W3P86-2941, Forwards Response to Request for Addl Info Re Methodology Used to Perform Large Break LOCA Analyses for Cycle 2 Reported in Part B of Reload Analysis Rept

Forwards Response to Request for Addl Info Re Methodology Used to Perform Large Break LOCA Analyses for Cycle 2 Reported in Part B of Reload Analysis Rept

ML20214P044
Person / Time
Site:	Waterford
Issue date:	11/26/1986
From:	Cook K LOUISIANA POWER & LIGHT CO.
To:	Knighton G Office of Nuclear Reactor Regulation
References
W3P86-2941, NUDOCS 8612040060
Download: ML20214P044 (4)

Text

- - - - _ _ . _

l oa

'q I OUISI&ANA POWER LIGHT/ 317NEW BARONNESTREET + P. O. BOX 60340 ORLEANS, LOUISIANA 70160 =

(504)595-3100 UTTONEOYIU November 26, 1986 W3P86-2941 A4.05 OA Mr. George W. Knighton, Director PWR Project Directorate No. 7 Division of PWR Licensing-B Office of Nuclear Reactor Regulation Washington, D.C. 20555

SUBJECT:

Waterford SES Unit 3 Docket No. 50-382 Response to Request for Additional Information on Waterford 3 Cycle 2 Reload Analysis Report

Dear Mr. Knighton:

By the referenced letter LP&L submitted Part B of the Waterford 3 Cycle 2 Reload Analysis Report (RAR). This submittal included those sections of the RAR that described both the LOCA and non-LOCA safety analyses.

In subsequent discussions with your staf f, additional information was requested regarding the methodology used to perform the large break LOCA analysis for Cycle

2. Enclosed please find the LP&L response.

Should you require further information, please contact Mike Meisner at (504) 595-2832.

Yours very truly, b bb K.W. Cook Nuclear Safety and Regulatory Affairs Manager KWC/MJM/p1m cc: B.W. Churchill, W.M. Stevenson, R.D. Martin, J.H. Wilson, N. Lauben (NRC/NRR),

NRC Resident Inspector's Office (W3)

Enclosure 8612040060 861126 2 DR ADOCK 0500 I

"AN EQUAL OPPORTUNITY EMPLOYER"

i

%e QUESTION:

Justify why the change in axial power shape and the no single failure assumption (maximum LPSI flow) used in Cycle 2 do not shift the size ,

of the limiting break.

RESPONSE

The results of the large break LOCA calculation of record for Cycle 1 were submitted to NRC in Reference 1. This calculation was done for

'the worst break size determined from previous spectrum studies and included the NUREG-0630 model change and a revised axial power shape to address the axial shape sensitivity issue. The NRC approved the analysis and this approval was documented in Reference 2. The Cycle 2 analysis used the same methodology as the approved Cycle 1 analysis except for the maximum low pressure safety . injection (LPSI) flow assumption and a small change to the axial power shape to remove excess conservatism in the Cycle 1 shape. Figure 1.shows the Cycle 1 and Cycle 2 axial power shapes. This evaluation justifies that the-change in axial power shape and maximum LPSI flow assumption have no significant impact on the sensitivity of large break LOCA results to break size and therefore, that the worst break for Cycle 1 is also the worst break for Cycle 2.

The sensitivity of large break LOCA results to break size is determined by the blowdown hydraulics and the small-variation between break sizes in hot rod fuel temperatures at end-of-blowdown (E0B). This relative temperature variation at E0B is propagated through the reflood period and results in the same relative variation in peak clad temperature (PCT) between the large break LOCA's. The change in axial power shape and maximum LPSI flow assumption used for Waterford 3 Cycle 2 have no significant impact on the blowdown (or reflood)' hydraulics that would cause a change in the worst break size.

The Cycle 1 blowdown hydraulics calculation is applicable to Cycle 2 because there are no significant input changes for Cycle 2. The effect of axial power shape on the blowdown hydraulics is not signif-icant. The blowdown is so rapid for large breaks that differences in the axial power distribution have little effect on the fluid conditions which determine the blowdown hydraulic response. Calculations done on other CE plants solely to address the effect of the new axial power shape (consistent with the methodology approved in Reference 3) on the blowdown hydraulics have shown that the hot spot average fuel temperature at E0B decreases by less than 4*F. Since this result occurred for different types of CE plants, the same insignificant effect can be expected to occur for the large breaks on Waterford 3. In addition, the change in axial power shape for Waterford 3 between the currently approved Cycle 1 analysis and the Cycle 2 analysis is smaller than the change in axial shape for these calculations. Thus, the break size

4 RESPONSE: (cont'd) with the highest fuel temperature at E0B for Cycle 1 would also have the highest fuel temperature at E0B for Cycle 2 with the new axial shape. The maximum LPSI flow assumption has no impact at all on blowdown since the LPSI pumps do not inject any water during blowdown.

The variation between break sizes in E0B fuel temperature is propagated through the reflood period and results in the same relative variation in PCT. For all large breaks, the reactor vessel downcomer remains completely full throughout reflood with or without the maximum LPSI flow assumption. Thus, this assumption only results in a slightly greater spillage of water into containment and a small decrease in containment pressure. The reduced pressure equally affects all break sizes. In fact, since the reflood behavior is the same, all large breaks utilize identical FLECHT heat transfer coefficients during reflood. Thus, no changes between break sizes occur due to reflood and the same relative variation between breaks that exists at E0B will also exist for the PCT. Furthermore, since the PCT for Waterford 3 occurs at a FLECHT cooled location (below cladding' rupture), small differences in the timing of cladding rupture or steam cooling heat transfer coefficients between breaks have no effect on the PCT.

Therefore, since the axial power shape and maximum LPSI flow assumption have no significant impact on the sensitivity of the large break LOCA results to break size, the worst break size from Cycle 1 is also the worst break size for Cycle 2.

Reference 1: LP&L Letter W3P85-2177, dated July 19, 1985 Reference 2: Letter from J. H. Wilson (NRC) to G. W. Muench (LP&L)

"Large Break LOCA Reanalysis for Waterford 3',' May 6,1986

' Reference 3: Letter from D. M. Crutchfield (NRC) to A. E. Scherer (CE),

. - " Safety Evaluation of CE ECCS Large Break Evaluation Model

and Acceptance for Referencing of Related Licensing Topical j

Reports", July 31, 1986 i

i

4 3

~

FIGURE 1 Wa:er orc Cyc e anc 2 Axial Power Shape Comparison 17 -

16 -

15 -

14 -

2 13 -

\

j 12 -

11 -

e o 10 -

e t 9-l0 8-1 7-o 6-o

.E 5-J 4-3-

2-1-

0 i , i i i , , , ,

0 20 40 60 80 100 Axici Position (%)

Cycle 1 + Cycle 2 n - t