ML20209A796
| ML20209A796 | |
| Person / Time | |
|---|---|
| Site: | South Texas  |
| Issue date: | 01/21/1987 |
| From: | Kadambi N Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8702030444 | |
| Download: ML20209A796 (49) | |
Text
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3RN 21 m-Docket Nos.: 50-498 and 50-499 APPLICANT: Houston Lighting and Power Company FACILITY: South Texas Project Units 1 and 2
SUBJECT:
SUMMARY
OF MEETING ON BORON DILUTION ANALYSIS ON OCTOBER 30, 1986 The meeting was held to discuss the submittal by the applicant dated September 30, 1986 and entitled "Probabilistic Boron Dilution Analysis". Enclosure 1 shows the meeting attendees. Enclosure 2 provides the slide and other information received by the staff.
Discussion The applicant provided information to justify their portion that the report of September 30, 1986 is infact a determinatic evaluation and does not use probabilistic methods for licensing.
i N. P. Kadambi, Project Manager PWR Project Directorate No. 5 Division of PWR Licensing-A
Enclosures:
As stated Distribution C;Diciel:F11e? M
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NRC PDR' Local PDR PD#5 R/F J. Partlow V. Noonan H. Kadambi OGC-Bethesda E. Jordan B. Grimes ACRS (10)
M. Rushbrook PD#5 DIR:PD#5 NKadambi:ss VSNoonan 1/)A/87 1/ /87 8702030444 EF70121 PDR ADOCK 05000498 4 PDR
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Docket Nos.: 50-498 and 50-499 APPL.ICANT: Houston 1.ightino ard Power Company FACII.ITY: South Texas Pro. ject Units 1 and ?
SUBJECT:
SUMMARY
OF MEETING ON 1.ONG TERM C001.ING AND BORN DII.UTION ANAI.YSIS, JANUARY 16, 1987 The meetino was held to discuss the applicant's resolution of certain questions raised by the staff regarding the applicant's submittals on these sub.iect. Enclosure 1 shows the meeting attendees, Enclosure ? provides the hand-outs and visual-aids used at the meetino.
Discussion The applicant. submitted on September 30, 1986 responses to Open items 15 and 16 of the SER on the above sub.jects. Subseouent telephone conversations with the applicant led to the staff ouestionino the comparison of the results from the codes TREAT and NO TRUMP, the predictions for natural circulation cooldown, and the accounting of upper head volume in the boron dilution analysis.
Durino the meeting, the applicant showed that the results from TREAT and NOTRUMP are comparable with a time displacement of some of the predicted phenomena. The divergence of data in the earlier submittal was satisfactorily explained.
The question raised by the staff on the natural circulation cooldown concerned the proper procedure to be used by the operator so as to preclude formation of a bubble in the head. The applicant presented the results of analyses which show that, even under conservative assumptions, the operator could use the '
upper head thermocouples to preserve adequate subcooling. If the subcooling decreased below (10*F ' Uncertainty) the head vent would be used to prevent bubble formation. The applicant made a commitment to include this procedure for use by the operator if and when needed.
The applicant informed the staff that no presentation was available on the boron dilution analysis question due to a delay in completing the calculations. The reouired results would be available in early to mid-February and submitted for staff review at that time.
Ww- Y '.
N. P. Kadambi, Project Manaaer PVR Pro.iect Directorate No. 5 Division of PWR I.icensing-A
Enclosures:
As stated
, ) '
MEETING ON LONG TERM COOLING & BOP 0N DILUTION JANUARY 16, 1987 N. P. Kadambi NRR/PD#5 B. Mann NRR/RSB L. Schlazer HL&P W. R. Spezialetti W J. S. Phelps HL&P Licensing A. C. Cheung W Nuclear Safety Jack Bailey HL&P PE Licensing Mark Wisenburg HL&P Deputy Project Mgr.
Larry Bell NRC/RSB/PWR-A Bruce Lorenz W. Licensing Jack Reck W Nuclear Safety Rick Ofstun W Nuclear Safety Eric Frantz W Nuclear Safety Walton Jensen NRC/ PARS e
l ie-s- + - , - . . - - -, _w -- .--- , - - - , - , -- --- ,--r - - , -- . ,, _ . , - , , -, .
o e Mr. J. P. Goldberg Houston lighting and Power Company South Texas Project i
cc:
Brian Berwick, Esq. Resident Inspector / South Texas Assistant Attorney General Project Environmental Protection Division c/o U.S. Nuclear Regulatory Commission P. O. Box 12548 P. O. Box 910 Capitol Station Bay City, Texas 77414 Austin, Texas 78711 Mr. Jonathan Davis Mr. J. T. Westermeir Assistant City Attorney Manager, South Texas Project City of Austin Pouston lighting and Power Company P. O. Box 1088 P. O. Box 1700 Austin, Texas 78767 Pouston, Texas 77001 Ms. Pat Coy Mr. H. L. Peterson Citizens Concerned About Nuclear Mr. G. Pokorny Power City of Austin 5106 Casa Oro P. O. Box 1088 San Antonio, Texas 78233 Austin, Texas 78767 Mr. Mark R. Wisenberg Mr. J. B. Poston Manager, Nuclear licensing Mr. A. Von Rosenberg Pouston lighting and Power Company City Public Service Boad P. O. Box 1700 P. O. Box 1771 Fouston, Texas 77001 San Antonio, Texas 78296 Mr. Charles Halligan Jack R. Newman, Eso. Mr. Burton L. Lex Newman & Poltzinger, P.C. Bechtel Corporation 1615 l Street, NW P. O. Box 2166 Washington, D.C. 20036 Pouston, Texas 77001 Melbert Schwartz, Jr., Esq. Mr. E. R. Brooks Baker & Botts Mr. R. L. Range One Shell Plaza Central Power and light Company Houston, Texas 77002 P. O. Box 2122 Corpus Christi, Texas 78403 '
Mrs. Peggy Buchorn Executive Director .
Citizens for Equitable Utilities, Inc.
Route 1, Box 1684 Brazoria, Texas 77422 W
3
f Houston lighting & Power Company - 2- South Texas Pro. ject cc:
Regional Administrator, Region IV U.S. Nuclear Regulatory Commission Office of Executive Director for Operations 611 Ryan Plaza Drive Suite 1000 Arlington, Texas 76011 Mr. lanny Sinkin, Counsel for Intervenor -
Citizens Concerned about Nuclear Power, Inc.
Christic Institute 1324 North Capitol Street Washington, D.C. 20002 Licensing Representative Houston lighting and Power Company Suite 1309 7910 Woodmont Avenue Bethesda, Maryland 20814 f
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TREAT /NOTRUMP SMALL BREAK LOCA COMPARIS0N FOR SOUTH TEXAS LONG TERM COOLING REC 0VERY ANALYSIS A
PRESENTATION TO THE NRC A
BY RICK P. 0FSTUN WESTINGHOUSE NUCLEAR SAFETY DEPARTMENT OPERATIONAL SAFEGUARDS ANALYSIS JANUARY 16, 1987 f
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o 0BJECTIVE OF COMPARISON TO DEMONSTRATE THE APPLICABILITY OF THE TREAT CODE TO CONSERVATIVELY MODEL SMALL BREAK LOCA AND LONG TERM COOLING REC 0VERY W/0 CORE UNC0VERY o HOW WAS THIS ACCOMPLISHED?
MODELS OF THE SOUTH TEXAS PLANT WERE CREATED FOR BOTH TREAT AND NOTRUMP AND A 1.5 INCH LOCA TRANSIENT WITH OPERATOR C00LDOWN WAS SIMULATED WITH BOTH CODES REVIEW 0F COMPLIANCE STATUS OF TREAT MODELS AGAINST APPENDIX K FOR ANALYSIS OF SMALL BREAK LOCA WITHOUT CORE UNC0VERY o RESULTS WERE PRESENTED IN WCAP-11232
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m e - , - . .,-,-- - - -- - _ - , , , , ,, w - ... _-, _.-.. . - - , , . - --- - , - _ - -
o o COMPARISON SHOWS TREAT CORRECTLY PREDICTS THE TRENDS OF ALL IMPORTANT PARAMETERS o DIFFERENCES IN THE FOLLOWING VARIABLES WERE QUESTIONED BY THE NRC:
- 1. SG SECONDARY LEVELS
- 2. SG TUBE LEVELS
- 3. CORE INLET FLOW
- 4. HOT LEG FLOWS
- 5. SECONDARY STEAM FLOW
- 6. COLD LEG TEMPERATURES
- 7. DOWNCOMER TEMPERATURES o . WESTINGHOUSE WAS ASKED TO EXPLAIN WHETHER THIS DIVERGENCE WOULD CONTINUE AND TO JUSTIFY THE CONSERVATISM 0F THE TREAT SBLOCA ANALYSIS
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APPROACH o DESCRIBE DIFFERENCES BETWEEN THE 2 CODES WHICH COULD CAUSE THE APPARENT DIVERGENCE.
o DESCRIBE DIFFERENCES IN THE THERMAL-HYDRAULIC TRANSIENT WHICH LED TO THE APPARENT DIVERGENCE, o EXTEND THE TREAT ANALYSIS AN ADDITIONAL 600 SEC TO SHOW THAT THE DIVERGENCE WOULD NOT CONTINUE.
o DISCUSS IMPACT AND SIGNIFICANCE OF REMAINING DEVIATIONS ON LONG TERM COOLING.
i o MODELLING DIFFERENCES BETWEEN TREAT AND NOTRUMP SG SECONDARY N0 DING (SINGLE VS MULTI-NODES)
INTERFACE C0P. RELATIONS (BUBBLE RISE, HEAT AND MASS TRANSFER) 2-PHASE FLOW CORRELATIONS (DRIFT FLUX, FLOODING) o TRANSIENT BEHAVIOR DIFFERENCES PREDICTED BREAK FLOW SLIGHTLY HIGHER IN NOTRUMP DUE TO SUBC00 LING DRAINING BEHAVIOR AND MASS DISTRIBUTION AFFECTED CAUSES SHIFT IN TIME NATURAL CIRCULATION IS LOST l
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O CONCLUSIONS:
TREAT IS FOUND TO COMPLY WITH APP K MODEL REQUIREMENTS IN AREAS THAT HAVE IMPACT ON SBLOCA WITHOUT CORE UNC0VERY.
COMPARIS0N WITH NOTRUMP SHOWS TREAT CORRECTLY PREDICTS THE TRENDS AND T/H PHENOMENA 0F TRANSIENT.
REMAINING DIFFERENCES ARE EXPLAINED BY DIFFERENT .
MODELLING TECHNIQUES BETWEEN THE 2 CODES, I.E., THE DRAINING OF THE STEAM GENERATOR U-TUBES AND RESULTING
, LOSS OF NATURAL CIRCULATION ARE SHIFTED IN TIME.
THE TRANSIENT CHARACTERISTICS PREDICTED BY EACH CODE ARE THE SAME, I.E., 2-PHASE FLOW, LOSS OF NATURAL CIRCULATION, LOOP ASYMETRY, ETC. THE LONG TERM COOLING REC 0VERY ACTIONS, WHICH ARE SYMPT 0M BASED, COULD BE SLIGHTLY SHIFTED IN TIME BUT WILL REMAIN THE SAME.
THE TREAT CODE HAS THE NECESSARY AND REQUIRED MODELS TO MODEL A SMALL BREAK LOCA LONG TERM COOLING REC 0VERY TRANSIENT WITHOUT CORE UNC0VERY.
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NRC Question on WCAP 11232, comoarison of the TREAT and NOTRUMP Small Break LOCA Transient Results Some of the figures in this report show significant divergence between TREAT and NOTRUMP results at the end of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, e,g. figures for SG level (both primary and secondary), core inlet flow.(TREAT results are more optimistic than NOTRUMP, ditto for hot leg flow),
secondary steam flow, cold leg and downconer temperatures. Explain whether this divergence will persist for the remainder of the analysis and justify the conservatism of the TREAT SBLOCA analysis.
Response
To show that the divergence does not continue, the TREAT analysis was extended an additional 600 seconds. The figures noted above which show apparent divergence will be described separately below. To help understand the causes of the apparent divargence, the differences in modelling techniques and the resultant transient behavior have been detailed below.
Differences in Modellina Techniaues The steam generator modeling for TREAT and NOTRUMP is different.
TREAT uses multiple nodes to represent the steam generator secondary system, NOTRUMP uses a single non-equilibrium node. The level in TREAT is based on the level in the low void fraction downcomer region to simulate the actual level taps in the plant. After reactor trip and the recirculation model is turned off, this level would be expected to be lower than the level based on the single node NOTRUMP steam generator with a higher averaged void fraction. The deviations are more pronounced at lower steam generator levels where the
, downcomer annulus area is small. Note, although the calculated mixture levels may be slightly different due to the difference in average void fraction, the secondary mass should be nearly the same.
The models for the bubble rise, drift flux and flooding correlations affect both the mixture level and inter-node flow calculations. The drift flux and flooding models control the mass distribution between '
nodes during 2-phase flow conditions. The bubble rise model -
determines the phase separation within each node.
The NOTRUMP models for these correlations are more sophisticated than the TREAT models. NOTRUMP, which runs in batch mode, is able to spend more time computing the coefficients for these correlations.
The TREAT code, which is interactive, must run in real-time. To do this, TREAT must complete all of its calculations with a fixed time step size. It cannot afford to spend a large amount of computation time calculating the coefficients for these correlations. Therefore, the models for these correlations have been simplified to reduce the computation time.
Differences in Thermal-Hydraulic Behavior Most of the differences in thermal-hydraulic behavior can be tied to i the difference between the TREAT and NOTRUMP break flow rate. While TREAT and NOTRUMP both use the same break flow correlations, due to slightly higher predicted RCS pressure and subcooling at the break i location, NOTRUMP predicts a slightly higher break flow than TREAT between 500 and 3000 seconds in the transient. This causes the SG tubes to drain later and natural circulation to continue for a longer period of time in the TREAT analysis.
After 3200 seconds, the TREAT break flow begins to exhibit the same behavior NOTRUMP had shown between 2200 and 3000 seconds, i.e., an oscillatory behavior caused by the break passing between subcooled and saturated fluid flow. The increase in the TREAT break flow causes the fluid inventory to begin decreasing more rapidly. The SG :
tubes begin to drain and natural circulation flow is reduced. !
Extended Comoarison Plots -
As mentioned above, the difference in the integrated break flow causes earlier draining of the SG tubes and subsequent, loss of natural circulation in the NOTRUMP analysis'.'.This causes the plots.
of the SG tube sixture level, hot leg and; core flowrates and cold leg '
! ' fluid temperatures to apparently diverge at the end of the 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> comparison. To show that the results do not actually diverge and that a similar draining phenomena will occur with TREAT, the TREAT analysis was extended an additional 600 seconds. The comparison
. plots are presented in the following figures. Each plot will be
- described separately below.
Figures 4-2-14 and 15 - SG Levels (Secondary) i The steam generator modeling for TREAT and NOTRUMP is different as explained above. This is the reason for the apparent divergence in loop 1 secondary mixture level. Loop 2 mixture level is maintained near the NOTRUMP value for the comparison. The difference in loop 1 SG secondary mixture level is not important for the long-term cooling analysis since, by the conservative assumptions made in the analysis, this steam generator is incapable of removing heat.
Figure 4-2 SG 2 Uphill Tube Mixture Level At the and of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, the TREAT uphill steam generator tube level shows a rapid drop. As can be seen in Figure 4-2-11, this is really the beginning of a mixture level oscillation which oscillates between 67 and 71 feet and averages around 69 feet. The NOTRUMP level at 4
this time is around 71.5 feet. The slightly lower level calculated
- s by TREAT'is caused by differences in the bubble rise modelling and the integrated break flow which have affected the mixture distribution in the steam generator tubes. This small difference in the SG tube mixture level after loop stagnation will not affect the predicted SG heat removal significantly and therefore is not I important for the long term cooling analysis.
\
i
Figure 4-2 SG 2 Downhill Tube Mixture Level The extended TREAT analysis shows the downhill mixture level continues to drop and is approaching the corresponding NOTRUMP level after the additional 600 seconds. The delay in draining the downhill SG tubes is due to the difference in integrated break flow which has affected the system mass inventory. Both codes predict draining of the SG tubes and subsequent reduction in loop flow, but at slightly different times.
Figure 4-2 Reactor Vessel Inlet Flow The 2 variables plotted in the WCAP for core inlet flow did not represent the same thing. The correct TREAT variable has been plotted in this copy. As can be seen, the vessel inlet flows compare fairly well. Both the TREAT and NOTRUMP analyses show core decay heat can be removed with the available flow, therefore long term core cooling capability has been demonstrated.
Figure 4-2 Loop 2 Hot Leg Flow At the and of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, the loop 2 hot leg flow was just beginning to oscilate and so appeared to be diverging from the NOTRUMP result.
The extended plot shows the average of the oscilation is roughly the same as the value predicted by NOTRUMP at the and of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
Figure 4-2 Loop 3 Hot Leg Flow At the end of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, the loop 3 hot leg flow was decreasing rapidly just as natural circulation was lost. The extended plot shows the flow changes between steam and 2-phase liquid throughout the additional 600 seconds. The NOTRUMP data appears to be continuous 2-phase flow at the end of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The differences in the calculated flow rate and flow void fraction appear to be caused by the differences in the drift flux and/or bubble rise models between the 2 codes. Both codes will predict loop flow stagnation.
Figure 4-2 Secondary Steam Flow To match the SG mixture levels, the auxiliary feedwater delivered in the TREAT analysis was intentionally set higher during the first 2500 seconds. The energy transferred from the RCS to the steam generators remained the same for both analyses. However, energy which produced steam in the NOTRUMP analysis acted to increase the temperature of the subcooled feedwater in the TREAT analysis resulting in lower PORV flow rates predicted by TREAT. This is the reason for the difference in secondary steam flow.
Figure 4-2-34 to 36 - Cold Leg Temperatures Loop 1 and 2 cold leg temperatures were similar to the NOTRUMP results (within 20 degrees at the end of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />) .
a
The TREAT loop 3 cold leg temperature is substantially higher than the corresponding NOTRUMP result. The higher loop flow rate predicted by TREAT (prior to loss of natural circulation at the end of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />) allows the cold SI water to mix with warm water from the i rest of the RCS and keeps the cold leg temperature high. _The extended plot shows that as the flow in loop 3 decreases following ;
the loss of natural circulation, the cold leg temperature drops which agrees with the NOTRUMP calculation.
Figure 4-2 Downconer Temperature The TREAT downconer temperature is influenced by the warmer fluid in loops 2 and 3. The extended plot shows that when loop 3 cold leg temperature drops, the downcomer temperature drops as well. The slightly higher TREAT predicted downconer temperature has no significant impact on the long term recovery analysis since both codes would predict the symptoms required for a PTS soak which are based on the cold leg temperature indication during the recovery procedure.
Conclusion The transient results presented in the TREAT /NOTRUMP comparison report which appear to diverge at the end of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> can be traced to
- differences in the modelling techniques and resulting transient l behavior. The modelling differences between the 2 codes cause the i calculated break flow to be slightly different during the early part j of the analysis which results in an earlier draining of the SG tubes in NOTRUMP. This slightly different mass inventory and mass distribution in the 2 models explains the apparent divergence in mixture levels, flow rates and temperatures at the end of 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
When the TREAT analysis was extended an additional 10 minutes, the earlier draining phenomena predicted by NOTRUMP was observed with TREAT.
From a long term cooling standpoint, the 10 minute difference in the computed time of SG tube draining and subsequent loss of natural circulation break flow has an insignificant effect on the actual cooldown analysis which lasts about 10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br />. TREAT predicts the I
l same trends in thermal-hydraulic behavior as NOTRUMP, therefore, the symptom based operator actions would be expected to be the same during the long term cooling scenario.
Based on the comparison results reported in WCAP-ll232 and the additional extended TREAT analysis results presented here, it has been demonstrated that TREAT has the necessary and required models and is applicable for analyzing the small break LOCA with long term cooling recovery transients which do not uncover the core.
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- Time (sec)
South Texas 1.5 Inch LOCA Comparison Figure 4-2-35. Cold Leg No. 2 Temperature
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EVALUATION OF USE OF HEAD VENT PATH FOR UPPER HEAD
' C00LDOWN IN STP LONG TERM COOLING PRESENTED T0 i
i US NRC JANUARY 16, 1987 4
f i BY 4
]
~
AUGUSTINE C. CHEUNG MANAGER, OPERATIONAL SAFEGUARDS ANALYSIS NUCLEAR SAFETY DEPARTMENT *
,i
! WESTINGHOUSE ELECTRIC CORPORATION i
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, , - - . . - - - - - , . - ~ . - - , _ . - ,, -,, , , . , . . - - - _ . . . , . . . - _ , - . - - , - - - - , - , - . - . - - . - . - , - . , -
o NRC QUESTION ON STP LONG TERM COOLING ANALYSIS ,
BASED ON THE NRC CONSULTANT'S (BROOKHAVEN) CALCULATION, THE NRC ASKED CAN STP C00L D0WN WITH N0 HEAD SOAK TIME WITHOUT CAUSING A BUBBLE TO FORM IN THE UPPER HEAD.
o TO ADDRESS NRC CONCERN OF UPPER HEAD COOLING WITHOUT CRDM EVALUATE THE USE OF REACTOR VESSEL HEAD VENT TO COOL UPPER HEAD INCORPORATE RECOVERY ACTION INTO C00LDOWN PROCEDURE Os e
MODELING ASSUMPTIONS
- 1. UH FLUID BELOW TOP OF THE GUIDE TUBES IS FULLY MIXED AND THE TREAT PREDICTIONS ARE REPRESENTATIVE OF THE MIXED MEAN TEMPERATURE IN THIS REGION. ,
- 2. TO ADDRESS NRC/BNL CONCERN, THE UH FLUID AB0VE THE GUIDE TUBES IS CONSERVATIVELY ASSUMED TO STRATIFY IN THE ABSENCE OF CRDM FAN COOLERS
- 3. HEAD VENT PATH WILL BE USED TO REMOVE THE UH HOTTER FLUID LAYERS AND PROMOTE MIXING 6
4
~
- 4. HEAT VENT WILL BE OPERATED BASED ON NEASURED SUBC00 LING OF THE HOTTER FLUID IN THE UPPER REGION AS INDICATED BY THE UH TCs.
- 5. FLUID AB0VE THE TOP OF THE GUIDE TUBES IS CONSERVATIVELY ASSUMED TO REMAIN STRATIFIED AND WILL NOT MIX AS IT RISES TO THE TOP 0F THE VESSEL HEAD DURING VESSEL HEAD VENT OPERATION.
- 6. OPERATION OF THE HEAD VENT DURING THE C00LDOWN PERIOD WILL NOT IMPACT OTHER RCS CONDITIONS, (I.E., THE EXISTING STP LONG TERM COOLING ANALYSIS RESULTS WERE USED AS BOUNDARY CONDITIONS)
O
USING HEAD VENT TO PROMOTE HEAD' NIXING AND COOLING o MAINTAIN 10*F SUBC00 LING PLUS UNCERTAINTY IN UPPER HEAD o USE UPPER HEAD THERMOC0UPLE o OPEN HEAD VENT WHEN HEAD SUBC00 LING < 10*F + UNCERTAINTY o CLOSE HEAD VENT WHEN HEAD SUBC00 LING > 20*F + UNCERTAINTY o INCREASE CHARGING TO MAINTAIN HEAD SUBC00 LING e=
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t RESULTS
- 1. UH MAY BE COOLED DOWN BY HEAD VENT OPERATION IN THE ABSENCE OF THE CRDM FAN C0OLERS WITHOUT NEED FOR HEAD SOAKING PERIOD.
- 2. HEAD VENT WAS OPEN FOR APPR0XIMATELY 9.75 HRS DURING THE C00LDOWN PERIOD.
- 3. HEAD VENT OPERATION RESULTED IN THE DISCHARGE OF APPR0XIMATELY 25,000 GALLONS OF FLUID.
- 4. THE VOLUME OF THE FLUID REQUIRED TO MAKE UP FOR HEAD
. VENT DISCHARGES DOES NOT EXCEED THE RWST LIMITS.
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SUMMARY
o FULLY MIXED UPPER HEAD WAS ASSUMED IN THE STP LONG TERM COOLING REC 0VERY ANALYSIS USING THE TREAT CODE o RESULTS OF THIS ANALYSIS SHOWED THAT STP CAN BE COOLED DOWN TO RHR CUT-IN CONDITIONS IN 20.75 HOURS WITHOUT VESSEL HEAD SOAK o ADDITIONAL CONSERVATIVE HAND CALCULATION ASSUMING STRATIFIED FLUID IN THE HEAD WAS PERFORMED o RESULTS SHOWED THAT REACTOR VESSEL HEAD VENT MAY BE OPERATED TO COOL THE UPPER HEAD FLUID WHEN NECESSARY
. o USING THE VESSEL HEAD VENT, STP CAN BE COOLED DOWN TO RHR CUT-IN CONDITIONS IN 20.75 HOURS REGARDLESS OF HEAD MIXING
~
CONDITIONS o OPERATOR ACTIONS TO USE HEAD VENT FOR C0OLING, WHEN .
NECESSARY, WILL BE INCORPORATED INTO STP REC 0VERY PROCEDURE AS CONTINGENCY STEPS 1
o AN ADDENDUM EXPLAINING THE USAGE OF THE HEAD VENT WILL BE l PP.0VIDED AS PART OF THE LONG TERM COOLING REPORT o HLaP WILL CONTINUE TO MONITOR AND EVALUATE THE RESOLUTION
! 0F THIS NRC GENERIC CONCERN
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