ML20138B002
| ML20138B002 | |
| Person / Time | |
|---|---|
| Site: | Hope Creek  |
| Issue date: | 03/17/1986 |
| From: | Corbin McNeil Public Service Enterprise Group |
| To: | Adensam E Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8603200249 | |
| Download: ML20138B002 (22) | |
Text
,D Public Service Electric and Gas Company q.g Cerbin A. McNeill, Jr.
Pubhc Service Electnc and Gas Company P.O. Box 236, Hancocks Bridge, NJ 08038 609 339-4800 Vice President -
Nuclear March 17, 1986 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission 7920 Norfolk Avenue Bethesda, Maryland 20814 Attention:
Ms.'Elinor Adensam, Dibactor Project Directorate 3 Division of BWR Licensing
Dear Ms. Adensam:
MAIN STEAM ISOLATION VALVE SEALING SYSTEM HOPE CREEK GENERATING STATION DOCKET NO. 50-354 As a result of discussions with various members of the Nuclear Regulatory Commission (NRC) staff, Public Service Electric and Gas Company (PSE&G) has reviewed the initiation and operation of the Main Steam Isolation Valve Sealing System (MSIVSS) and herein presents those arguments necessary to support 10CFR50 Appendix J Exemption Request #4 (letter from C.A.
McNeill to E.
Adensam dated December 12, 1985).
The information discussed in this transmittal serves to clarify the design bases of the MSIVSS, address the permissives necessary for system operation and justify the testing required to demonstrate system integrity.
For those design basis accidents (DBAs) which result in radioactive releases (i.e. indicative of fuel damage or cladding failure), Emergency Operating Procedure (EOP)
OP-EO.ZZ-104(Q), Radioactive Releases, will be initiated when such releases exceed ten times those specified in 10CFR20 (i.e. the alert level of the Emergency Classification Guideline [ECG]).
This EOP requires the initiation of the MSIVSS, through the implementation of Station Operating Procedure OP-SO.KP-001(Q), once the RPV has been depressurized (see Attachment 1).
The reliance upon the referenced EOP assures initiation of the MSIVSS under any possible scenario resulting in an offsite radioactive release, including accident scenarios outside the bounds of a DBA which may not result in RPV depressurization within the 20 minute time frame for the DBA-LOCA.
Hence, for the worst case
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Director of Nuclear 2
3-17-86 Reactor Regulation DBA, a large break LOCA, RPV depressurization will occur and the MSIVSS will be initiated (as radioactive releases are expected) within approximately 20 minutes such that offsite doses are maintained within 10CFR100 limits.
The MSIVSS permissive setpoint has been revised from 20 psig to 25 psig to~ assure the system maintains a 5 psi positive pressure differential between the isolated portions of the main steam lines (between the inboard and outboard MSIVs and between the outboard MSIVs and main steam stop valves [MSSVs]) and the RPV, since the drywell pressure can rise as high as approximately 17.5 psig after depressurization from a large break, design-basis LOCA (Figure.6.2-7).
The 25 psig setpoint has no impact on MSIV leakage (if the correction factor discussed below is utilized) nor the results of the analyses presented in the February 27, 1986 letter from PSE&G (C.A. McNeill) to the NRC (E. Adensam)
(with the exception of the actual references to it) and in fact would create a stronger argument for conducting a 5 psi differential LLRT when compared to a 25 psi differential LLRT if the Final Draft of the Technical Specifications had specified such a test.
Recent discussions with the NRC have revealed the need for a mathematical correction to the as-conducted 5 psig LLRT of the MSIVs to account for density effects which would be apparent if the 5 psid test had been performed at system initiation pressure (25 psig).
The correction factor obtained in Attachment 2 was determined by assuming that the entire pressure differential of 5 psi occurs across a single, square-edged orifice using Equation 3-22 from j
Crane Technical Paper No. 410, Twenty-second Printing -
1985.
Since the MSIVSS controls the differential pressure at 5 psi above the RPV pressure, the unseating force seen by the valve is the same for a 5 psig test pressure as for a 25 psig test pressure. -Therefore, it is reasonable to assume that the geometry of the leak path is comparable for both cases and thus when a ratio of the mass flow rates i
for both cases is made, the geometry terms divide out and i
do not affect the final correction factor.
The only remaining terms are tne net expansion factor (Y) and the densities.
The use of a net expansion factor for a nozzle or venturi meter is clearly inappropriate since these devices have smooth, gradual dimension changes which are quite unlike the case under consideration.
In reality, the flow path consists of numerous contractions, expansions and changes in direction through microscopic openings between the valve l
disk and body seating surfaces.
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Director of Nuclear 3
3-17-86 Reactor Regulation Therefore, the square-edged orifice model was chosen and is a conservative model of the actual leakage past the MSIV seat, and Crane Equation 3-22 was utilized in determining the correction factor obtained in Attachment 2.
The results of the calculation indicate that a 48% correction factor should be utilized when multiplying the sum of the measured leakage rate (obtained from a 5 psig LLRT) through all four main steam lines, to determine the actual leakage which would have been recorded if it was practical to test the MSIVs at the maximum MSIVSS operational pressure.
Recent discussions with Dr. Roger Kamm, Associate Professor of Mechanical Engineering at the Massachusetts Institute of Technology, have confirmed the conservative nature of the modeling equation used and the correction factor employed for the MSIV LLRTs.
Hence this correction will be incorporated in Inservice Inspection (ISI) Procedure M9-ILP-303, Local Leak Rate Testing. contains revised Final Safety Analysis Report (FSAR) Sections 6.2, 6.7 and 15.6 which reflect the discussions presented above.
Should you have any questions on the subject filing, do not hesitate to contact us.
Sincerely, Attachments (2)
Enclosure (1)
C D.H. Wagner USNRC Licensing Project Manager R.W.
Borchardt USNRC Senior Resident Inspector
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ATTACHMENT 2 CALCULATION OF THE LLRT CORRECTION FACTOR UTILIZED WHEN DETERMINING THE LEAKAGE RATE THROUGH THE MAIN STEAM LINES Equation 3-22 of-Crane Technical Paper No. 410-(1985)
(24700)(Y)(d12)(C) 9h=
[](A P)(j l)]
p gg Where:
q'h
= Flow (scfh)
Y
= Net expansion factor dl
= Orifice diameter (inches)
C
= Flow coefficient S
= Specific gravity (1.0 for air) g AP
= Differential pressure (psi) y[1
= Weight density of upstream fluid (1b /ft')
m In addition, let subscript 5 refer to the 5 psig test and 25 refer to a 25 psig condition.
Then (excluding ~S which g
is 1.0 for air):
q'h (24700)(Y25)[(d12)25](C25)[]( A P25)(/1)25 l 25 (24700)(YS)[(d12)S](C5 ) [ V( 6 P5)()91)S l q'h5 Because the valve geometry is the same for both conditions:
(di)5 = (di)25 C5=C25 Similarly, because both cases are based on a 5 psi differential:
di P
= 2L P S
25 i
i i
Dividing out all common terms yields:
9'h Y25 Y()9 3 25 I
1 l
25
=
9'h YSIY(sfl} 5 l 5
25I((/1)25 l Y
9'h (9'h5}
=
25 YSIVi81)S l j
Because the density ratio is independent of temperature, a test temperature of 70 F is chosen:
(/1)5
= 0.1005 (Crane pg. A-10)
(fl)25 = 0.2025 (Crane pg. A-10) j Because the effective flow area is small relative to the pipe cross sectional area, /s*0, and therefore can be conservatively approximated asg=0.2, k=1.4(air), in order to determine Y.
Y5
= 0.925 (Crane page A-21)
Y25
= 0.965 (Crane page A-21)
Substituting:
0.965 0.2025 q'h25 (9'h '
=
5 q'h
= 1.48 (q'h 25 5
Hence, the combined leakage rate for all four main steam lines when tested at 5 psig (i.e. the LLRT of the MSIVs, qh5) will be multiplied by a correction factor of 1.48 in order to mathematically correct the leakage past the MSIVs to what would be expected if the valves were tested at 25 psig, q'h~5 (the MSIVSS maximum operational pressure).
2 This correction is necessary since it is not practical to conduct a 25 psig LLRT, with a,5 psid across the inboard MSIVs, and simply reflects the leakage rate which would be obtained if it were practical to conduct a 25 psig LLRT.
4 4
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i ENCLOSURE I
)
6.2.5.3.5 Results The analysis was undertaken to determine the capabilities of the recombiners to control oxygen concentration inside the primary containment and to determine the impact of MSIV air inleakages on recombiner operation post-LOCA.
a.
Oxygen / hydrogen concentrations - With an initial containment oxygen concentration of 4%, the recombiner would be required to start at 1.52 days post-LOCA when the oxygen concentration exceeds 4.5%.
The oxygen concentration initially decreases due to the increase of temperature and steam in the containment and then increases due to the additional air inleakage from the MSIV.
At 1.52 days, it decreases again due to the recombiner operation; but as the containment hydrogen concentration is depleted, the oxygen concentration eventually builds up again due to the continuous MSIV leakage.
At 39 days post-LOCA, the oxygen concentration exceeds 5%.
The hydrogen concentration is negligible, however, thereby maintaining the ability to prevent hydrogen burning.
In cases with a TMI-type design situation where large quantities of hydrogen are released, the hydrogen would continue to recombine with the oxygen from the MSIV air inleakage for a longer time until all the H, is recombined.
This is possible as the oxygen removal rate by the recombiner exceeds the total oxygen addition rate by radiolysis and MSIV air inleakages.
b.
Containment pressure - The recombiner is limited to operate at full flow only at pressures less than 30 psia.
For a design basis accident (DBA)-LOCA, the containment pressure is below 27 psia after 1.25 days, which is before the recombiner is required to operate due to reaching a 4.5% oxygen concentration.
The increase in pressurer'due to the MSIV air inleakage at the/r'.5 sc:.9/vcivc reaches 27 psia at 137 davs after CNRBNED the accident.
It does not reach 45.7 psia (3'1 psig) or FAEF CC half of the peak design pressure according to 96ffEH SRP 6.2.5,Section II.4, until approximately 450 days RDE QLC after the accident.
These time-periods are well beyond-1 Fbuft the point when iodine releases due to venting to ropio maintain the pressure would result in significant
$1EAM offsite doses.
Figures 6.2-39 and 6.2-40 are plots of UMGS 6.2-83
HCGS FSAR 10/84 the post-LOCA. containment pressure versus time up to 180 days af ter the accident.
The discussion above indicates that the~recombiners are adequate to control the oxygen concentration inside the primary containment post-LOCA.
The results presented are based on the following conditions:
1.
4%-initial oxygen concentration 2.
4-1/2% oxygen concentration for recombiner actuation gI J'
Foe Av Rok 3.
scfh air inleakagegner LIM pudo susont UWS CorHBwsb 4.
150 scfm maximum recombiner flow.
Figures 6.2-32 and 6.2-33 show the hydrogen and oxygen concentrations versus time in the drywell.
Figures 6.2-34 and 6.2-35 show the concentrations in the suppression pool air space.
All four figures show the concentrations for the. case using no recombiners and for the case with one train of the recombiner system operating at its design flow of 150 cfm.
Figures 6.2-36 and 6.2-37 show the cumulative total oxygen and hydrogen generated.inside the containment.
As indicated by the oxygen and hydrogen concentrations in the previous figures, the recombiner capacity of 150 scfm exceeds the hydrogen and oxygen generation rates at all times during the accident.
Both hydrogen and oxygen concentrations are monitored following a postulated LOCA.
The hydrogen recombiners will be started under either of the following conditions:
a.
Oxygen concentration is greater than 5% and hydrogen concentration reaches 3.5%, or b.
Hydrogen concentration is greater than 4% and oxygen concentration reaches 4.5%.
Table 6.2-21a provides the peak hydrogen and oxygen concentrations inside the drywell and suppression chamber immediately following recombiner actuation.
4 i
6.2-84 Amendment 8
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6.7 MAIN STEAM ISOLATION VALVE SEALING SYSTEM LEQ6M The main steam isolation valve (MSIV) sealing system limits the BASG leakage of fission products through the MSIVs following a\\ loss-ACCU 9K of-coolant accident 4LOCA).
This is accomplished by pressurizina UE399-the sections of the main steam lines between the inboard MSIVs
~
ONEAK and the outboard MSIVs, and between the outboard MSIVs and the main steam stop valves (MSSVs) to a pressure above that of the DBA-reactor pressure vessel (RPV).
Leakage through the inboard MSIVs into the primary containment continues throughout the post-accident period, but does not jeopardize primary containment integrity, as discussed in Section 6.2.5.
6.7.1 DESIGN BASES 6.7.1.1 Safety Criteria The following criteria represent system design, safety, and performance requirements imposed on the MSIV sealing system:
r' a.
The MSIV sealing system is designed with sufficient capacity and capability to limit the leakage from the main steam lines for as long as postulated accident conditions require primary containment integrity to be maintained.
b.
The MSIV sealing system conforms to Seismic Category I requirements.
The MSIV sealing system is capable of performing its c.
safety function considering. effects resulting from a l Dl3A-l LOCA, including missiles that may result from equipment failures, dynamic effects associated with pipe whip and 1
jet forces, and normal operating and accident-caused local environmental conditions consistent with the design basis accident (DBA).
d.
The MSIV sealing system is capable of performing its g,ggggg safety'functionsgcllown LgEA and an assumed single s'n A DBA-00G active failure, including failure of any one of the MSIVs to close.
- =.
6.7-1
(
e.
The MSIV sealing system is designed so that the integrity or operability of the main steam lines or the MSIVs is not affected by a single active component failure.
f.
The MSIV sealing system is capable of performing its safety function following a loss of offcite power (LOP) coincident with afLOCA.
g.
The MSIV sealing system is remota-manually actuated and ggggi designed to permit actuation with!.nf20 minutes after a
,jrLOCA.
This time period is consistant with loading IDBA-l requirements of the Class 1E electrical buses and reasonable times for operator action.
h.
The MSIV sealing system controls include interlocks to prevent inadvertent operation of the MSIV sealing system.
In particular, interlocks are provided to prevent multiple valve openings that would result in blowing high pressure steam to the building volume whenever the pressure in the connecting main steam lines exceeds the MSIV sealing system initiating i
pressure.
1.
The MSIV sealing system, including instrumentation and circuits necessary for the functioning of the system, is designed in accordance with standards applicable to an engineered safety feature (ESF) system.
.j.
The MSIV sealing system is designed to permit testing of the operability of controls and actuating devices during power operation to the extent practical, and to permit testing of the complete functioning of the system during plant shutdowns.
k.
The MSIV sealing system is designed so that any effects resulting from the use of air or nitrogen as a sealing medium will not affect the structural integrity or operability of the main steam lines or MSIVs.
r 6.7-2
6.7.1.2 Regulatory Acceptance The piping and components of the inboard MSIV sealing system from the main steam line drain line connection, to and including the inboard MSIV sealing system isolation valve. are Quality Group A, as supplemented by Appendix A of Regulatory Guide 1.96.
The rest of the piping and components are Quality Group B, with the exception of the test line from valves HV-6055A and HV-6055B to valve HV-6057, which is Quality Group D.
The piping and components of the outboard MSIV sealing system are classified as Quality Group B.
The portion of the primary containment instrument gas system, which supplies sealing gas to the MSIV sealing system, is a Quality Group B.
All applicable codes and addenda used in the design.of the MSIV sealing system are discussed in Section 3.2.
The overall system conforms to Regulatory Guide 1.96, as discussed in Section 1.8.
b 6.7.1.3 Leakace Rate Requirements The design features employed with this system are established to reduce the dose rate of radioactive materials released to the environment following a$LOCA.
I DDA ~i imposed on the MSIV sealing system to: Leakage control requirements are I
Eliminate the potential for MSIV leakage that would a.
otherwise bypass filtration, recirculation, and ventilation (FRVS) system filtration b.
Handle technical specification leakage rates c.
Provide features to allow leakage rate verification test at every refueling shutdown d.
Allow limited component operability tests during normal operation.
6.7-3 n
The design and operational requirements imposed on the MSIV sealing. system relative to the foregoing criteria are established to:
>Y' gg ecpp a.
Allow?MSIV leakage rates of up tom 11.5 ccfh for cacM Schccrd "5!V in cach; main steam lines gg Fbt FU.
]
FouR.
b.
Ensure and limit total plant radiation dose impacts below 10 CFR 100 guidelines.
6.7.2 SYSTEM DESCRIPTION The main steam isolation valve (MSIV) sealing system is designed to eliminate the release of fission products through the MSIVs that would bypass filtration, recirculation, and ventilation system (FRVS) filtration after afLOCA.
This is accomplished by
[DBA
,1 pressurizing the sections of the main steam lines between.the inboard and the outboard MSIVs, and between the outboard MSIVs and the main steam stop valves (MSSVs),-to a pressure above that of the reactor pressure vessel (RPV).
Sealing gas is supplied from two independent primary containment instrument gas receivers.
The primary containment instrument gas system components are located in the reactor building and consist of two 100%-capacity compressor trains.
The MSIV sealing system piping and instrument diagram (P&ID) is shown on Figure 6.7-1.
The primary containment instrument gas system P&ID is shown on Figure 9.3-11.
As indicated on Figures 6.7-1 and 9.3-11, two independent subsystems (inboard and outboard) are provided to accomplish the leakage control function.
The inboard subsystem receives power from Class 1E electrical channel D and the outboard subsystem gets its power from Class 1E electrical. channel C.
6.7.2.1 Inboard Subsystem The inboard MSIV sealing system injects gas into the main steam lines between the inboard and the outboard MSIVs.
Upon initiation, gas from the gas receiver of the primary containment instrument gas system passes throughua pressure differential control valve that maintains system pressure 5 psi above the reactor vessel pressure, ja flow element,l a motor-6.7-4
/
operated isolation valve, and then a piping system that divides into four lines, one for each main steam line.
The gas then passes through a check valve, motor-operated isolation valve, and finally into the main steam line.
Pressure sensors, sensing seal gas lin'e, and reactor vessel pressures are used in regulating the pressure differential between the reactor vessel and the seal gas system at 5 psi.
In case of gross leakage through the inboard MSIV, a timer is used for reclosing the pressure differential control valve.
A flow indicator in the main control room is used to monitor the flow through the flow element.
Pressure sensors are also provided for monitoring the main steam line pressure between the inboard and the outboard MSIVs.
The pressure is monitored in the main control room.
High or low Ib"?VE! pressure in (he main steam line causes an alarm in the main control room. / m Icc.Mc?are provided such that the motor-operated isolation valves connected to each main steam line can not be opened when the main steam line pressurefis above g psig.
TIE IW-8%2D #b Check valves installed in the air supply lines provide backups for the interlocks.
g H9Vs 6.7.2.2 Outboard Subsystem The outboard MSIV sealing system connects to the main steam lines between the outboard MSIVs and the MSSVs.
The outboard subsystem is similar to that of the inboard MSIV sealing system except for instrumentation.
The differences are the two pressure transmitters that monitor the pressure between the outboard MSIVs and the MSSVs.
These pressure transmitters are used by the isolation valves of the four branches of the outboard MSIV sealing system for their common interlocks since they are located in the main steam line drain header, which is common to the four main steam lines.
6.7.2.3-System Operation During normal plant operation, the MSIV sealing system is in a standby mode with the gas receivers of the primary containment 6.7-5 Amendment 10
HCGS FSAR 5/85 E6P4BJ 8AMD instrument. gas system charged to a pressure of4105 psig, so that gas supply is available upon demand.
' DBA-izrAj
'IM%X*24Within\\20 minutes af ter a kccc-Of-ccclant accident 'LOCA), cc
,3 beiderced by nige dry'zell pressure and/or Icu reacter unter icvcl / the system EE# manually initiated from the main control Wawr1 roomdafter the op,erator verifies that the MSIVs and the SSVs are 'wgt gg; A
I shut'and the main steam line pressure has dropped to (psig or OE0
~
less.
Upon initiation, and if all 2-"eric^erSare satisfied, the
,q,gggg3j motor-operated isolation valves can?be opened, allowing gas from the primary containment instrument gas receivers to enter the main steam lines.
The MSIV sealing system is designed based on ahiminimur precrure ir the maar stear line et e psig at the time of cycter initiation to a maximum precrure of 20 prig.
This prevents the lifting of the MSIV dicP The MSI" car be unseated by a back preccure dif f erentia! ef 25 Ori; A flow element measures the gas flow through each subsystem and provides a signal to a flow switch and a timer.
Whenever the flow exceeds the setpoint of the flow switch, the timer is started.
The timer will run for a specified amount of time unless the flow drops.below the flow setpoint.
If the timer should run out it will close the pressure differential control valve.
Thus, gross leakage from the system is prevented because of this automatic action of the timer.
Each individual steam line is capable of being isolated.
Either the inboard or the outboard subsystem is capable of performing the leakage control function.
Pressures in the system and in the RPV, as well as the gas flow, are monitored in the main control r_oom.
The inboard and the outboard MSIV sealing system are remote-manually initiated separately.from the control room.
The outboard subsystem is initiated after the inboard MSIV sealing system has been started.
/ ^
s 6.7-6 Amendment 10
k 1
INSERT A FOR PAGE 6.7-6 (1) if offsite~ releases exceed 10 times those allowed by 10CFR20 (i.e. the Alert level of the ECGS), and (2) if the RPV is depres-surized (i.e. below 20 psig), and'only i
-INSERT B FOR PAGE 6.7-6
-DBA LOCA for breaks 2 ft* and larger in which RPV depressurization will occur in less than 20 minutes.
Hence the maximum containment pressure following this LOCA will.be approximately 17.5 psig (Figure 6.2-7) while the minimum pressure can be 0 psig.
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6.7.2.4 Eauiprient Reauired The following equipment / components are provided:
a.
Piping - Process piping is carbon steel pipe throughout and it is designed and constructed to ASME B&PV Code, as discussed in Section 3.2.
b.
Valves - Motor-operated, air-operated, relief, and check valves c.
Instrumentation - The requirements and criteria for the MSIV sealing system instrumentation are discussed in Chapter 7.
The remainder of the piping and components are discussed in Section 9.3.6.
6.7.3 SYSTEM EVALUATION An evaluation of the capability of the main steam isolation valve DBA -
(MSIV) sealing system to control the release of radioactivity LeCA from the MSIVs following ainccc ci-ccclent eccident ' Lec?. : has been conducted.
The resultsfof this evaluation are presented in the following sections.
6.7.3.1 Functional Protection Features The equipment in the two independent subsystems (inboard and outboard) are physically separated.
The equipment is designed to operate under the expected environmental conditions appropriate to the equipment location.
The MSIV sealing system equipment is protected by separation and barrier from exposure of the system components to internal missiles caused by eauipment failure (see Section 3.5.1), pipe I UDA,
breaks, and jet forces caused by the\\LOCA event.
Equipment is located in the reactor building, hence the effects of the design basis recirculation line break and postulated external missiles l
would not impact the system ability to function.
Furthermore, the primary containment instrument gas system equipment that supplies gas to the MSIV sealing system is located in the reactor
~
(
building outside the steam tunnel.
6.7-7 Amendment 7
HCGS FSAR The use of Class 1E power sources to power the components of the system ensures system operation during loss of offsite power (LOP).
6.7.3.2 Effects of Single Active Failures The MSIV sealing system functions following an active component failure (including any one MSIV failure to close) by virtue of two redundant subsystems.
The subsystems are independently powered from two separate divisions of the Class 1E power supply.
The effects of other failure modes are evaluated in Section 6.7.3.6.
6.7.3.3 Effects of Seismic-Induced Failures The MSIV sealing system is designed to operate during and following the application of Seismic Category I design loads in conjunction with operating loads associated with LOCA.
6.7.3.4 Isolation Provisions Containment isolation is provided by automatic closure of the inboard MSIVs and inboard MSIV sealing system isolation valves.
The inboard MSIV sealing system isolation valves have interlocks to prevent their opening when the pressure in the main steam line is greater than-the design rating of the sealing system.
One out of two valves satisfies containment isolation requirements.
Isolation (separation) of electrical components is discussed in Chapter 8.
6.7.3.5 Leakaae Protection Evaluation The MSIV sealing system is designed to limit the release of radioactive materials to the environment following a LOCA.
The system accomplishes this function through the use of the equipment described in Section 6.7.2.
IMBbXlHATEY]
IC M
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The manual initiation of/the system be carried out withi W 20 minutes following:-- accicene, provided the setpoints of the
'M DBA-Lo04 ptengasmlare satisfiedf It is possible, due to MSIV closure
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A@ m=5iE PETWAS ACB THE ECG 6*'~8 LE2i' LGVEL.
HCGS FSAR 5/85 sequence, to have high pressure between the inboard and outboard MSIVs.
If such pressure were to exist, there would be no need to activate any portion of'the MSIV sealing system when the pressure between valves is higher than the reactor vessel pressure, since ggggg3 steam trapped between the valves when they closed would. serve as 25 PSG the sealing medium.
Once the pressure hasf;cccjetbuthe MSIV AND sealing system M 6 activated to effect leakage control.
OFMSGG V
7,LOEL 15E)
RaEasss itsAca w EccAUM7 If there is gross leakage from the system, a timer closes the
- USEt, pressure differential control valve.
The system would then be manually secured by the operator.
Thus, the system detects high main steam line pressure and prevents system actuation.
It also prevents excessive MSIV or main steam line leakage through the automatic closure of the pressure differential control valve by the timer.
- Thus, containment pressurization is precluded.
The dose contribution of the main steam lines, considering the MSIV sealing system, is evaluated in Section 15.6.
n 6.7.3.6 Failure Mode and Effects Analysis The consequences of component malfunctions are shown in Table 6.7-1.
The failure modes and effects analysis of the MSIV sealing system instrumentation is discussed in Section 7.3.2.
6.7.3.7 Influence on Other Safety Features The MSIV sealing system is powered from the_ Class 1E power sources.
The load is estimated to be about 40 kW.
- -(The leakage from the inboard MSIVs is discussed in Section 6.2.5.
g
- ejassumedtoleakatn\\rateofFTIEhsefh.
sacr me v In addition, gases, does not introduce or expose the steam piping or thethis system, by exhaus srg s uNES valves to thermal or mass loadings different from those ARE experienced in normal. isolation valve service and therefore cannot affect or degrade the sealing ability of the MSIVs.
6.7-9 Amendment 10
HCGS FSAR 5/85 6.7.3.8 Radiological Evaluation The activity released to the environment through the inboard MSIV leakage, and the resulting offsite dose consequences, are evaluated in Section 15.6.5.
6.7.4 INSTRUMENTATION REQUIREMENTS The instrumentation necessary for control and status indication of the main steam isolation valve (MSIV) sealing system is classified as essential.
It is designed and qualified, in accordance with applicable IEEE standards, to function under Seismic Category I andfLOCA environmental loading conditions lDW4 1 appropriate to its installation with the control circuits designed to satisfy the mechanical and electrical separation criteria.
See Section 7.3.1 for a control and instrumentation description.
6.7.5 INSPECTIONS AND TESTING
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Preoperational tests for the MSIV sealing system are discussed in Chapter 14.
During normal plant operation, the main steam isolation valve (MSIV) sealing system can be tested.
A simulated reactor pressure vessel (RPV) pressure signal is introduced from the control equipment room in place of the pressure transmitter output from the RPV.
This actuates the pressure differential control valve, admitting gas from the gas receiver.
Gas passes through the flow elements, then through the 1-inch test line and back to the primary containment gas compressor suction, or to the drywell when the compressor is not working.
This will verify the modulating pressure differential control valve operation, and whether or not the flow element and other components in the test line they are functional.
The containment isolation valves are closed during these tests.
Tests are conducted for complete functioning of the whole system during extended plant shutdowns or refueling.
An actual signal output from the RPV can be used to verify the operability of controls and the actuating devices in the MSIV sealing system.
(.
x 6.7-10 Amendment 10
(
1 With the pressure transmitter isolated from the RPV, overlap testing can be performed after shutdown with the primary pressure still above the setpoint.
Following the performance of the local leak rate test of the main steam lines, a mathematical correction will be made to the sum of the leak rates for all four lines in order to account for the density effects between the test pressure and operational pressure.
A density correction must be made since a higher mass flow rate (i.e.
higher leakage) exists at the systems maximum operational pressure (25 psig).
The LLRT results will be multiplied by a density correction factor of 1.48 (see the calculational summary contained in Reference 6.7-1), and compared to the combined
~
46 scfh acceptance criteria for all four main steam lines i
(Technical Specification 3.6.1.2).
6.
7.6 REFERENCES
6.7-1 Letter from PSE&G (C.A. McNeill) to the NRC'(E.
Adensam), " Main Steam Isolation Valve Sealing System",
dated March, 1986. - Calculation of the LLRT Correction Factor Utilized When Determining the Leakage Rate Through the Main Steam Lines.
l l
I i
i i
s 4
6.7-11
('
a c.
Leakage from the main steam isolation valve sealing system (MSIVSS).
\\It is assumed that the MSIVs will leak at a[ rate of 46 SCFH Olb.707 cfr ( 11. 5 Cri for each Of the f cur valvcs; for noe AOL the first 20 minutes of the accident.
At that time, hyse operator action to initiate the MSIVSS will eliminate MAW S&V1 further leakage.
As discussed above, after the initial DiJGS 175 seconds, the leakage is released to the reactor building.
The iodine is assumed to be 91% elemental, 5% particulate, and 4% organic.
The FRVS will maint'ain the reactor building at a negative pressure (-0.25 inch w.g.) by exhausting air according to the following equation:
E(t) = 336 + 5637 exp. (-1.18t) l where:
E(t) = exhaust rate, cfm t
= time after the building reaches -0.25 inch w.g.,
h (assumed to be 175 s after LOCA) l j
The FRVS provides for filtered recirculation and filtered exhaust.
A description of the FRVS design is provided in Section 6.8.
A discussion of the mathematical modeling of the FRVS is in Section 15A.6.2.
Fission product activity airborne in the reactor building and the activity released to the environment based on the above assumptions are given in Tables 15.6-15 and 15.6-16, respectively.
15.6.5.5.1.3 Radiological Results Dose conversion factors for iodine are taken from Regulatory Guide 1.109 and breathing rates during the accident are taken from Regulatory Guide 1.3 as presented in Appendix 15A.
The whole body-dose is calculated using the dose conversion factors for the semi-infinite cloud model discussed in Regulatory Guide 1.109.
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15.6-20 Amendment 7 A