ML20059H332
| ML20059H332 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 10/29/1993 |
| From: | Dennis Morey SOUTHERN NUCLEAR OPERATING CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9311100050 | |
| Download: ML20059H332 (6) | |
Text
southern Nacisar Operating company Post O" ice Box 1295 B,rmingham, Aiabama 35201 Te'ephone (205) 868-5131 l
Southern Nudear Operating Company Dave Morey Vce P'es'de"t Fan y Project the 5%them electric System e
October 29, 1993 Docket Nos. 50-348 10CFR50.46 50-364 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk l
Washington, D.C. 20555 Joseph M. Farley Nuclear Plant Peak Clad Temperature (PCT) Calculation Gentlemen:
Southern Nuclear was recently informed of two Small Break Loss of Coolant Accident (SBLOCA) evaluation model errors in the calculation of PCT for Farley Nuclear Plant Units 1 and 2. Additionally, one change to the SBLOCA evaluation model has been I
identified.10CFR50.46(a)(3)(i) requires the errors and changes be reported to the NRC within 30 days and a proposed schedule for reanalysis be provided or take action to show compliance. The sum of the absolute magnitude of the errors and changes is greater than 313'F; however, the net effect of the errors and changes is at least a 13 F reduction in the SBLOCA PCT for both Units 1 and 2. provides the current SBLOCA PCTs for both Unit 1 and Unit 2. provides additional details on the model errors /model changes.
The Westinghouse Owners Group is reviewing the model error / change issues and possible development of a generic program for resolution. A schedule for resolution will be provided following the completion of the Westinghouse Owners Group review.
Respectfully submitted, (7) 7F
[
D.N. Morey REM:maf PCTERRO1. DOC Attachments l
l cc:
Mr. S.D. Ebneter Mr. T.A. Reed Mr. T.M. Ross l
l 090035 l
.f n'
I 9311100050 931029
^
s\\\\
l PDR ADDCK 05000348 s
l P
\\
v l
1 4
i t
1 i
t Joseph M. Farley Nuclear Plant Units 1 and 2 Peak Clad Temperature for Small Break LOCA Analyses i
t l
Peak Clad Temperature Changes for Small Break LOCA Analyses Unit 1 Unit 2 Total Analysis-of-Record reported by letter 1805 F 1783 F dated March 16,1993 1993 Model Assessments
- 1. Effect of Siin broken loop *
+150
+150
- 2. Effect of improved condensation model*
-150
-150
- 3. Drift flux flow regime errors
- 13
- 13 Licensing Basis PCT 1792*F 1770 F
- Reported to the NRC by Westinghouse letter ET-NRC-93-3971 dated September 21, i
1993.
P
4 Discussion of Small Break LOCA Model Errors /Model Changes
l Discussion of Small Break LOCA Model Errors /Model Changes
[
- 1. Effect of Safety injection in the Broken Loop (+150*F) f Westinghouse recently completed an evaluation of a potentialissue concerning the i
modeling of safety injection (SI) flow into the broken reactor coolant system (RCS) loop for the small break loss of coolant accident (SBLOCA). Westinghouse previously assumed that modeling any Si to the broken RCS loop would result in a lower calculated l
PCT, and, therefore, modeled all the ECCS broken loop branch line to spill the Si to the containment sump. However, when Siis modeled to enter the broken loop, a significant
{
PCT penalty (+150 F) is calculated by the NOTRUMP small break evaluation model.
An analysis by Westinghouse indicates that the penalty occurs as a result of competition between the steam venting out the break and the Si to the broken loop, which also exits through the break. The competition between the steam and Si results in higher RCS l
pressures for the identical core steaming rates. Since the ECCS uses centrifugal pumps, higher RCS pressure results in lower delivered Si flow rates to the intact RCS loops, leading to a 150 F PCT penalty for both Farley units.
The effects of Si in the broken loop have been determined to not change RCP trip symptoms developed in response to Generic Letters83-10C and 85-12 or Si termination criteria found in the Westinghouse Owners Group Emergency Response Guidelines.
This issue was initially reported to the NRC in Westinghouse letter ET-NRC-93-3971 dated September 21,1993.
i
- 2. Effect ofimproved Condensation Model(-150*F)
When a new conservative model based on prototypic testing was used which modeled I
l the configuration of the Si piping to the RCS cold leg in a Westinghouse designed PWR, a net PCT benefit was calculated. Improved condensation of the loop steam in the intact j
loops results in lower RCS pressure and larger Si flow rates. The increase in Si flow rates, due to lower RCS pressure, leads to the lower calculated PCT.
l The improved condensation model is based on data obtained from the COSI test facility.
The COSI test facility is a 1/100 scale representation of the cold leg and Si injection ports in s Westinghouse designed PWR. The COSI tests demonstrated that the current NOTRUMP condensation model under-predicted condensation in the intact loops during Si and, thus, is a conservative model. Use of the improved condensation model has demonstrated that the current NOTRUMP SBLOCA analyses without the improved condensation model and no Si into the broken loop are more conservative (higher calculated PCT) than a case that includes Sl into the broken loop and the improved condensation model. A minimum benefit of -150*F has been assigned for the improved l
condensation.
-an l
l
Discussion of Small Break LOCA Mode! Errors /Model Changes Page 2 3.
Drift Flux Flow Regime Errors (-13 F)
Errors were discovered in both WCAP-10079-P-A and related coding in NOTRUMP SUBROUTINE DFCORRS where the improved TRAC-P1 vertical flow regime map is evaluated. In evaluation model applications, this modelis only used during counter-current flow conditions in vertical flow links. The affected equation in WCAP-10079-P-A is Equation G-65 that previously allowed for unbounded values of the parameter C,
contrary to the intent of the original source of this equation. This allowed a discontinuity to exist in the flow regime map under some circumstances. This was corrected by placing an upper limit of 1.3926 on the parameter C.,as reasoned from the discussion in the original source. As stated, this correction retumed NOTRUMP to consistency with the original source for the affected equation.
Further investigation of the DFCORRS uncovered an additional closely related logic error that led to discontinuities under certain other circumstances. This error was also corrected and retumed the coding consistency with WCAP-10079-P-A.
Representative plant calculations indicated PCT effects ranging from -13 F to -55 F. For the purpose of tracking PCT, the minimum benefit of-13*F has been assigned to these changes for Farley. However, it has bean demonstrated that the effect of these changes n,ay exceed 50 F and, therefore, is being reported under 10CFR50.46.