based upon infonnation provided by other BGE employees and/or consultartt. Such information has been reviewed in accordance with company pr ice and I believe it to be reliable.
j All AmV
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Sub rib d and sworn before a NotaryRublic in and for me State of Maryland and County of
,this b day of /RdMJV.1997.
WITNESS. my Hand and Notarial Seal:
h Notary Public kd>x.4thj / /998 My Commission Expires:
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Ddfe CHC/EMT/ dim Attachments: (1)
TechnicalInformation (2)
Determination of Significant Hazards i
(3)
Sketch of Proposed Modification ec:
D. A. Brune, Esquire H. J. Miller, NRC J. E. Silberg, Esquire Resident Inspector, NRC Director, Project Directorate I-1, NRC R.1. McLean, DNR A. W. Dromerick, NRC J. H. Walter, PSC l
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l ATTACHMENT (1) i i
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TECHNICAL INFORMATION I
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1 Calvert Cliffs Nuclear Power Plant Unit 2 March 6,1997
1 ATTACHMENT _(D TECHNICAL INFORMATION BACKGROUND Generic Letter 96-06 identified a water hammer concern in the Service Water (SRW) System. A loss of offsite power (LOOP) would disable the SRW pumps and stop flow in the SRW System until they a repowered by the emergency diesel generator (EDG). The duration of this event will be short; but, if this situation should occur concurrent with a Loss-of-Coolant Accident (LOCA) or a Main Ste (MSLB), the water in the containment air coolers (CACs) could boil as a result of the energy relea:,ed the accident.
The steam would collapse when SRW flow was re-established which would result in a water hammer. Water hammer loads were not included in the original design basis for the SRW System.
One way to prevent boiling for the time required to restart SRW flow is to raise the pressure in the system. Analysis has shown that a 14 psi pressure increase will delay the onset of boiling by approximately 30 seconds. This is sufficient time for the SRW pumps to restart and re-establish flow and make boiling no longer credible. Therefore, a modification to the system is being proposed which will increase the SRW System pressure by approximately 15 psi, thus providing a means to prevent boiling in the CACs until the SRW pumps automatically restart. This proposed modification ensures a margin of approximately 4 seconds between pump start and the potential onset of boiling. The proposed l
modification to the SRW System will increase the system operating pressure by utilizing a nitrogen blanket in the SRW head tanks. The higher pressure will prevent boiling in the CACs by maintaining SRW pressure above the fluid saturation pressure.
l DESCRIPTION OF EXISTING CONFIGURATION The SRW System is a closed cooling water system designed to remove heat from various safety-related and non-safety-related plant components. The SRW System functions as one system for non-safety-related heat loads in the Turbine Building, and is divided into two subsystems by manually operated valves for the safety-related heat loads in the Auxiliary Building and Containment. Subsystem 21 supplies flow through the SRW heat exchangers to the Nos. 21 and 22 CACs. Subsystem 22 supplies flow through the SRW heat exchangers to the Nos. 23 and 24 CACs. However, any CAC can be supplied from either subsystem by positioning local manually-operated valves. A head tank in each subsystem provides net positive suction head and surge protection for the system. Each head tank has a 4
normally-open vent valve to the Auxiliary Building atmosphere, which can be isolated with a manual isolation valve. Currently, six-inch overflow lines connect the gas space of the Nos. 21 and 22 head tanks.
Containment Air Coolen Four, two-speed CACs are provided to remove ambient heat from containment during normal plant operation. Service water is the cooling agent. In the event of a LOCA or MSLB, the CACs contribute to limiting the containment pressure rise to below the design value.
Service Water Head Tanks The two 2350 gallon SRW head tanks provide surge capacity to accommodate system volume changes.
Each tank supplies its respective subsystem. The head tank level is automatically maintained. A level switch signals the level control valve to open and close to add water to the tank. Head tank level may also be controlled by a manual bypass valve. Normally, make-up water to the head tanks can be supplied from either the Demineralized Water System or Condensate System. Emergency make-up can be l
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ATTACHMENT (1)
TECHNICAL INFORMATION provided by Fire Protection and Saltwater Systems. These systems have Feen evaluated for the increased pressure in the head tanks.
Head tank level indication is provided by local sight-glass level indication and remote level indication.
The remote indication ls in the Main Control Room and alarms on increasing high level, and decreasing low level.
Each head tank has a manual vent valve located on top of the tank. A combined overflow line for the head tanks provides surge capacity between tanks and serves as overflow protection. The overflow line is directed to an Auxiliary Building floor drain located on the 69-foot elevation. The current head tank maximum allowed working pressure and temperature are 15 psig and 150 F.
l DESCRIPTION OF PROPOSED MODIFICAIlOE This proposed modification uses pressurized nitrogen gas as a source for providing the required cover gas pressure ir N SRW head tanks. The plant nitrogen system will be used to pressurize two safety-related nitrogen accumulators (one for each head tank) required for this proposed modification. Piping i
connections will be provided to allow the temporary use of nitrogen bottles to pressurize the accumulator tanks to provide an alternate nitrogen supply. Nitrogen to the head tanks will be reduced to approximately 15 psi by pressure regulators, which will raise the operating pressure of the SRW System by approximately 15 psi. A sketch of the proposed modification is provided in Attachment (3).
Because the proposed modification increases the normal operating pressure of the SRW System by 15 psi, design changes will be incorporated, as required, to ensure that the design pressure of each SRW component is at or above the new local maximum operating pressure. All components of the SRW System and the new nitrogen system are being reviewed for compliance to the appropriate design code.
Additionally, the increase in the SRW operating pressure has no adverse impact on the operation of the SRW pumps. The addition of a 15 psi nitrogen blanket in the SRW head tanks will have no adverse impact on water chemistry, since the absorption of nitrogen gas in water is minimal.
The SRW isolation valves listed in UFSAR Table 9-17A remain capable of closing assuming the new operating pressures, and this proposed modification has no significant impact on their closing times.
Additionally, this proposed modification will not impact the capability of the SRW check valves listed in the same table to close under reverse pressure conditions.
Gaseous relief protection is being provided for both the accumulators and the nitrogen supply header.
The discharge from the gaseous relief valves will be routed to an existing plant ventilation duct upstream of the radiatior mnitor. The discharge is not anticipated to contain radioactive material, but will be routed to the i m ystem for personnel protection should the relief valve lift.
This proposec. w fication also adds water relief valves to the head tanks. The relief valves will be mounted on the cross-connect line. The relief valve discharge will be routed to the same floor drain as the existing overflow line. Since the nitrogen supply will be designed to accommodate anticipated head tank level fluctuations, it is expected that the water relief valve would rarely lift, thus having negligible impact on the floor drain system.
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ATTACHMENT (1) l i
TECHNICAL INFORMATION UNREVIEWED SAFETY OUESTION We have concluded that, when installed, the proposed modification will constitute an unreviewed safety question because it introduces a new possibility of a malfunction of equipment important to safety that was not previously discussed in the Updated Final Safety Analysis Report for Calvert Cliffs. The proposed modification adds pressurized nitrogen to raise pressure in the SRW head tanks by approximately 15 psi. The head tanks are currently vented.
SAFETY ANALYSIS l
To determine if there is an effect on plant safety resulting from this proposed modification, an evaluation was done of the various malfunctions that could occur if the nitrogen system was added to both head tanks.
l Service Water System The proposed modification provides two redundant nitrogen accumulators, and each accumulatcr has the capacity to maintain approximately 15 psig nitrogen pressure in both the head tanks. The nitrogen accumulators and the associated relief valves, pressure regulators, and piping are safety-related, Seismic Category 1. Control Room annunciation is provided for the nitrogen pressure.
l A possible malfunction of the pressure regulator was evaluated. The regulator can either fail open or closed. The equipment important to safety, previously evaluated, affected by these malfunctions are both SRW subsystems. The effect of each of these malfunctions is described below. The conclusion of the evaluation is that the installation of this proposed modification does not negatively impact the operation of the SRW System.
If either pressure regulator were to fail open, it could potentially overpressurize the SRW System. To prevent the overpressurization, a full-flow relief valve and a check valve are designed to be installed on the head tank side of each pressure regulator (see Attachment 3). The relief valves will ralieve se excess pressure and the check valves will isolate the failed regulator from the rest of the nitrogen system.
Likewise, if a pressure regulator should fail shut, the check valve would isolate it from the remainder of the nitrogen system. In both situations, the nitrogen supply in the unatTected part of the nitrogen system is sufficient to maintain pressure on both head tanks.
The proposed nitrogen supply to the SRW System is only required during the first 30 seconds of a LOCA or MSLB concurrent with a LOOP. The SRW pumps will have started by that time and the possibility of a water hammer would have passed. A passive failure of the SRW System, including the proposed modification, is not required to be evaluated during this time in the acMent sequence. A passive failure i
in the SRW System is evaluated for the period following the recirculation from the containment. Such a passive failure would result in the loss of nitrogen pressure, however, pressurization of the SRW System is not required during this phase of the accident.
The single failure analysis in UFSAR Table 9-17A was reviewed. The table shows that no single active failure of the SRW System at any time, nor any single passive failure after recirculation from the containment would prevent the SRW System from fulfilling its safety function. This proposed modification does not alter this conclusion in any way.
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ATTACHMENT (1) l TECIINICAL INFORMATION Containment Air Coolers The CAC malfunctions which could be affected by this activity, and were previously evaluated in the Updated Final Safety Analysis Report (UFSAR Table 6-9), are cooler tube failure and failure of the SRW emergency outlet control valve fail to open.
Since the design pressure of the CAC is above the new maximum SRW operating pressure, this proposed modification will not increase the probability of the CAC tube failure. Neither will the proposed modification increase the differential pressure across the SRW emergency outlet control valve. The proposed modification will maintain the reliability of the CACs by preventing the undesired water hamtr.er loadings which could damage the CACs during a LOCA.
CONCLUSION The proposed modification has been determined to constitute an unreviewed safety question as defined in 10 CFR 50.59. We are adding nitrogen system components to the SRW System. This change may create a small increase in the probability the SRW System will be vulnerable to malfunctions of equipment not previously evaluated in the Calvert Clif1b Updated Final Safety Analysis Report. The safety significance of this proposed modification, as explained above, is minimal as redundant equipment is available to respond to any accident conditions and any failure mechanism of the components added to the SRW i
System. Therefore, per 10 CFR 50.59(2)(c), we request the NRC review and approve this proposed modification through an amendment to our Unit 2 operating license.
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DETERMINATION OF SIGNIFICANT HAZARDS i
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i Calvert Cliffs Nuclear Power Plant Unit 2 i
March 6,1997 l
ATTACHMENT m DETERMINATION OF SIGNIFICANT HAZARDS I
The proposed modification is the result of an analysis of the Service Water (SRW) System in response to Generic Letter 96-06, which identified a water hammer concern where the SRW System interfaces with the containment air coolers. The proposed modification adds a nitrogen blanket to the SRW System.
This nitrogen system will increase the pressure in the SRW System to prevent water hammer conditions from occurring. The nitrogen system adds numerous components to the SRW System.
j The safety function of the SRW System is to provide cooling to the containment air coolers and emergency diesel generators following a design basis accident. With this proposed m.odification in place, the SRW System will continue to meet this safety function. All of the failure mechanisms for this proposed modification have previously been evaluated and were found acceptable. However, because the proposed modification introduces a malfunction of a different type than any previously evaluated in the Updated Final Safety Analysis Report, this proposed modification has been determined to be an unreviewed safety question.
The proposed change has been evaluated against the standards in 10 CFR 50.92 and has been determined f
to not involve a significant hazards consideration, in that operation of the facility in accordance with the proposed amendments:
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Would not involve a significant increase in the probability or consequences of an accident previously evaluated.
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Neither the SRW System nor any SRW component is an initiator to an accident. The SRW System provides cooling to safety-related equipment following an accident. It supports accident mitigation functions. Therefore, this proposed modification does not significantly increase the probability of an accident previously evaluated.
The SRW System provides cooling water to the containment air coolers to mitigate the consequences of a loss-of-coolant accident or main steam line break. A loss of nitrogen pressure to the SRW System due to a single active failure has been evaluated. Since the nitrogen pressurization system is redundant, a single active failure in the nitrogen system would not prevent the SRW System from performing its safety function. Therefore this proposed modification does not involve a significant increase in the consequences of an accident.
Therefore, this proposed modification does not involve a significant increase in the probability or consequences of an accident previously evaluated.
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Would not create the possibility of a new or diferent type of accident from any accident previously evaluated.
The SRW System provides cooling water to the containment air coolers and emergency diesel generators. The purpose of the components which are affected by this proposed modification is to mitigate accidents. This proposed modification does not change equipment function, or significantly alter the method of operating equipment to be modified. The system will continue to operate in essentially the same manner as before the proposed modification was done.
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AIIACHMENT (2)
DETERMINATION OF SIGNIFICANT HAZARDS Therefore, the proposed change does not create the possibility of a new or different type of accident from any accident previously evaluated.
3.
Would not involve a significant reduction in a margin ofsafety.
The margin of safety in this case is the degree to which a single failure of the nitrogen system can affect the SRW System, since it connects to both SRW head tanks. To determine if there would be an adverse effect on plant safety resulting from this proposed modification, an evaluation of malfunctions of the nitrogen pressurization system was conducted. The only credible malfunctions are those related to failure of the pressure regulator. Even if a regulator were to fail open or closed, the SRW System can perform its safety function. The proposed modification includes design features which ensure that pressure is maintained in each subsystem, even if this single failure occurs. Therefore, this proposed modification maintains the ability of the SRW System to properly respond to an accident.
Therefore, this proposed modification does not significantly reduce the margin of safety.
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ATTACHMENT (3) 4
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