ML15224B185
| ML15224B185 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse, Oconee, Arkansas Nuclear, Crystal River, Rancho Seco, Bellefonte, 05000000, Crane |
| Issue date: | 05/11/1988 |
| From: | Dudley R Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8805250003 | |
| Download: ML15224B185 (14) | |
Text
p~ REc3Z 0 aUNITED STATES S,
NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 May 11, 1988 Docket Nos. 50-313/438/439/302/346/
269/270/287/312 and 289 LICENSEES:
LISTED BELOW FACILITIES:
Arkansas 1; Bellefonte 1 & 2; Crystal River 3; Davis-Besse; Oconee 1, 2, 3; Rancho Seco and Three Mile Island
SUBJECT:
SUMMARY
OF MAY 5, 1988 MEETING REGARDING A NON-CONSERVATIVE ASSUMPTION IN THE APPROVED B&W ECCS EVALUATION MODEL On May 5, 1988 a meeting was held in Rockville, Maryland between members of the NRC staff and the B&W Owners Group (BWOG) representing the licensees of the above facilities. The purpose of the meeting was to inform the NRC of a non-conservative assumption contained in the approved B&W ECCS evaluation model. Attendees at the meeting are shown in Enclosure 1. Slides used by the B&W Owners Group are provided in Enclosure 2.
The BWOG stated that the current B&W ECCS model does not consider steam condensation in the downcomer region of the core. Recent B&W workhas shown that condensation would occur and would cause reduced core reflooding rates which would result in increased peak cladding temperatures. B&W added a steam condensation model to the presently accepted code and calculated for certain scenarios that the new phenomenon could increase peak clad temperature by as much 257 0F and could result in the final temperature exceeding the acceptable limit of 2200'F. However, the BWOG stated that other recent code refinements had been made to separately model core and bypass flow during the reflooding period. These refinements increase the core reflooding rate and result in lower peak clad temperatures. The BWOG stated that the combined effect of these two model changes would have a net result of lowering the peak clad temperature. The Owners Group concluded that the currently approved Evaluation Model still conservatively predicts peak clad temperature and that there was no safety concern regarding the current model.
The BWOG stated that additional code development and application studies were planned to confirm the above conclusion.
The NRC stated that further information was required before the staff could evaluate the BWOG's preliminary conclusion. The staff requested that the BWOG provided this information by approximately June, 1988. The staff requested 8805250OO3 s80511 PDR ADOCK 05000269 P
.0 2 -
May 11, 1988 that the BWOG promptly provide a letter documenting their plans and schedules. The staff requested and the BWOG agreed to immediately notify the NRC if any BWOG follow-on work produces results which would contradict the BWOG conclusions provided at the meeting.
/s/RDudley Richard F. Dudley, Technical Assistant for Division of Reactor Projects -
- III, IV, V and Special Projects
Enclosure:
- 1. Meeting Attendees
/DRSP D/DR RDudley:ps G4la n
5/ 0/88 5/1 /88
ENCLOSURE 1 ATTENDANCE -
B&W OWNERS GROUP MEETING WITH NRC -
MAY 5, 1988 RE: ECCS EVALUATION MODEL Name Organization R. Dudley NRC/DRSP P. Guill Duke Power R. Schomaker B&W A. Irani GPU Nuclear J. Paljug B&W G. Schwenk NRC/SRXB G. Holahan NRC/NRR H. Silver NRC/NRR CR-3 PM H. Berkow NRC/NRR D. Hood NRR/PD 2-3 F. Orr NRR/PD 1-4 R. Hernan NRR/PD 3-3 (TMI-1 PM)
J. Giitter NRR/PD 3-3 (Davis-Besse)
J. Stolz NRR/PD 1-4
ENCLOSURE 2 BWOG/NRC MEETING - REFLOD3 MODEL MAY 5, 1988 AGENDA PURPOSE OF MEETING P. GUILL PRESENTATION OF REFLOD MODEL R. SCHOMAKER BACKGROUND EM CHANGES RESULTS DISCUSSION ALL NRC CAUCUS/CONCLUSIONS NRC
EVALUATION OF POTENTIAL CONCERNS WITH B&WOG LARGE BREAK LOCA EVALUATION MODEL CODE REFLOD3 -
BACKGROUND O
DURING THE B&W EVALUATION OF REFLOODING CHARACTERISTICS ON A WESTINGHOUSE APPLICATION, THE INFLUENCE OF CONDENSATION IN THE DOWN COMER REGION WAS BEING INVESTIGATED.
O IT WAS DETERMINED THAT THIS PHENOMENA WOULD HAVE AN IMPACT ON REFLOODING RATES.
O PREVIOUSLY THIS PHENOMENA WAS CONSIDERED TO HAVE MINIMAL EFFECT AND THEREFORE NOT MODELED IN REFLOD3 CODE.
0 IT WAS NOTED THAT STEAM CONDENSATION ON LPI IN THE UPPER DOWNCOMER REGION DURING THE CORE REFLOODING PHASE OF A LARGE BREAK LOCA WAS NOT ACCOUNTED FOR IN THE B&W MODEL.
QUALITATIVE CONCERN 0
CONDENSATION WOULD LOWER THE PRESSURE IN THE PRIMARY SYSTEM DURING REFLOODING RESULTING IN A HIGHER SPECIFIC VOLUME OF STEAM THROUGH THE REACTOR VENT VALVES AND PRIMARY PIPING.
O HIGHER SPECIFIC VOLUME CAUSES INCREASED RESISTANCE TO STEAM FLOW WHICH RESULTS IN DECREASED CORE FLOODING RATES.
O REDUCED FLOODING RATES RESULT IN INCREASED PEAK CLAD TEMPERATURES.
0 CONCERN THAT PCT'S MAY BE UNDERESTIMATED. -
PSC FILED MARCH 1986
EVALUATION PROCESS o
ADDED A STEAM CONDENSATION MODEL TO THE PRESENT ACCEPTED REFLOD3 CODE o
EVALUATED CHANGE IN PCT FOR VARIOUS ELEVATIONS o
NOTED ALSO A CONSERVATISM IN B&W REFLOD MODEL WITH RESPECT TO THE MODEL USED FOR WESTINGHOUSE ANALYSES SPLIT OF FLOW AREAS FOR CORE AND CORE BYPASS o
EVALUATED THE IMPACT OF FLOW SPLIT MODELING ON PCT FOR THE WORST LOCATION CONCLUSION o
PEAK CLAD TEMPERATURE PREDICTED BY THE PRESENTLY ACCEPTED EM IS CONSERVATIVE WITH RESPECT TO THE USE OF THESE MODEL CHANGES.
PEAK CLAD TEMPERATURE COMPARISON LOWERED LOOP PLANTS PCT*
PCT ELEVATION W/O CONDENSATION W/ CONDENSATION D
4' 1943 2022
+ 82 6'
2108 2365
+257 8'
1959 2141
+182 10' 1757 1844
+ 87 RAISED LOOP PLANT PCT*
PCT ELEVATION W/O CONDENSATION W/ CONDENSATION D
6' 1950 2056
+106
- CALCULATION BASED ON PRESENTLY ACCEPTED EM
REFLOD3 -
CORE/CORE BYPASS MODEL 0
CURRENT TREATMENT (COMBINED FLOW AREA) UNDERESTIMATES CORE FLOODING RATE 0
CORE AND BYPASS EXPERIENCE DIFFERENT T-H CONDITIONS DURING REFLOODING 0
WHEN MODELED SEPARATELY, FLOODING THROUGH CORE INCREASES RESULTING IN SIGNIFICANTLY LOWER PEAK CLAD TEMPERATURES.
PEAK CLAD TEMPERATURE COMPARISON LOWERED LOOP PLANTS PCT*
PCT ELEVATION W/O CONDENSATION WI CONDENSATION D
4' 1943 2022
+ 82 6'
2108 2365
+257 8'
1959 2141
+182 10' 1757 1844
+ 87 RAISED LOOP PLANT PCT*
PCT ELEVATION W/O CONDENSATION W/ CONDENSATION D
6' 1950 2056
+106 LOWERED LOOP PCT W/ CONDENSATION ELEVATION AND SPLIT CORE/BYPASS 6'~
2050 D -315
- CALCULATION BASED ON PRESENTLY ACCEPTED EM
CONCLUSION 0
PRESENT EVALUATION MODEL PRODUCES A CONSERVATIVE PREDICTION OF PEAK CLAD TEMPERATURE -
THEREFORE, THERE IS NO SAFETY CONCERN
FUTURE ACTIVITIES COMPLETE EVALUATION OF JUNE 1988 CONDENSATION AND CORE/
CORE BYPASS EFFECTS RAISED LOOP ANALYSIS (CY7) 1989 OF LHR LIMITS AT ALL ELEVATIONS CONFIRM APPROPRIATE MODELS FOR IMPLEMENTATION IN REFLOD3 INSTALL & VERIFY PERFORMANCE OF REFLOD3 CONFIRMATION OF PRELIMINARY EVALUATION RESUBMIT REFLOD3
\\,,go iet 313/438/439/346/269/270 287/312 and 289 NRC & Local PDRS D. Crutchfield R. Dudley G. Holahan OGC - Bethesda E. Jordan J. Partlow ACRS 10 H. Clayton J. Clifford B. Troskoski M. Johnson T. Martin G. Schwenk H. Silver H. Berkow D. Hood F. Orr R. Hernan J. Giltter J. Stolz