ML20199A206

Summary of 971106 Meeting W/Wog in Rockville,Md Re Issues Related to 10CFR50.46.List of Participants & Presentation Matl Encl

ML20199A206
Person / Time
Issue date:	01/15/1998
From:	Craig C NRC (Affiliation Not Assigned)
To:	Essig T NRC (Affiliation Not Assigned)
References
PROJECT-694 NUDOCS 9801270149
Download: ML20199A206 (97)

Text

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, NUCLEAR REGULATORY COMMISSION 2 WASHINGTON D.C. 30646-0001 6

9 * * * * * ,o January 15, 1998 MEMORANDUM FOR: Thomas H. Essig, Acting Chief Generic lasues and Environmental Projects Branch Division of Reactor Program Management Office of Nuclear Reactor Regulation

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FROM: Claudia M. Craig, Senior Project Manager .Qd. O,., bi O Geneiic lasues and Environmenta! Projects Branch Division of Reactor Program Management Office of Nuclear Reactor Regulation

SUMMARY

OF MEETING WITH THE WESTINGHOUSE OWNERS GROUP (WOG) TO DISCUSS ISSUES RELATED TO 10 CFR 50.46 The subject meeting was held at the NRC offices in Rockville, Maryland on November 6,1997, between representatives of the WOG, Westinghouse, and the NRC staff. In a letter dated October 28,1997, Westinghouse informed the NRC staff that it had discovered a non-t conservatism in toe oxidation model for high bumup Zircalloy-4 clad Integral Fuel Burnable Absorber (IFBA) fuel. The model was non-conservative when compared to data for IFBA fuel with greater than about 39-40K MD/MTU bumup. !nformation provided by Westinghouso stated j that this was t.ot a safety issue, but there was a question of compliance with 10 CFR 50.46(b)(2) (greater than 17% local c.ladding oxidation). Based on this information, the staff, Westinghout.e, and the WOG agreed to meet to further discuss the issue. Attachment 1 is a list of meeting participants. Attachment 2 is a copy of the presentatic, material discussed at the meeting.

At the meeting, Westinghouse discussed the fuel corrosion model and code used to calculate initial fuel conditions for LOCA analyses. Westinghouse had been working on the ne".* 'uf.I corrosion model and pursuing incorporation of the new modelinto the code when it discovered the non-conservatism.

To address the safety determination and compliance issue, Westinghouse described the generic rod performance analysis it performed to demonstrate the adequacy of screening criteria to be applied to plants using Westinghouse fuel. Westinghouse stated the results of the analysis, assuming gap re-opening, indicate that all aspects of plant safety analyses remain bounding except for the potential to exceed the no gap re-opening design criteria. Although 10 CFR 50.46 does not contain gap reopening criteria, with this potential for gap re-opening, 98-/G the possibility to exceed the 17% LOCA oxidation limits prescribed in 10 CFR 50.46 exists.

Westinghouse also performed a generic LOCA assessment of the gap re-opening scenario and concluded the 10 CFR 50.46 criteria would be satisfied for small break LOCAs, and the PCT criteria would continue to be met. Westinghouse discussed some experiments performed by the French that identified failures at certain oxidation levels which were above the 17%

prescribed in 10 CFR 50.46. Westinghouse performed additional parametric studies to [

calculate the oxidation due to LOCA for the gap re-opening scenario. Westinghouse presented ,

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T. Essig; -2 January 15. 1998 information to' support why Westinghouse does not believe that greater than 5%_ additional oxidation would take place during a LOCA or other event. The results of these studies

_ indicated low safety significance, the LOCA assessment is conservative, and provided a +

reasonable method for assessing LOCA oxidation. ,

Screening criteria were developed to address compliance with 10 CFR 50.46. Plants and fuel act affected by this issue include:- fuel in the first half of the operating cycle or retuming from an

~

outage, fuel in the third cycle, and plants without IFBA fuel This issue does not apply to ZlRLO '

fuel, but no plant has all ZlRLO fuel at this time. Plants potentially affected by this issue include plants with the following: IFBA fuel with Zircalloy 4 cladding in the second half of the second cycle may have gap re-opening; those plants that may have gap re-opening and pre-accident clad oxidation greater than 12%. The WOG identified one plant that exceeded the screening

, criteria, but no further analysis was performed because the plant was in the process of shutting down fo.' a scheduled refueling outage.

The WOG identified a list of affected plants and indicated that as each plant exceeds the screening criteria (in about four to six weeks) Westinghouse will perform a detailed analysis to

' determine compliance with 10 CFR 50.46, and if 10 CFR G0.46 is not met, the plant would take appropriate actions per 10 CFR 50.46(a)(3)(li), including compensatory measures such as peal:ing limitations or dorating.' Subsequent to the meeting, it was clarified that these plant-specific assessment results and cor pensatory measures, if needed. would be provided to the  ;

. NRC. Westinghouse indicated it would continue to do more detailed assessments for plants, and make time ly assessments w!th regard to the compliance issue. In the longer term, Westinghouse discussed reviewing and improving the analvtical models by July 1998, gathering additional data to validate fuel performance methods through inspections by May 1998, and performing plant by plant assessments by July 1998.

The staff requested Westinghouse and the WOG provide the details that were discussed at the meeting in a letter submitted tu the NRC, including a discussions of the safety assessment, what plants will be affected next and when they will be affected, and more information on how l the ista developed over the months. Westinghouse submitten the information in letters dated L November 12,1997 and November 13,1997.

L The staff concluded that licensees using Westinghouse fuel are in present compliance with

10 CFR 50.46 requirements and that the overall plan orovided licensees a means to L demonstrate continued compliance with both the reporting and the analytical requirements of

-10 CFR 50.46.

~ Project No. ' 694 -

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,. s Attachments; As stated

- ccw/atts: See next page

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-2 January 15, 1998 l T. Essig information to support why Westinghouse does not believe that greater than 5% additional oxidation would take place during a LOCA or other event. The results of these studies indicated low safety significance, the LOCA assessment is conservative, and provided a reasonable method for assessing LOCA oxidation.

Screening criteria were developed to address comp,iance with 10 CFR 50.46. Plants and fuel not affected by this issue include: fuelin the first half of the operating cycle or returning from an outage, fuel in the third cycle, and plants without IFBA fuel. This issue does not apply to ZlRLO fuel, but no plant has all ZlRLO fuel at this time. Plants potentially affected by this issue include plants with the following: IFBA fuel with Zircalloy-4 cladding in the second half of the second cycle may have gap re-opening; those plants that may have gap re-opening and pre-accident clad oxidation greater than 12%. The WOG identified one plant that exceeded the screening criteria, but no further analysis was performed because the plant was in the process of shutting down for a scheduled refueling outage.

.The WOG identified a list of affected plants and indicated that as each plant exceeds the screening criteria (in about four to six weeks) Westinghouse will perform a detailed analysis to determine compliance with 10 CFR 50.46, and if 10 CFR 50.46 is not met, the plant would take appropriate actior., per 10 CFR 50.46(a)(3)(ii), including compensatory measures such as peaking limitations or derating. Subsequent to the meeting, it was clarified that these plant-specific assessment results and compensatory measures, if needed, would be provided to the NRC. Westinghouse indicated it would continue to do more detailed assessments for plants, and make timely assessments with regard to the compliance issue. In the longer term, Westinghouse discussed reviewing and improving the analytical models by July 1998, gathering additional data to validate fuel performance methods through inspections by May 1998, and performing plant by plant assessments by July 1998.

The staff requested Westinghouse and the WOG provide the details that were discussed at the meeting in a letter submitted to the NRC, including a discussions of the safety assessment, what plants will be affected next and when they will be affected, and more information on how the issue developed over the months. Westinghouse submitted the in'ormation in letters dated November 12,1997 and November 13,1997.

The staff concluded that licensees using Westinghouse fuel are in present compliance with 10 CFR 50.46 requirements and that the overall plan provided licensees a means to demonstrate continued compliance with both the reporting and the analytical requirements of 10 CFR 50.46 Project No. 694 Attachments: As stated ccw/atts: See next page DISTRIBUTION: See attached page DOCUMENT NAME: 11_6_97. MIN OFFICE PGEB SC:PGEB BC:SRXB ,

NAME CCraigfsh\ ,MMiIo 'TCollins 3 DATE I / [/98 / / If /98 //)g/98 OFFICIAL RECORD COPY

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WOG/NRC MEETING NOVEMBER 6,1997 MEETING PARTICIPANTS Name Oroanization Harold Scott NRC/RES l Shih-Liang Wu NRC/NRR/SRXB l Carl Beyer PNNL Joseph Staudenmeier NRC/NRR/SRXB Walton Jensen NRC/NRR/SRXB Tony Attard NRC/NRR/SRXD Edward Kendrick NRC/NRR/SF(B Lstry Phillips NRC/NRR/SRXB Scott Newberry NRC/NRR/DSSA Tlm Collins NRC/NRR/SRXB Eric Weiss NRC/NRR/SRXB Frank Orr NRC/NRR/SRXB Michael Baldwin NU REB David Lcunsbury PSE&G Allen Johnson NRR/DRPE/PD2-1 Ed Goodwin NRR/DRPM/PECB Kulin D. Desal NRC/NRR/SRXB J. David Campbell Westinghouse Hank Sepp Westinghouse NSD Barton Z, Cowan ESCM Nancy Chapman Bechtel for OPPD Tom Harding Rochester Gas & Electric Corp.

Bob White North Atlantic Energy Service Kenny Epperson Duke Power John Butler NEl Mitzl Young NRC/OGC Jose Garcia Florida Po,ser & Light Lynn Connor DSA-Gary Hollinger Florida Power & Light Vance VanderBurg AEP Terry Reis NRC/OE Harry Majors SNC John Galembush - Westinghouse Bob Calabro TVA George Uram - Westinghouse Giovanna Longo NRC/OGC David Colburn Westinghouse Attachment 1

MEETING PARTICIPANTS (Continued)

Susan Hoxie Key SNC Joe Scarfutti Westinghouse Sumit Ray Westinghouse Douglas Wise Commonwealth Edison Co.

Lucius R. Cartin SCE&G Vincent J. Esposito Westinghouse - CNFD -

Mitch Nissley Westinghouse - NSD Mark Fecteau Westinghouse - CNFD Elaina Hiruo inside NRC Stewart Bailey NRC/NRR/DRPW Christopher Jackson NRC/NRR/SRXB Lisa Campagna Westinghouse - Law Dept.

Claudia Craig NRC/NRR/PGEB Frank Akstulewicz NRC/NRR/PGEB l

l Attachment 1 l

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Fuel Performance Issues Presentation to NRC  :

l November 6,1997 Attachment 2 ,!

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i NRC/WOG/ Westinghouse Meeting 11/6/97 W Fuel Performance Models I. Meeting Objectives Tom Greene  ;

Chairman WOG  :

II. ' Issue Definition / Background W Mark Fecteau  :

III. Technical Summary W Mark Fecteau Status of Current Analyses Safety Assessment i

IV. Regulatory Compliance EVinny Esposito 1

V. Plan for Resolution E Vinny Esposito VI. WOG Involvement Tom Greene i

VII. Proprietary Discussions (as necessary)

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1 Meeting Objectives Provide an update on model development for PAD Provide safety and code significance Review Action Plan Provide for Future Communicatons

1 Issue Statement When the effects ofincreased corrosion are incorporated into current licensed version of PAD, gap re-opening may occur

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O Fuel Rod Rod Internal Pressure

- fission gas IFBA Coating

-IFBA Helium UO2 4 6- Gap Pellet Clad Performance

- RCS conditions

- Clad Material N

- Burnup History w f Cladding

- Corrosion (Oxidation)

- Internal pressure

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L Terminology IFBA-IntegralFuelBurnaale Absorber Zirc L - fael rod cladding material Gaa re-opening = clad liftoff I

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l Fuel Performance Model

Background

W fuel performance code is PAD PAD is licensec. methoc (WCAP-10851-P-A)

PAD is a collection of empirical models (UO2, gas release, c. ac. ding behavior, etc.)

PAD is usec. to demonstrate that licensec :~uel per:formance criteria are met for each reloac core a

PAD also provides reference fuel temperature inouts to transient analyses

...3 Fuel Performance Model

Background

In ear y 1996, Westinghouse discovered that the

roc internal pressure buildup due to Helium i release from IFBA was higher than previously modeled; 100% gas release assumed since In late 1996, Westinghouse completed development of a new corrosion model for Zirc-4 cladding material; this model was presented to the 3RC in December, '96

~

Fuel Performance Model Background .

Since early '97, Westinghouse has been pursuing ,

the incorporation of this new corrosion model into PAD and assessing feechack affects on other fuel performance criteria Higher corrosion is causing elevated cladding .

temperatures at end oflife (EOL) conditions, and

< consequently, higher outward creep rates and reduced pressure margin to the no gap re-openin3, limit

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Fuel Performance Model

Background

Conservatisms which compensate for the increased corrosion feedback effects are believed

. to exist in PAD:

- unirradiated creep rates are too conservative

- pellet-to-clad contact model too conservative j

- strain ~ reversal algorithm too conservative Additiona deve opment time is needed for W to quantify these conservatisms and implement PAD code improvements

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! Fuel Performance Model

Background

W's moc ified version of PAD currently incorporates: 1

- new Zirc-4 corrosion model '

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- ciscrepancy corrections, additional uncertainty i terms AL1 cores designed since early '97 have used the new corrosion model for checking steady-state oxidation accumulation Wi:hout other compensating modifications, this model j

.shows a significant decrease in gap re-opening i pressure margin

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Fuel Performance Model .

Limiting Duty Analysis Results i

For the most limiting duty cycle analyzed:-

- at 95% uncertainty, gap re-opening limit is exceeded for lead IFBA rod about half-way into its 2nd cycle of burnup .

- using the model without uncertainties, gap re-  !

opening does not occur, even for the most limiting IFBA rods  !

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Fuel Performance Model Plant Implications Issue is limited to high duty fuel rods with IFBA and Gadolinia .

- non-IFBA rods do not build up sufficient internal t pressures to exceed system pressure

- low duty fuel rods do not buildup sufficient internal pressure or sufficient clad temperature heatup to exceed gap re-opening limit I

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O Safety Assessment k

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Gap Re-Opening Scenario Fuel Reliability t

- No roc failure 1

- believed to be the most probable outcome r

- higher temperatures & pressures within high burnup fuel rods . 1 Rapid rod failure  :

- believed to be a highly improbable (statistical) outcome  ;

- have never seen this failure mechanism in fuel exams -

4 i

- individual rod failure, should it occur, would be immediately detectable in coolant activity level

> Westinghouse believes that gap re-opening will not lead to fuel rod failure .

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Gap Re-Opening Scenario j Bounding Rod Performance Analysis i

Bounding fuel rocL performance scenario analyzed as a' pre-condition to design basis events j Simulated bounding duty rod using conservative assumptions (to bound all plants and consider key uncertainties)

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- cladding oxidation at upper limit l;

- upper bound fission gas release

- lower bound oxide thermal conductivity

- degraded CO2 thermal conductivity

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Gap Re-Opening Scenario Bounding Rod Performance Analysis Gap re-opening localized to a few inch segment at point of worst corrosion auildup (about 10 feet up)

Slow increase in pellet-clad gap with continued operation Slow heatup of pellets in that area cue to gap's addidonal thermal resistance Additienal gas release from these pellets due to hotter temperatures

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Gap Re-Opening Scenario .

. Bounding Rod Performance Analysis Bounding duty rod simulation showed:

- small gap re-opening (less than initial BOL gap)

- increased rod internal pressure

- increased local pellet temperature l Monte-Carlo simulation of probable 95%

uncertainty combinations shows that safety ana.ysis reference case is conservative

Temperature increase offset somewhat by natural-power burndown of high burnup fuel rods i

1 -

L Safety Evaluation l Assuming Gap Re-opening Pre-condition of hotter rods anc higher internal pressures were consic ered in each design basis transient event (Condition I, II, III, and IV)

All transients occur too rapidly to see any change in gap re-opening via creep out No new accident scenarios are created by the gap re-opened condition

s. s. * .

Safety Evaluation Assuming Gap Re-opening All aspects of plant safety analyses remain bounding (LOCA, Xon-LOCA, T/H, Core Design, Fuel Rod. Design}, except for:

- potential to exceed no gap re-opening design limit

- wit:1 potential gap re-opening, possibility to also exceed 17% LOCA metal wastage criteria Gap re-opening does not necessarily imply that 17% LOCA limit will be exceeded i

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Safety Evaluation Gap Re-opening Summary N

Gap re-opening does not lead to fuel failures Gap re-opening does cause elevated temperatures and pressures in high duty rods j

! Gap re-opening does not cause previously analyzed ~ design basis accident scenarios to become worse i

-Gap re-opening is oflow safety significance

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Safety Evaluation 17% Local Oxidation Criterion - Background l

- 10CFR50.46 Acceptance Criteria for PCT and local oxidation, in combination, established to limit embrittlement and potential for fuel fragmentation during quench Fragmentation tied to coolable geometry requirement

- Tests used to define limits were not representative of high burnup fuel ~

- pre-transient oxidation

- irradiation effects

- W has interpreted 10CFR50.46 limit on maximum loca!

oxidation as applying to pre-transient plus transient oxidation

Safety Evaluation Recent French Experiments Performed with Irradiated & Corroded Data Reported at 1996 Water Reactor Safety Meeting (NUREG/CP-0157, Vol.1, pp 161-172)

- Cladding samples taken from 5-cycle fuel with average rod burnup of 60 GWD/MTU

- 30 tests performed,25 retained / reported

~80% from mid-core elevations (oxide thicknea 50-70 microns, equivalent to 6-8% initial cladding oxidation)

~20% from limiting (high) elevations (oxide thickness60-120 microns, equivalent to 7-14%)

- Single and double-sided oxidation experiments perfdrmed

Safety Evaluation Recent French Experiments Performed with 4

Irradiated & Corroded Data Assessment of" failed" samples performed conservatively

- few samples visibly cracked or fragmented ,

- internal overpressure applied while sample immersed in

water, observation of gas bubbling considered to be failed j cladding I -

No failures observed with <17% transient oxidation (in addition I to pre-transient oxidation) 4 Failure limits of 23% total oxidation (pre-transient + transient) observed for single-sided oxidation,33% for two-sided

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Safety Evaluation LOCA Assessment of Gap Re-opening Scenario Generic in nature, no plant-specific calculations performed Used existing sensitivity studies to estimate effects on PCT and local oxidation Conicusions:

- 10CFR50.46 criteria satisfied for small break LOCA

- ~

- Local oxidation criterion may be exceeded by a small amount for large break LOCA, primarily due to pre-transient oxidation. PCT criterion would continue to be met .

- French data support the conclusion that the safety significance is low .

1 Safety Evaluation Additional LOCA Efforts to Date Goal: calculate incremental oxidation due to LOCA, for gap re-opening scenario ,

Limited scope parametric studies performed using approved best-estimate large break LOCA codes '

WCOBRA/ TRAC - predicts system thermal-hydraulic .

response, provides fluid conditions for detailed assessment of limiting location in the core

- HOTSPOT - analyzes limiting location in the core a

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Safety Evaluation '

Additional LOCA Efforts to Date WCOBRA/ TRAC parametric studies

- Selected top-skewed power shape with peak at elevation of interest .

- Scaled power distribution to reflect reduction in achievable power .

- Increased fuel temperatures to account for fuel thermal .

conductivity degradation with burnup  ;

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Safety Evaluation Additional LOCA Efforts to Date .

HOTSPOT parametric studies modeled maximum pre-transient oxide thickness (restricts allowable transient oxide to 2% of oxide thickness) varied initial fuel temperature (fuel thermal conductivity multiplier added as an option)  ;

varied local KW/Ft

" time scale stretching" applied

Safety Evaluation Gap Re-opening Study - LOCA Results for 15x15 Fuel 1 l

LDCA C1JSE ATMEL IUr BDBUPSI? %OXIITN l RIH REN (BOL) 0 1976 NO

20%BURNDOWN -230 1649 YES 0.9  ;

I

. 20%BURNDOWN,+200F -20 1816 YES 1.7 DECREASEDIGUEL +180 1871 YES 23 1 -1.2KWFr -180 1695 YES 1.1 30%BURNDOWN,+200F -180 1617 YES 0.7 l

l . '. .

Safety Evaluation

Gap Re-opening Study - LOCA Results for 17x17 Fuel LOCA CASE TFUEL PCT BD BURST?  % OXID'N i

REFERENCE A (BOL) 0 1936 NO 20% BURNDOWN -220 1549 YES 0.9 20% BURNDOWN,+200F -20 1627 YES 1.7 DECREASED KFUEL +770 1862 YES 2.8

-1.0 KW/FT 1600 YES 1.3 REFERENCE B (BOL) 0 2114 NO 20% BURNDOWN,+200F 0 1661 YES 1.9

+ 0.4 KW/FT, AKFUEL +150 1749 YES 2.7 t - ~ -

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Safety Evaluation

, LOCA Conclusions LOCA assessment confirmed to be conservative Adc.ec confic.ence t aat safety significance is low Reasona ale metaod for assessing incremental LOCA oxic ation for gap re-opening scenario has been

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Regulatory Compliance 1

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i Screening Criteria to Address

! Compliance 1 Plants in the 1st half of their operating cycle or returning i from an outage are all in compliance l 2 Plants in the latter half of their operating cycle may have gap re-opening 3 All plants predicted to have gap reopening, but which have

. pre-oxidation < ~12% (based on latest corrosion model) are in compliance Based on current information, which needs to be verified, all plants except one pass the screening criteria today. The exception would likely show acceptable results, but ramping down today to enter normal refueling outage -

i

Screening Criteria to Address Compliance In approximately 1 month, a limited number of plants may exceed the oxidation screening criteria.

T1ese plants will ae assessed prior to predicted ,

c ate of exceec ing the screening criteria T1is assessment will be performed based on the described sensitivity methodology with plant

specific conditions -

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t Long-Term Plan for Resolution l

Step 1 Review & Improve Analytic Models

- Assigned full-time team of dedicated indivicnals to review fuel performance methocology and models (on-going)

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- 1/98: complete top-to-bottom review of  :

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methoc s and models

- 3/98: develop program plan i .

- 4/98: meet with NRC to review program plan

- 7/98: modify PAD code and methods l

=

! Long-Term Plan for Resolution Step 2

! i j Gather Additional Data to Validate Fuel

! Performance Methods l

l - 11/97: identify what additional data collection i

would be beneficial and develop plan for

collection -

- 12/97 to 5/98

complete on-site inspections i

i l

a Long-Term Plan for Resolution Step 3 Plant-by-Plant Assessments

- 12/97: design new fuel assemblies to ensure ac equate rod internal pressure margin exists for each plant's intended duty scenario

- 7/98: begin formal plant-by-plant assessments l to show that limits are met wita modified PAD code using plant-specific margins l

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.e WOG Involvement ,

4 Current Dialog Licensee Event Report ,

Future Interactons I

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Westinghouse Owners Group l i

cc: ,

Mr. Nicholas Liparulo Westinghouse Electric Corporation  ;

Mail Stop ECE 415 P.O. Box 355  :

Pmsburgh, Pennsylvania 15320-0355 j Mr. Hank Sepp Westinghouse Electric Corporation i Mail Stop ECE 4 07A P.O. Box 355

. Pittsburgh, Pennsylvania 15320-0355

- Mr. Andrew Drake Westinghouse Owners Group Westinghouse Electric Corporation  :

Mail Stop ECE 516 ,

P.O. Box 355 Pittsburgh, Pennsylvania 15320 4 355

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t CISTRIBUTIQhi w/ attachments: Summary of Noverber 6,19g7, meeting with WOG dated -!

ilanuary 15. .998 -

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,- Centra Files PlJBLIC Project File  !

PGEB R/F

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• • • • • January 15, 1998 MEMORANDUM FOR: Thomas H. Essig, Acting Chief Generic issues and Environmental Projects Branch Division of Reactor Program Management Office of Nuclear Reactor Regulation FROM* Claudia M. Craig, Senior Project Manage Njds [.

Generic issues and Environmental Projects Branch Division of Reactor Program Management b Q('

Office of Nuclear Reactor Regulation

SUMMARY

OF MEETING WITH THE WESTINGHOUSE OWNERS GROUP (WOG) TO DISCUSS ISSUES RELATED TO 10 CFR 50.46 The subject meeting was held at the NRC offices in Rockville, Maryland on November 6,1997, between representatives of the WOG, Westinghouse, and the NRC staff, in a letter dated October 28,1997, Westinghouse informed the NRC staff that it had discovered a non-conservatism in the oxidation model for high burnup Zircalloy-4 clad Integral Fuel Bumable Absorber (IFDA) fuel. The model was non conservative when compared to data for IFBA fuel with greater than about 39-40K MD/MTU bumup. Information provided by Westinghouse stated that this was not a safety issue, but there was a question of compliance with 10 CFR 50.46(b)(2) (greater than 17% local cladding oxidation). Based on this information, the staff, Westinghouse, and the WOG agreed to meet to further discuss the issue. Attachment 1 is a list of meeting participants. Attachment 2 is a copy of the presentation material discussed at the meeting.

l At the meeting, Westinghouse discussed the fuel corrosion model and code used to calculate initial fuel conditions for LOCA analyses. Westinghouse had been working on the new fuel corrosion model and pursuing incorporation of the new model into the code when it discovered the non conservatism.

To address the safety determination and compliance issue, Westinghouse described the generic rod performance analysis it performed to demonstrate the adequacy of screening criteria to be applied to plants using Westinghouse fuel. Westinghouse stated the results of the analysis, assuming gap re opening, indicate that all aspects of plant safety analyses remain bounding except for the potential to exceed the no gap re-opening design criteria. Although 10 CFR 50.46 does not contain gap reopening criteria, with this potential for gap re opening,

! the possibility to exceed the 17% LOCA oxidation limits prescribed in 10 CFR 50.46 exists, l Westingbouse also performed a generic LOCA assessment of the gao re-opening scenario and concluded the 10 CFR 50.46 criteria would be satisfied for small break LOCAs, and the PCT criteria wou d continue to be met. Westinghouse discussed some experiments performed by the French that identified failures at certain oxidation levels which were above the 17%

prescribed in 10 CFR 50.46. Westinghouse performed additional parametric studies to

calculate the oxidation due to LOCA for the gap re-opening scenario. Westinghouse presented

0 t

• January 15. 1998 j T. E ssig.. - 2 j Information to support why Westinghouse does not believe that greater than 5% additional  !

3 oxidetion would take place during a LOCA or other event. The results of these studes l indicated low safety significance, th) LOCA assessment is conservative, and provided a j reasonable method for assessing LOCA oxidation.

Screening ortleria were developed to address compliance with 10 CFR 60.46. Plants and fuel not affected by this issue include: fuel in the first half of the operating cycle or retuming from an outage, fuel in the third cycle, and plants without IFBA fuel. This issue does not apply to ZlRLO

! fuel, but no plant has all ZlRLO fuel at this time. Plants potentially affected by this issue include plants with the following: IFBA fuel with Zircelloy 4 cladding in the second half of the second ,

cycle may have gap re-opening; those plants that may have gap re opening and pre-accident clad oxidation greater than 12W The WOG identified one plant that exceeded the screening  !

- critoria, but no further analysis was performed because the plant was in the process of shutting i down for a scheduled refueling outage.  !

, i

~

The WOG identified a list of affected plants and indicated that as each plant exceeds the screening criteria (in about four to six weeks) Westinghouse will perform a detailed analysis to determine compliance with 10 CFR 60.46, and if 10 CFR 50.46 is not met, the plant would take .

appropriate actions per 10 CFR 50.46(a)(3)(ii), including compensatory measures such as  !

i peaking limitations r r dorating. Subsequent to the meeting, it was clarified that these plant-l- specific assessment results and compensatory measures, if needed, would be provided to the  ;

l NRC.- Westinghouse indicated it would continue to do more detailed assessments for plants, j and make timely assessments with regard to the compliance issue. In the longer term, i~

Westinghouse discussed reviewing and improving the analytical models by July 1998, gathering

- additional data to validate fuel performance methods through inspections by May 1998, and performing plant by plant assessments by July 1998.

The staff requested Westinghouse and the WOG provide the details that were discussed at the meeting in a letter submitted to the NRC, including a discussions of the safety assessment, what plants will be effected next and when they will be affected, and more information on how .

the issue developed over the months. Westinghouse submitted the information in letters dated -i November 12,19g7 and November 13,19g7.  !

- The staff concluded that licensees us!ng Westinghouse fuel are in present compliance with 10 CFR 50.46 requirements and that the overall plan provided licensees a means to  :

demonstrate continued compliance with both the reporting and the analytical requirements of 10 CFR 50.46,  ;

l i

Project No.1694  :

Attachments: As stated l cowlettsLSee next page i

'W--um e,su47"-Nse e u-eer V -1e- W- >Th8+ v- T +wT *e 4ygr + -+ ,tw any.wWD-W@e"*w 'dg- WW -

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' .e T. E ssig January 15. 1998 I. 2 b

<. information to suppori why Westinghouse does not believe that greater than 5% additional oxidation would take place during a LOCA or other event. The results of these studies 1- ind6cated low safety significance, the LOCA assessment is conservative, and provided a l 1 reasonable method for assessing LOCA oxidation I l

1 Screening criteria were developed to address compliance with 10 CFR 50.46. Plants er d fuel j j not affected by this issue include: fuel in the first half of the operating cycle or retuming from an j outage, fuel in the third cycle, and plants without IFBA fuel. This issue does not apply to ZlRLO 4 fuel, but no plant has all ZlRLO fuel at this time. Plants potentially affected by this issue include i plants with the following: IFRA fuel with Zircelloy 4 cladding in the second half of the second cycle may have gap re-opening; those plants that may have gap re-opening and pre socident  ;

j clad oxidation greater than 12% The WOG identified one plant that exceeded the screening i criteria, but no further analysis was performed because the plant was in the process of shutting j down for a scheduled refueling outage.

. The WOG identified a list of affected plants and indicated that as each plant exceeds the l screening criteria (in about four to six weeks) Westinghouse will perform a detailed analysis to j

- detennine compliance with 10 CFR 50.46, and if 10 CFR 50.46 is not met, the plant would take  !

appropriate actions par 10 CFR 50.46(a)(3)(ii), including compensatory measures such as i peaking limitations or dorating. Subsequent to the meeting, it was clarified that these plant- l specific assessment results and compensatory measures, if needed, would be provided to the NRC. Westinghouse indicated it would continue to do more detailed sesessments for plants, 2

and make timely assessments with regard to the compliance issue. In the longer term, j

. Westinghouse discussed reviewing and improving the analytical models by July 1998, gathering  ;

L additional data to validate fuel performance methods through inspections by May 1998, and performing plant by plant assessments by July 1998.  ;

The staff requested Westinghouse and the WOG provide the details that were discussed at the meeting in a letter submitted to the NRC, including a discussions of the safety assessment.

what plants will be affected next and when they will be affected, and m:>re information on how l the losee developed over the months. Westinghouse submitted the information in letters dated i l November 12,19g7 and November 13,1997.

1 ,

The staff concluded that lict'*es using West 6nghouse fuel are in present compliance with  :

, 10 CFR 50.46 requirements and that the overall plan provided licensees a means to demonstrate coni.nued compliance with both the reporting and the analytical requirements of i 10 CFR 50.46. ,

Project No. 694 l

_ Attachments: As stated -  ;

1 i U Lcow/atte: See next page. _

j DISTRIBUTION: See attached page DOCUMENT NAME: 11_6_97. MIN h' OFFICE PGES SC:PGEB . BC:SRXS , i NAME= CCrsigfeh _ , d icq 'TCollins 'l/M  ;

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DATE 4 / [ /98- 1 / l'f /98 / / g g /98 -

OFFICIAL RECORD COPYg o _. . . _ . m __ . . . _ _ . _ _ .. _. _ _ , . _ , _ _ _ .

. . . - - _. ~.

O O l l

CISTRIBUTIOh : w/ attachments: Summary of November 6,19g7. meeting with WOG dated l Canuary 15. 1998 i Hard Copy Central Filer,  :

I (PUGUC Project File PGEB R/F MMalloy CCraig j RCroteau E Mall:

SCollina'cMiraglia -

RZin .an 7 BFM JNe GHolahan/SNewberry TCollins EWeiss Forr LPhillips SLWu ,

MChatterton  !

EGoodwin EBenner SBailey HScott, RES JStaudenmeier WJensen AAttard EKendrick i AJohnson, PD21 KDesal MYoung, OGC {

TReis, OE

> GLongo, OGC CJackson FAkstulewicz  ;

i i 6

l WOG/NRC MEETING NOVEMBER 6,1997 MEETING PARTICIPANTS l Name Organization Harold Scott NRC/RES Shih Llang Wu NRC/NRR/SRXB Carl Beyer PNNL Joseph Staudenmeier NRC/NRR/SRXB Walton Jensen NRC/NRR/SRXB Tony Attard NRC/NRR/SRXB Edward Kendrick NRC/NRR/SRXB Larry Phillips NRC/NRR/SRXB Scott Newberry NRC/NRR/DSSA Tim Collins NRC/NRR/SRXB Eric Weiss NRC/NRR/SRXB Frank Orr NRC/NRR/SRXB Michael Baldwin NU REB David Lounsbury PSE&G Allen Johnson NRR/DRPE/PD21 Ed Goodwin NRR/DRPM/PECB Kulin D. Desal NRC/NRR/SRXB J. David Campbell Westinghouse Hank Sepp Westinghouse NSD Badon Z. Cowan ESCM Nancy Chapman Bechtel for OPPD Tom Harding Rochester Gas & Electric Corp.

Bob White North Atlantic Energy Service Kenny Epperson Duke Power John Butler NEl Mitzi Young NRC/OGC Jose Garcia Florida Power & Light Lynn Connor DSA Gary Hollinger Florida Power & Light Vance VanderBurg AEP Terry Reis NRC/OE Harry Majors SNC John Galembush Westinghouse Bob Calabro TVA

. George Uram Westinghouse

Giovanna Longo NRC/OGC David Colburn Westinghouse i

o Attachment 1 l

MEETING PARTICIPANTS (Continued)

Susan Hoxie Key SNC Joe Scarfutti Westinghouse Sumit Ray Westinghouse Douglas Wise Commonweshh Edison Co.

Lucius R, Cartin SCE&G Vincent J. Esposito Westinghouse CNFD Mitch Nissley Westinghouse - NSD Mark Fecteau Westinghouse CNFD Elaine Hiruo inside NRC Stewart Bailey NRC/NRR/DRPW Christopher Jackson NRC/NRR/SRXB Lisa Campagna Westinghouse Law Dept.

Claudia Craig NRC/NRR/PGEB Frank Akstulewicz NRC/NRR/PGEB Attachment 1 i

6 e r , n w -

4 Fuel Performance Issues l

I Presentation to NRC  ;

November 6,1997 i

Attachment 2

6 , ., q

. t NRC/WOG/ Westinghouse Meeting ,

11/6/97-W Fuel Performance Models i

I. Meeting Objr.ctives Tom Greene -

Chairman WOG i

1 II. Issue Definition / Background W Mark Fecteau  ;

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III. Technical Summary W Mark Fecteau Status ofCurrent Analyses Safety Assessnu:nt  :

i.

! IV. Regulatory Compliance W Vinny Esposito i

V. - Plan for Resolution W Vinny Esposito i VI. WOG Involvement Tom Greene  !

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VII. Proprietary Discussions (as necessary) t

. .e Meeting Objectives Provide an update on model c evelopment for PAD Provide safety anc code .

significance Review Action Plan Provide for Future Communicatons I

Issue Statement W:len the eifects ofincreasec corrosion are incorporated irr:0 curren: licensed version of PAD, gap re-opening may occur l

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Fuel Rod Rod Internal Pressure '

- fission gas IFBA Coating-

-IFBA Helium

[ UO2 * * -

P Pellet Clad Performance

- RCS conditions

- Clad Material

- Burnup History Cladding

- Corrosion (Oxidation)

- Internal pressure

l l Terminology IFBA-IntegralFuelBurnable Absorber Zirc fuel rod cladding material Gap re-opening = clad liftoff 6

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Fuel Performance Model

Background

W fuel performance code is PAD PAD is licensed method (WCAP-10851-P-A)  :

PAD is a collection of empirical models (UO2, i gas release, clac. ding behavior, etc.)

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PAD is bsed to demonstrate that licensed fuel  :

performance criteria are met for each reload core PAD also provides reference fuel temperature 4 inputs to transient analyses 1

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Fuel Performance Model  ;

Background

In ear _y 1996, Westinghouse discovered tnat the roc internal. pressure buildup due to Helium release from IFBA was higher than previously ,

. moc.e ec.; 100% gas release assumed since In late 1996, Westingnouse completed c.evelopment of a new corrosion model for Zirc-4 cladding material; this model was presented to the NRC inDecember, '96

~ ~ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

Fuel Performance Model

Background

[

Since early '97, Westinghouse has been pursuing tae incor30 ration of this new corrosion moc.el into PAD anc. assessing feedback affects on otaer :itel performance criteria Higaer corrosion is causing elevated clac.c ing temperatures at end oflife (EOL) conditions, and consec uently, higher outward creep rates and reduced pressure margin to the no gap re-opening limit

Fuel Performance Model

Background

Conservatisms which compensate for the increasec. corrosion feedback effects are be ieved to exist in PAD:

- unirradiated creep rates are too conservative

- pellet-to-clad contact model too conservative

- strain ~ reversal algorithm too conservative

. Additional development time is needed for W to quantify taese conservatisms and implement PAD coc.e improvements

Fuel Performance Model

Background

W's modified version of PAD currently incoraorates:

- new Zirc L corrosion moc el

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- discrepancy corrections, adc.itional uncertainty terms A: . cores c.esigned since early '97 have used the new corrosion model for checking steady-state oxidation accumu.ation '

Wiaout other compensating modi:ications, this model snows a significant c.ecrease in gap re-opening pressure margin

l Fuel Performance Model Limiting Duty Analysis Results For the most limiting duty cycle analyzed:-

l - at 95% uncertainty, gap re-opening limit is exceeded for lead IFBA rod about half-way into its .

2nd cycle of burnup

- using the model without uncertainties, gap re- i opening does not occur, even for the most limiting IFBA rods i i

L Fuel Performance Model Plant Implications Issue is limited to hign duty fuel rods with IFBA and Gadolinia

- non-IFBA rods do not build up sufficient internal pressures to exceed system pressure

- low duty fuel rods do not buildup sufficient internal pressure or sufficient clad temperature heatup to exceed gap re-opening limit

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...q Gap Re-Opening Scenario Fuel Reliability No rod failure

- believed to be the most probable outcome

- higher temperatures & pressures within high burnup fuel rods .

Raaic rod failure

- believed to be a highly improbable (statistical) outcome

- have never seen this failure mechanism in fuel exams

- individual rod failure, should it occur, would be immediately detectable in coolant activity level

> Westinghouse believes that gap re-opening will not lead to fuel rod failure

..4 f-Gap Re-Opening Scenario Bounding Rod Performance Analysis Bounding :llel rod performance scenario analyzec.

as a pre-condition to design basis events Simu ated bounding duty rod using conservative assumptions (to bound a 1 plants anc. consic er key uncertainties):

- cladding oxidation at upper limit 1 - upper bound fission gas release

- lower aound oxide thermal conductivity

- degraded UO2 thermal conductivity

. .. J Gap Re-Opening Scenario Bounding Rod Performance Analysis Gap re-opening localized to a few inch segment at point of worst corrosion auildun (a aout 10 feet up)

Slow increase in pellet-clad gap wita continuec operation Slow aeatup of pel ets in that area c.ue to gap's additional thermal resistance Ac.ditional gas release from these pellets due to notter temperatures .

'e Gap Re-Opening Scenario Bounding Rod Performance Analysis Bounc.ing duty rod simulation showed:

- small gap re-opening (less than initial BOL gap)

- increased rod internal pressure

- increased local pellet temperature Monte-Car. o simulation of probaole 95%

uncertainty combinations saows that safety analysis reference case is conservative l

Temperature increase offset somewhat ay natural l power burndown of:1ig1 burnup fuel rods l

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q Safety Evaluation Assuming Gap Re-opening Pre-condition of hotter roc s and higher internal pressures were consic ered in each design basis transient event (Condition I, II, III, and IV)

All transients occur too rapidly to see any change in gap re-opening via creep out No new accident scenarios are created ay.the gap re-o;pened condition

~ ^ ^

Safety Evaluation Assuming Gap Re-opening e -

All aspects of plant safety analyses remain bounding @OCA, Non-LOCA, T/H, Core Design, Fuel Rod. Design), except for:

- potential to exceed no gap re-opening design limit

- with potential gap re-opening, possibility to also exceed 17% LOCA metal wastage criteria Gap re-opening does not necessarily imply

that 17% LOCA limit will be exceeded

Safety Evaluation 3 Gap Re-opening Summary 4

Gap re-opening does not lead to fuel failures t 5 l Gap re-opening does cause eleval:ed temperatures and pressures in high duty rods Gap re-opening does not cause previously analyzed ~ design basis accident scenarios to become worse Gap re-opening is oflow safety significance

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4 ** $

Safety Evaluation 17% Local Oxidation Criterion - Background

- 10CFR50.46 Acceptance Criteria for PCT and local oxidation, in combination, established to limit embrittlement and potential for fbel fragmentation during quench Fragmentation tied to coolable geometry requirement

- Tests used to define limits were not representative of high burnup fuel

- pre-transient oxidation

- irradiation effects

- W has interpreted 10CFR50.46 limit on maximum local oxidation as applying to pre-transient plus transient oxidation

i i Safety Evaluation  !

l Recent French Experiments Performed with l Irradiated & Corroded Data L

- Reported at 1996 Water Reactor Safety Meeting (NUREG/CP-0157, Vol.1, pp 161-172)

- Cladding samples taken from 5-cycle fuel with average rod burnup of 60 GWD/MTU

- 30 tests performed,25 retained / reported i

~80% from mic.-core elevations (oxide thickness 50-70 microns, equivalent to 6-8% initial cladding oxidation) 4

~20% from limiting (high) elevations (oxide thickness 60-t 120 microns, equivalent to 7-14%)

l - Single and double-sided oxidation experiments performed

Safety Evaluation .

Recent French Experiments Performed with Irradiated & Corroded Data t

Assessment of" failed" samples performed conservatively

- few samples visibly cracked or fragmented

- internal overpressure applied while sample immersed in water, observation of gas bubbling considered to be failed cladding l

i No failures observed with <17% transient oxidation (in addition to pre-transient oxidation)

- Failure limits of 23% total oxidation (pre-tran-ient + transient) l observed for single-sided oxidation,33% for two-sided

Safety Evaluation LOCA Assessment of Gap Re-opening Scenario Generic in nature, no plant-specific calculations performed Used existing sensitivity studies to estimate effects on PCT and

, local oxidation Conicusions:

10CFR50.46 criteria satisfied for small break LOCA

- Local oxidation criterion may be exceeded by a small amount for large break LOCA, primarily due to pre-transient oxidation. PCT criterion would continue to be met I

l - French data support the conclusion that the safety significance is low

.... 4 Safety Evaluation

Additional LOCA Efforts to Date Goal: calculate incremental oxidation due to LOCA, for gap re- i opening scenario Limited scope parametric studies performed using approved best-estimate large break LOCA codes WCOBRA/ TRAC - predicts system thermal-hydraulic response, provides fluid conditions for detailed assessment of limiting location in the core

- HOTSPOT - analyzes limiting location in the core

i Safety Evaluation Additional LOCA Efforts to Date l

WCOBRA/ TRAC parametric studies

- Selected top-skewed power shape with peak at elevation of.

interest

- Scaled power distribution to reflect reduction in achievable i

power .

- Increased fuel temperatures to account for fuel thermal conductivity degradation with burnup L -

! ....)

9 Safety Evaluation Additional LOCA Efforts te Date HOTSPOT parametric studies modeled maximum pre-transient oxide thickness (restricts allowable transient oxide to 2% of oxide thickness) varied initial fuel temperature (fuel thermal conductivity multiplier added as an option) varied local KW/Ft l " time scale stretching" applied l

l

Safety Evaluation Gap Re-opening Study - LOCA Results for ,

15x15 Fuel IJOCA CASE ATFUEL PCT BDBURSI? %OXII7N REFERENCE (BOL) 0 15/6 NO 20%BURND0%N -230 1649 YES 0.9 ,

t 20%BURNDOMN,+200F -20 1816 YES 1.7 i DECREASEDKFUEL 4480 1871 YES 23

-1.2 KWFf -180 1695 YES 1.1 30%BURNDOWN,+200F -180 1617 YES 0.7

. . .. q Safety Evaluation Gap Re-opening Study - LOCA Results for 17x17 Fuel LOCA CASE TFUEL PCT BD BURST? % OXID'N l

REFERENCE A (BOL) 0 1936 NO

-220 1549 YES 0.9 20% BURNDOWN l

20% BURNDOWN,+200F -20 1627 YES 1.7 DECREASED KFUEL +770 1862 YES 2.8

~

-1.C KW/FT 1600 YES 1.3 REFERENCE B (BOL) 0 2114 NO 20% BURNDOWN,+200F 0 1661 YES 1.9

+ C.4 KW/FT, AKFUEL +150 1749 YES 2.7

...4 e

Safety Evaluation LOCA Conclusions LOCA assessment confinned to be conservative

- Ac c.ed confic ence that safety significance is low

- Reasona ale method for assessing incremental LOCA oxic.ation for gap re-opening scenario has been

~

. deve. oped

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.,.-l Regulatory Compliance L

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a . .. )

l Screening Criteria to Address Compliance 1 Plants in the 1st half of their operating cycle or returning from an outage are allin compliance 2 Plants in the latter half of their operating cycle may have gap re-opening 3 All plants predicted to have gap reopening, but which have

. pre-oxidation < ~12% (based on latest corrosion model) are in compliance Based on current information, which needs to be verified, all plants except one pass the screening criteria today. The exception would likely show acceptable results, but ramping down today to enter normal refueling outage

Screening Criteria to Address Compliance In approximately 1 monta, a limited number of plants may exceec the oxidation screening criteria.

These plants will be assessec prior to prec.icted date of exceeding the screening criteria This assessment will be performed based on the described sensitivity methodology with plant specific conditions t

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Long-Term Plan for Resolution Step 1 Review & Improve Analytic Models

- Assigned full-time team of dedicated incividuals to review fuel performance metaodology and models (on-going)

- 1/98: complete top-to-bottom review of

~

methods and models

- 3/98: c.evelop program plan L/98: meet with 3RC to review program plan

- 7/98: modify PAD coc e and methods

Long-Term Plan for Resolution z

Step 2 Gather Ac ditional Data to Validate Fuel Performance Methods

- 11/97: ic.entify what additional data collection woulc be beneficial and develop plan for collection -

- 12/97 to 5/98: complete on-site inspections l

O* '. 0 2 Long-Term Plan for Resolution Step 3 Plant-by-Plant Assessments

- 12/97: design new fuel assemblies to ensure adequate rod internal pressure margin exists for each plant's intended duty scenario .

- 7/98: begin formal plant-by-plant assessments to show that limits are met with modified PAD code using plant-specific margins

O 'a . ]

WOG Involvement Current Dialog Licensee Event Report Future Interactons

__ __m _______ __ m _ _ _ _ _ __ - _ . - . _ _ _ _ _ _ _ _a

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Westinghouse Owners Group cc:

Mr. Nicholas Liparulo Westinghouse Electric Corporation i Mail Stop ECE 415 l P.O. Box 355 l P#ttsburgh, Pennsylvania 15320-0355 Mr. Hank Sepp Westinghouse Electric Corporation Mail Stop ECE 447A P.O. Box 355 Pittsburgh, Pennsylvania 15320-0355 P

Mr. Andrew Drake Westinghouse Owners Group .

Westinghouse Electric Corporation

Mail Stop ECE 516 ,

P.O. Box 355 Pittsburgh, Pennsylvania 15320-0355 ,

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