ML12355A161

PG&E Handouts from the December 18, 2012, Meeting with the NRC Related to Emergency Core Cooling System Evaluations (TAC Nos. MF0313 and MF0315)

ML12355A161
Person / Time
Site:	Diablo Canyon
Issue date:	12/18/2012
From:	Andrachek J, Fink D, Gresham J, Schrader K, Sharp M, Summy J Pacific Gas & Electric Co, Westinghouse
To:	Plant Licensing Branch IV
Sebrosky J
References
TAC MF0313, TAC MF0315
Download: ML12355A161 (19)

Text

Diablo Canyon Power Plant Use of Leak-before-break for Fuel Structural Analyses Jeff Summy Ken Schrader Mark Sharp Pacific Gas & Electric Co.

Jim Gresham Dave Fink Jim Andrachek Westinghouse December 18, 2012 1

Objectives Describe the Licensing Basis Verification Project Describe the Issue in the Corrective Action Program Describe the Emergency Core Cooling System (ECCS) analyses l performed f d to satisfy i f 10CFR50 10CFR50.46(b)(1),

46(b)(1) (b)(2)

(b)(2),

(b)(3), (b)(4), and (b)(5)

Describe the fuel assembly seismic and LOCA structural analysis and the interface with 10CFR50.46 (b)(4)

Actions going forward Questions and Feedback 2

Licensing Basis Verification Program PG&E is performing a Licensing Basis Verification Project (LBVP) for Diablo Canyon The LBPV is a comprehensive program to verify the Diablo Canyon licensing basis and to identify and correct deficiencies and inaccuracies The goal of the LBVP is to develop a clear and accurate licensing basis for Diablo Canyon 3

Description of Non-Conforming Non Conforming Condition PG&E identified a potential deficiency in the way that the use of leak-before-break leak before break (LBB) methodology was incorporated into licensing basis Specifically, PG&E did not perform a 10 CFR 50.59 review for a change where LBB methodology was implemented to exclude the dynamic effects of a break in the main loop piping in the fuel assembly structural analyses performed to address Appendix A of SRP Section 4.2, 4 2 Fuel Fuel System Design Design The results of the fuel assembly structural analyses are used in part to demonstrate compliance with the 10 CFR 50.46(b)(4) fuel coolable l bl geometryt requirements i t On September 25, 2012, PG&E documented the deficiency as a non-conforming condition in the Diablo Canyon corrective action program 4

Description of Non-Conforming Non Conforming Condition An operability determination was performed and the fuel and ECCS was determined to be operable based on the current analysis (WCAP-16946) conclusions being valid and previous NRC approval in licensing actions at two other plants PG&E has identified a significant amount of information on the existing Diablo Canyon licensing basis and how other plants have adopted use of LBB methodology in the fuel assembly structural analyses A summary of the information is provided in this presentation for discussion 5

LOCA analyses performed to satisfy 10CFR50.46 10CFR50 46 The NRC approved Diablo Canyon large break LOCA Emergency Core Cooling System (ECCS) analysis for each unit is based on NRC approved Westinghouse best-estimate LOCA (BELOCA) evaluation models:

- Unit 1: WCAP-12945-P-A, Addendum 1-A

- Unit 2: WCAP-16009-P-A (ASTRUM)

A double-ended d bl d d guillotine ill ti llarge b breakk LOCA iin th the main i lloop piping is considered in the ECCS analysis.

6

LOCA analyses performed to satisfy 10CFR50.46 10CFR50 46 In the BELOCA ECCS evaluation models, no credit is taken for LBB to eliminate primary coolant main loop piping breaks when demonstrating that the acceptance criteria of 10CFR50.46 are met:

• (b)(1) - Peak Cladding Temperature

• (b)(2) - Maximum Cladding Oxidation

• (b)(3) - Maximum Hydrogen Generation

• ((b)(4)

)( ) - Coolable Geometryy

• (b)(5) - Long Term Cooling 7

LOCA analyses performed to satisfy 10CFR50.46(b)(4) 10CFR50 46(b)(4)

Coolable ggeometryy is considered in the BELOCA ECCS analyses by modeling the effects of individual rod or hot assembly fuel rod burst and blockage, and is satisfied by demonstrating compliance with 10CFR50 10CFR50.4646 b(1) and b(2)

The BELOCA ECCS evaluation models, include additional evaluations to confirm coolable geometry, beyond rod

/ g , in the ECCS analysis burst/blockage, y when fuel assemblyy grid deformation is determined to occur WCAP-12945-P-A, Volume 5 Rev 1 describes method Method depends on location of assemblies with grid deformation, independent of break size 8

LOCA analyses performed to satisfy 10CFR50.46(b)(4) 10CFR50 46(b)(4)

BELOCA ECCS ggrid deformation model Fuel assembly periphery grid deformation: No peak cladding temperature penalty assessed Fuel assembly in in-board board (interior) grid deformation:

Additional evaluations performed as defined in WCAP-12945-P-A, Volume 5 Rev 1 9

LOCA analyses performed to satisfy 10CFR50.46(b)(4) 10CFR50 46(b)(4)

The fuel assembly seismic and LOCA structural analysis determine if fuel grid deformation occurs due to the impact forces exceeding the minimum grid test strength The DCPP BELOCA analyses do not need to address the effect of grid deformation, since in-board (interior) grid deformation is not calculated to occur in the fuel assembly structural analyses Consistent with the WCAP-12945-P-A, Volume 5, Revision 1 methodology 10

Fuel assembly seismic and LOCA structural analysis Th The currentt DiDiablo bl C Canyon ffuell assembly bl seismic i i and d LOCA structural analysis is documented in WCAP-16946 that supported reactor head replacement l t The analysis is performed in accordance with Appendix A to SRP Section 4.2, Fuel Fuel System Design Design input for the fuel assembly response should include motions of the core plate, core shroud , fuel alignment plate, or other relevant structures (these motions should correspond to the break that produced the peak fuel assembly loadings in the primary coolant system and reactor internals analysis) 11

Fuel assembly seismic and LOCA structural analysis Th The methodology th d l ffor th the ffuell structural t t l analyses l iis based on the NRC approved method contained in WCAP-9401-P-A, Verification and Testing Analysis of th 17 the 17x17 17 OOptimized ti i d FFuell A Assembly, bl d dated t dAAugustt 1981 SRSS combination of LOCA and seismic loads Referenced in the Diablo Canyon LAR and associated Amendments 37/36 for the use of Vantage 5 Optimized Fuel 12

Fuel assembly seismic and LOCA structural analysis Th The ffuell structural t t l analysis l i contained t i d iin WCAP-9401-P-A, Verification and Testing Analysis of the 17x17 Optimized Fuel Assembly, used a main loop piping i i b breakk off ~ 1ft2 Based on a reactor vessel inlet nozzle break being structurally limited to less than 1ft2 The same break size was assumed in a report for Diablo Canyon, Response to Combinations of Calculated Loads For Pipe Break and Earthquake, Earthquake, submitted to the NRC on February 2, 1978 and referenced in Supplement 8 to the Safety Evaluation Report dated November 15, 1978 13

Fuel assembly seismic and LOCA structural analysis Th The NRC approved d th the LBB analysisl i (WCAP (WCAP-13039) 13039) for f

the Diablo Canyon main loop piping in a Safety Evaluation dated March 2, 1993 SStaff ff conclusion:

l i Th staff The ff concludes l d that h theh lilicensee's

' LBB analysis is consistent with the criteria in NUREG-1061, Volume 3, and draft SRP 3.6.3.; therefore, the analysis complies with GDC GDC-4.

4. Thus, the probability of large pipe breaks occurring in the RCS line is sufficiently low that the dynamic effects associated with postulated pipe breaks need not be a design basis 14

Fuel assembly seismic and LOCA structural analysis Th The pipe i rupture t lloads d usedd iin th the ffuell assembly bl structural analyses (WCAP-16946), are based on the most limiting of an accumulator, pressurizer surge line, andd RHR branch b h liline b breaks k

Limitation of breaks to branch line breaks (exclusion of main loop breaks) is based on application of the LBB methodology in accordance with the 1987 revision to GDC-4 Allows exclusion of dynamic effects from the design basis analyses when LBB analyses are approved by the Commission 15

Fuel assembly seismic and LOCA structural analysis The NRC Leak-Before-Break Knowledge Management Document (p (page g 3)) pprovides additional information on the dynamic effects that can be excluded when LBB is approved

• Only local dynamic effects

• Discharging fluids The NRC Leak-Before-Break Knowledge Management Document (page

( 3)) provides permitted plant l activities

• Decompression waves within the intact portion of the piping system 16

Fuel assembly seismic and LOCA structural analysis WCAP-16498-NP, 17x17 Next Generation Fuel (17x17 NGF), dated March 2008, has stated fuel qualification NGF),

analyses are performed postulating the rupture of branch lines connected to the main coolant loop (page 61):

Currently, all Westinghouse designed US PWR primary coolant main loop piping has been excluded from consideration for dynamic effects associated with postulated pipe rupture under Reference 61 or subsequent LBB analyses. As a result, all current fuel qualification analyses are performed on the basis of postulated rupture of branch lines connected to the primary i coolant l t lloop.

WCAP-16498-NP was approved in an NRC Safety Evaluation dated March 16,, 2011 17

Fuel assembly seismic and LOCA structural analysis The Staff recently approved the use of LBB for fuel assembly seismic and LOCA structural analyses as part of the Turkey Point Units 3 and 4 Extended Power Uprate Licensing Amendment Request in a letter dated June 15, 2012 (ML11293A356)

Section 2.8.1 of the NRC Safety Evaluation reflected use of WCA-9401-P-A methodology and use of largest branch line breaks The licensee evaluated seismic and LOCA loading using the approved methodology described in WCAP-9401-P-A The largest branch line breaks, either the accumulator line (ACC) break, surge line break, or RHR line break, were considered when generating LOCA hydraulic forcing functions used as input to the analysis 18

Resolution of Issue PG&E is prepared to take the actions necessary to resolve the non-conformingg condition and improve p the licensing basis PG&E is determining what conservative approach is required i d to address dd the h non-conforming f i condition di i and d close the operability determination PG&E plans to work collaboratively with the Staff to understand and resolve the issue 19