ML021650346
| ML021650346 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 05/31/2002 |
| From: | Tuckman M Duke Energy Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML021650346 (9) | |
Text
Duke Energy.
M. S. Tuckman Executive Vice President Nuclear Generation Duke Energy Corporation 526 South Church Street P.O. Box 1006 (EC07H)
Charlotte, NC 28201-1006 (704) 382-2200 OFFICE (704) 382-4360 FAX May 31, 2002 U.
S.
Nuclear Regulatory Commission Washington, D.
C.
20555-001 Attention:
Document Control Desk Subj ect:
References:
Duke Energy Corporation Oconee Nuclear Station, Units 1, 2, and 3 Docket Numbers 50-269, 50-270, and 50-287 Report Pursuant to 10 CFR 50.46, Error Related to Application of the LBLOCA Evaluation Model
- 1) Letter, Framatome ANP to USNRC, "Transmittal of Final Report of PSC 2-00 Related to Core Flood Line Break with 2-Minute Operator ASction Time",
FANP-01-988, April 2, 2001.
- 2) Letter, W. R.
- McCollum, Jr.
(DEC) to USNRC, "Licensee Event Report 269/2001-001, Revision 0",
February 16, 2001.
- 3) Letter, M. S.
Tuckman (DEC) to USNRC, "Report Pursuant to 10 CFR 50.46, Error Related to Application of the SBLOCA Evaluation Model",
November 19, 2001.
10 CFR 50.46 (a) (3)(ii) requires the reporting of changes to or errors in ECCS evaluation models (EM).
This report covers the time period from January 1, 2001 to December 31, 2001.
During this time period, there were two errors reported that were classified as significant changes (APCT > 50 0 F).
The first error is related to Preliminary Safety Concern PSC 2-00 (Core Flood Line Break with 2-Minute Operator Action Time).
The final report summarizing the resolution f 0 0
U. S.
NRC May 31, 2002 Page 2 of this issue was submitted to the NRC in Reference 1. The part-power small break LOCA (SBLOCA) analysis for a core flood tank (CFT) line break with the RCPs tripped at two minutes resulted in a calculated peak cladding temperature (PCT) greater than 22000 F.
The original part-power analysis supported operation with 1 HPI pump unavailable (1 HPI case) and was performed at a power level of 75% of full power (FP).
A licensee event report (Reference 2) was submitted on February 16, 2001 which included a 30 day 50.46 report.
In order to meet the 2200'F 10 CFR 50.46
- criteria, the allowable power was limited to 50% for the 1 HPI case.
The second error is related to a non-conservative initial CFT level assumption.
The correction of this error resulted in an increase of the limiting SBLOCA case PCT by 43 0 F.
This error coupled with three minor PCT reductions, which had been previously identified but not credited, resulted in the absolute value of the PCT changes to exceed 50 0 F.
A 30 day 10 CFR 50.46 report describing this condition was submitted on November 19, 2001 (Reference 3).
During this same period, Oconee implemented Mark-Bll fuel at Units 2 and 3 requiring a reanalysis of the UFSAR Chapter 15 safety analysis.
The Mark-B10T limits were reanalyzed at reduced kW/ft limits to provide more margin to the 2200°F acceptance criterion.
Unit 1 implemented Mark-Bll fuel during calendar year 2000, and now all three units utilize the same LOCA limits.
Included in this report are three summary tables.
Table 1 provides the changes/errors for which a PCT impact has been assessed.
Table 2 presents changes/errors for which no PCT impact has been assessed.
Table 3 provides a summary of the peak cladding temperatures for all three units.
The allowable power level was reduced to 50% FP, for part power conditions (1 HPI case),
to meet the acceptance criteria for a CFT line break with the RCPs tripped at two minutes.
A limited SBLOCA break spectrum was reanalyzed at this power level to provide a basis for future assessments.
The results presented in Table 3 present the limiting case (0.06 ft 2 break) at this power level.
This limited break spectrum accounted for the errors/changes identified in Tables 1 and 2.
The 50% FP analysis is considered a new application and therefore APCT values have not been determined for these analyses.
U.S.
NRC May 31, 2002 Page 3 Please address any comments or questions regarding this matter to Allison J-Young at (704) 382-3154.
Very truly yours, M. S.
Tuckman Attachment xc: Mr.
L.
A.
Reyes Administrator, Region II U.
S. Nuclear Regulatory Commission Atlanta Federal Center 61 Forsyth St.,
SW, Suite 23T85 Atlanta, GA 30303 Mr.
L. N. Olshan U.S. Nuclear Regulatory Commission Mail Stop O-14H25 Washington, DC 20555-0001 Mr.
M. A. Scott Senior Resident Inspector Oconee Nuclear Station
U.S.
NRC May 31, 2002 Page 4 bxc:
L.
F.
Vaughn L.
E. Nicholson M. T.
Cash G.
B.
Swindlehurst R.
C.
Harvey M. E.
Henshaw J.
S.
Warren ELL E-NRC-LOCA
Table 1 Errors / Evaluation Model Changes with PCT Impact Maximum vs. Minimum CFT Water Level Recent SBLOCA sensitivities revealed that the maximum CFT water level assumption would result in higher PCTs than a case assuming the minimum CFT water if the PCT occurs while the CFTs are discharging.
The PCT for the limiting Oconee SBLOCA case occurs while the CFTs are discharging.
Two Oconee SBLOCA cases were analyzed using the void-dependent cross-flow model.
The PCT for the case using the minimum CFT water volume (975 ft 3/tank) is 43 0F greater than when the maximum CFT water volume is used (1085 ft 3/tank).
This PCT increase is considered an estimate since the void dependent cross-flow model was not approved by the NRC when the analysis was performed.
B&W Slug Drag Model Inside the SG Tubes The original SBLOCA spectrum for Oconee was performed without the B&W slug drag model inside the SG tubes.
This model was used in the code benchmark calculations and the EM demonstration cases and should have been used in the Oconee SBLOCA analyses.
When the error was discovered, the worst SBLOCA case was reanalyzed with the drag model corrected and resulted in a decrease in PCT of 140F Water Properties File Changes and Recompiled Code Version Framatome ANP was made aware that INEL made several water property file changes (one correction and several model improvements) in the file used by the RELAP5/MOD-B&W computer code.
These changes were incorporated in a new version of RELAP5 that was compiled on a new HP operating system.
The limiting Oconee SBLOCA was reanalyzed with the new water property file changes and the new operating system and the PCT decreased by 25 0F.
PSC 1-99, Reactor Coolant Pump Type and Two-Phase Degradation Preliminary Safety Concern (PSC) 1-99 dealt with RCP type and two-phase degradation model for large break LOCA (LBLOCA) analyses.
LBLOCA sensitivity studies were used to establish the limiting RCP type (Bingham versus Westinghouse for the Oconee units) and the two-phase degradation modeling (head difference curves and two-phase Table 1 -
1
multiplier) for LOCA applications.
This limiting combination of RCP parameters from the LBLOCA (Westinghouse
- pump, RELAP5 two-phase difference curves with M3-modified head multipliers) was applied to the small break LOCA cases analyzed with loss of offsite power (LOOP).
Reanalysis of the limiting SBLOCA case resulted in a minimal decrease in PCT (5 0F),
because the SBLOCA with LOOP is not a f low dominated transient.
These revised RCP parameters are consistent with the limiting assumptions used for the SBLOCA analyses with delayed RCP trip as documented in the PSC 2-00 analyses.
PSC 2-00(Core Flood Tank Line Break with Offsite Power Available)
Preliminary safety concern (PSC) 2-00 was initiated by Framatome ANP on July 28, 2000.
It identified that the calculated consequences for a postulated core flood tank (CFT) line break could be worse if offsite power were available, with a reactor coolant pump trip at two minutes.
The final summary report for PSC 2-00 was completed on March 30, 2001 (Reference 1).
For Oconee, the CFT line break at full power conditions results in an increase in the calculated PCT, however, the limiting SBLOCA PCT remains the 0.15 ft 2 break with the RCPs tripped on reactor trip (LOOP).
Thus, the PCT for the limiting full power SBLOCA case is not impacted.
Therefore, the PCT impact of this change is estimated to be 0°F.
The Oconee SBLOCA spectrum supporting operation at 75% FP (1 HPI case),
was reviewed with respect to PSC 2-00.
The CFT line break with offsite power available and RCPs tripped at two minutes resulted in a calculated PCT greater than 22000 F.
A licensee event report (Reference 2) was submitted on February 16, 2001 which included a 30 day 50.46 report.
Therefore the net PCT change associated with the resolution of PSC 2-00 for the 75% FP SBLOCA analysis is
> 338°F (2200'F -
1862°F).
The revised part-power analysis (50% FP) demonstrated that the CFT line break with a two minute RCP trip time yields acceptable results (PCT <
2200 0 F).
The CFT line break was shown to not be the limiting case at a power level of 50% FP.
Table 1 -
2
Table 2 Errors / Evaluation Model Changes with no PCT Impact Reduced EFW Flow The full power (FP)
SBLOCA analysis originally modeled a constant emergency feedwater (EFW) flow of 200 gpm to both steam generators or 400 gpm to one steam generator (with the failure of an emergency bus).
In order to account for possible degradation in pump performance, a reduction of EFW flow at pressures above 1000 psia was analyzed/evaluated.
Above 1000 psia, the EFW flow was reduced to 187.5 gpm/SG at 1064 psia, 162.6 gpm/SG at 1123 psia, and 0 gpm/SG at 1178 psia.
The analyses/evaluations have shown that there is no change in the PCT for the 100%
The part-power SBLOCA analysis (1 HPI case) at 75% FP was not reanalyzed for the reduced EFW flow conditions.
The resolution of PSC 2-00 has shown that these analyses are no longer acceptable with a delayed RCP trip (2 minute operator action time).
The revised part-power analyses at 50% FP were performed assuming the reduced EFW flows specified above.
Table 2
Table 3 Peak Cladding Temperature Summary -
Oconee Units 1, 2 & 3 LBLOCA PCT Comments (OF)
Evaluation model
- RELAP5/MOD2-B&W 2037 Mark-Bll (M5),
Analysis of record PCT 16.8 kW/ft 2050 At 6.021 ft elevation Mark-BlOT, 16.8 kW/ft At 4.264 ft elevation Prior errors (APCT)
- 1. None 0
Prior evaluation model changes (APCT)
- 1. None 0
Errors (APCT)
- 1. None 0
Evaluation model changes (APCT)
- 1. None 0
Absolute value of errors/changes for this report (APCT) 0 Net change in PCT for this report 0
Final PCT 2037 Mark-Bll 2050 Mark-BlOT SBLOCA PCT Comments (OF)
Evaluation model
- RELAP5/MOD2-B&W Analysis of record PCT 1369 Full Power 0.15 ft 2
break Prior errors (APCT)
- 1. None 0
Prior evaluation model changes (APCT)
- 1. None 0
Errors (APCT)
-14 estimated
-5 analysis
-25 PCT determined by
- 4. RELAP5 water property and Unix analysis operating system PCT determined by Table 3
analysis Evaluation model changes (APCT)
- 1. None 0
Absolute value of errors/changes for this report (APCT) 87 Net change in PCT for this report
-1 Final PCT 1368 Analysis of record PCT (new 1261 Reduced Power -
50%
application)
FP (1 HPI case)0.06 ft 2 break Prior errors (APCT)
- 1. None 0
Prior evaluation model changes (APCT)
- 1. None 0
Errors (APCT)
- 1. None 0
Evaluation model changes (APCT)
- 1. None 0
Absolute value of errors/changes for this report (APCT) 0 Net change in PCT for this report 0
Final PCT 1261 Table 3