ML20091Q322

Summarizes Status & Open Issues Remaining for Facility Frosstey Code

ML20091Q322
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	12/23/1991
From:	Beyer C PACIFIC NORTHWEST RESEARCH CENTER
To:	Wu S Office of Nuclear Reactor Regulation
Shared Package
ML20091Q328	List: ML20091Q322
References
NUDOCS 9202040323
Download: ML20091Q322 (4)

Text

- _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

EnClO$ure OBattel!e e.u u u mm.m o-m toim.

.u. n e,.,~

s' ( ) $..a

'-J W i e.im y'

4:U

', eM e r

(.,

6, i

December 23, 1991 Dr. 5. L. Wu Peactor Systems Cranch Office of Nuclear Peactor Regulation U.S. huclear Regulatory Commission fiail Stop 8E23 Washington, DC 20555

Dear Shih Liang:

This letter is intended to summarize the status and the open issues that remain with the Vermont Yankee flucle r Power Corporation (VYliPC) submittal of the FROSSTEY code.

The open issue that remains in this review is in the conscrvatisms that need to be applied in FR0551EY2 code licensing analyses.

This iLLue was first raised in f4RC's letter dated March 9, 1990 (Referente 1) requesting further information.

The licensee provided a written response to Reference 1 in a letter dated March 6, 1991 (Reference 2) that was found to not adequately address the issue of conservatisms for FR0551EY2 licensing analyses.

A lett.r was prepared by PNL dated Augus* 19, 1991 that addresstd the conservatisms that need to be included in fuel performance code licensing analyses.

This letter was forwarded to the licensee for their information.

Discussed during a conference call on October 28, 1991, ar.ong VYNPC, NRC, and PNL consultants was how VYliPC intended to address the open issue; however, the VYflPC verbal response has t een found t, be inadequate for the reasons cited in this letter.

As noted in my August 19, 1991 letter to you, industry LOCA analyses have traditionally included the uncertainties in the fuel perfornance code input e.g.,

dimensional uncertainties in fabricution of fuel rods, uncertainties in the fuci performance code calculation itself, and any biases that may exist in the code.

Also noted in my previous letter, the conserva-tisms used by industry for LOCA analyses in the recent past have been such that there has been a 95% probability at a 95% confidence level that the predicted LOCA stored energy will be bounding.

VYNPC staf f suggested in the las' conference call held on October 28, 1991.

that based on their sample calcuhtion for a boiling 1w),er rcactor (BWR) design, provided in their fiarch 1991 response to questions, the FR0551EY2 code i,put uncertainties fnr commercially-fabricated fuel rods for licensing aralyses such as LOCA are equal *o or greater than the code calculational untcrtainties, VYNPC staff appear to be suggesting that the fR0551EY2 licensing input for the code satisfactorily covers the conservatisms necessary for 10CA stored energy and that the uncertainties in the FROSSTEY2 code 10104D$1)

CBattelle Or. 5. t. Wu December 23, 1991 Page 2 calculations do not need to be considered.

I have evaluated this clam tw the VYNPC staff and have concluded that there are several problems with ine:*

claim.

First, the translaticn of code input uncertainties to the uncertaintir m

fuel stored energy is of different magnitudes for different fuel designs The greatest differences exist between pressuritea water reactor (PWR) and hlR fuel designs.

ViNPC staff have indicated that they intend to apply IR0551[i2 t_o both PWR and OWR designs.

Therefore, the calculated uncertainties in [AR fuel stored energy as induced by BWR fuel input uncertainties are not applica-ble t0 input induced uncertaintles in PWR fuel stcred energy.

Second, ry own assessment of the uncertainties in the FR0551EY2 code com pari'ans to experMntal dat a suggests that the standard deviation, o, of this comparison, in tei is of stored energy, is approximately equal to the increase in stored energy ( hove the best estimate value) induced by the BWR commercial rod input uncertai v es to FR0551EY2.

1herefore, the conservatism in the f R0557[i2 calculatea stored energy resulting f rom the VYNPC proposed licensing input of CWR com~ercial rod dimensional uncertainties is significantly lets than the censervatism currently used by industry.

The level of conservatism currently used by indust ry is such that the LOCA stored energy will be bounding based on a 9 W probability at a 95% confidence level including both input and code calculational uncertainties.

Third, the LOCA uncertainties for stored energy should ideally include both the uncertainties in the commercial fuel rod dimensions, i.e., c' (comercial fuel rod input), plus the uncertainties in the IR055TEY2 code calculation, i.e., c' (FR0551E G code).

The letter uncertainty is difficult to determine because the uncert ainties in the TR05STEY2 code co parisons to experiment al data inherently includes the uncertainties in the f abr ication of the experi-mental fuel rods [o'(experimental rod input)), uncertainties induced by the experiment (c (experinent)], and TR0551EY2 calculational uncertainties

[c'(f e0551EY2 code)],

VYNPC staff have assured that the dimensional uncertainties of the experi-mental fuel rods plus the other experimental uncertainties are much greater than the f R055TEY2 calculational uncertainties (i.e., c'(experirental rod input) 4 o'(experiment) no'(f R05STEY2 code)) and, therefore, they can ignore the IR055TEY2 calculational uncertainties.

It is pore likely that c'(f R0551[Y2 tode) a (experinental rod input) + o'(experirent ).

The V.4PC assumption also assu es the centercial rod input (fabrication) unccetainties are equal tn thnse for the experimental fuel rods plus the 0ther e merirental uncertainties.

1 do not believe the VYNPC assumption is valid because the input dirensional untertainties for the experimental rods are significantly 1ower than f or commercially f abricated rods because the former input, in most cases, is based on the actual mean measured dimensions and f abrication charac-teristics of the esperimental rods following fabrication.

Therefore, the input uncertainties for the experimental rods are significantly less than for commercially-fabricated rods.

In addition, experieentally-induced uncertain-l ties are hard to determine

CBattelle or s. t. wu Decevbcr 23, 1991 page 3 f er your background informatien, the only instance in the past where fM appreval was provided for a fuel vendor's fuel perfortrance code for calcu-lating LOCA stored energy using only code input uncertainties as proposed by VyNrC staf f, was for a code that had a large conservative bias in calculated storrd energy that bounded the uncertainty in the coic's prediction.

Thi: 15 net the case for the FROSSIEY2 ccde because it s thereal predictions are considercd to be best est1~3te although the code appears to provide a so"wnat conservative prediction of fission gas release.

Pascd on the above discussions, I continue to recom end that FR05SilY2 includo the conservative ap; roach for LOCA stored energy as discussed in ny August 19, 1991 letter to you.

Licensing analyses of end of life rod internal pressures should normally include uncertainties in input due to variabilities in fabrication, t,ut al>c the uncertainties in the FROS57EY2 predictions of fission gas release.

The uncertainties in the code's thermal predictions does not need to be included because this is incorporated in the fission gas release prediction uncertain-ties.

The rod internal pressure calculations should also include transients up to the linear heat generation, rate technical specification limits.

The transients should be included throughout the life of the fuel rod and their number should bound those possible during normal operation and anticipated operational occurrences.

The fuel melting calculation should not only include fabrication uncertainties

~

but should also include those transients from anticipated operational oc-currences and include the effects of fission 9as release during these transients on the code ther"al predictions.

It is ant ic i;:ated that additional review will be required once we rece1',e ViNpC's response on how they intend to handle FROSST[Y2 code input and calculational uncertainties for licensing analyses.

If you have questions on the above, please feel free to call Pe.

Sincerely,

/

79-

/

Carl o ceyer Reactor Syste"s and fuel perfermance Section CEB ost cc:

M Thomas. NRC

OBattelle

.. <. eu F: erber 23, 199}

f

.g e 4 4

Ellififil5

\\

1.

Letter, U.S. flutlear Kegulatory Commission to Vermont Yankee Nuclear Power Corporation (!JVY 90 05)) dated March 9, 1990, 2.

etter. Vermont Yankee fluclear Power Corporation to U.S. flucl.,

e9u at ory C omms p.10h (BVY 91-024) dated March 6, 1991, w

a w

-h

i s

e Docket t!o. 50 271 January ?d, I'm?

Mr. L. A. Tremblay Licensing Engineer Vermont Yaph e hutiear Power Corporation 580 Main Street Bolten. Massachusetts 01740 1398 Pear Mr. Tremblay:

SUBJECT:

OPEN ISSUES ON FROSSTEYF CODE (TAC I:C. P08?16)

Enclosed is a sumary report from our cortultant Battelle Pacific florthwest Laboratories (PNL) concerning the open issues of the fr0SSTEY2 code review following a conference call between Vermont Yankee Nuclear Power Corporation arid NRC on October 28, 1991. We endorse our consultant's findings, and this sumary report constitutes our position on FROSSTEYP.

Sincerely.

Original signed by:

Patrick Sears, Project Manager Project Directorate 1 3 Division of Reactor Projects 1/11 Office of Reactor Regulation cc w/ enclosure:

See next page 01STRIBUT10N Docket No. [S0 271)

NRC & Local PDRs F01 3 Reading S. Varga J. Calvo W. Butler P. Sears H. Rushbrook OGC ACR$(10)

C. Hehl, Region 1 R. Lobel

'7

/D#

OFC.

LA:PDI-3

THQDI.3

D:PDlg

W h y d,. /..~..:..............

...... :. h f

...... :. r.fg.........:............................:..............:..............

RJ[nIs/

NAME

MR f

k

PSears:sk

(:WRBu r

) /[/92

\\ /J/9?

//gj(92 DATE 7 / t')/92 OfP1CIAL RE00FD COPY t/

Document Name:

VY TPEl1 BLAY M68216

e Mr. L. A. Tremblay, Senior Licensing Vennont Yankee Engineer Cc!

tir. A Gary Weigand G. Dana Disbee, Esq.

President & Chief Executive Officer Office of the Attorney General Vennont Yankee fuelear Power Corp.

Invironmental Irotection Eureau R.D. 5. Box 169 State House Arnex ferry Reed 25 Capitol Street Brattleboro, Vernant 05301 Concord, t.'ew Hantpshire 033014m Mr. John DeVincentis Vice Pres' dent Mr. James Pelletier Yankee Atomic Electric Company Vice President - Erigineerirt

$80 Main Street Vennent Yankee fiuclear Power Corp.

Bolten Massachusetts. 01740-1398 P. O. Box 169, Ferry road Brattleboro, Vermont 05301 Regional Administrator, Region !

U. S. Nuclear regulatory Comission Resident inspector 475 Allendale Read Vermont Yankee Nuclear Power Station King of Prussia, Pennsylvania 19406 U.S. Iluclear Regulatory Comission P. O. Box 17; R. K. Gad, 111 Vernon, Vermont 05354 Ropes & Gray One Internationel Place Chief, Safety Unit Boston, Massachusetts. 02110-2624 Office of the Attorney General One Ashburton Flace, 19tn floor Mr. W. P. Murphy, Senior Vice President, Boston, Massachusetts 02108 Operations Vermont Yankee fluclear Power Corporation Mr. David Rodham, Director R.D. 5, Box 169 Massachusetts Civil Defense tgency Terry Road 400 Worcester Road Brattleboro, Verment 05301 P.O. Box 1496 framingham, Massachusetts 01701 0317 Mr. Pichard P. Cedano, Comissioner ATith James Muckerheide Vermont Department of Public Service 120 State Street, 3rd Floor Montpelier, Vermont 05002 Public Service Board State of Vermont 120 State Street Montpelier, Vermont 05602 Chairman, Board of Selectmen Town of Vernon Post Office Box 116 Vernon, Vermont 05354-0116

. Mr. Raymond 11. ficcandless Vermont Division of Occupational and Radiological Health Administration Buildirg Montpelier, Vermont 05602

CnclosUre OBattelle r o m %,o n

., m, m i,c,

%,,,* e,,,,,, m

() t'. 4

'4 y,~,-,u w

on w

Decceer 23, 1991 Dr. S. L Wu Peacter Syste s Franch Office of Nuclear Reactor Regulatien U.S. flutlear Regulatory Commission fiail Stop EE23 Washington. DC 205$5 Dea, Shih Liang:

This letter is intended to summarize the status and the open issues that remain with the Vermont Yankee Nuclear Power Corporation (VYllPC) submittal of the FROSS10Y code.

The open issue that remains in this review is in the conservati:es that need to be applied in FR0551[Y2 cooe licensing analyses.

1his issue was first raised in NRC's letter dated March 9, 1990 (Reference 1) requesting further information.

The licensee provided a written response to peference 1 in a letter dated flarch 6, 1991 (Reference 2) that was found to not adequately address the issue of conservatisms for FROSSTEY2 licensing aaalyses.

A letter was prepared by Pill dated August 19, 1991 that addrest?d the conservatisms that need to be included in fuel performance code licensing analyses.

This letter was forwarded to the licensee for their information.

Di* cussed during a conference call on October 28, 1991, among ViNPC, NRC, and Piu consultants was how VYNPC intended to address the open issue; however, the VYNPC verbal response has been found to be inadequate for the reasons cited in this letter, As noted in my August 19, 1991 letter to you, industry LOLA analyses have traditionally included the untertainties in the fuel performance code input, e.g.,

dimensional uncertainties in fabrication of fuel rods, uncertainties in the fuel performance e

..! calculation itself, and any biases thtt may exist in the code.

Also notou in my previous letter, the conserva-tisms used by irdustry for LOCA analyses in the recent past have been such that there has been a 95% probability at a 95% confidence level that the predicted LOCA stored energy will be bounding.

VYNPC staff suggested in the last conference call held on October 28, 1991, that bas 0d on their sample calculation for a boiling water reactor (BWR) design, provided in their March 1991 response to questions, the FR05SlEY2 code input uncertainties for commercially fabricated fuel rods for licansing analyses such as LOCA are equal to or greater than the code calculational uncertainties.

VYNPL staff appear to be suggesting that the FROSST[Y2 licensing input for the code satisfactorily covers the conservatisms necessary for LOCA stored energy and that the uncertainties in the IR0551EY2 code h '[Ol,D9 0 $ 7s b

QBattelle o,

s. t. wa Decenber 23, 1991 Page 2 calculattens do r.ot need to be considered.

I have evaluated th:s claim ty tne VifipC staff and have concluded that there are several problems with their claim.

first, the translaticn of code input ur:ertainties to the uncertainties o fuel stored energy is of different magnitudes for different fuel derigns.

The greatest differences exist between pressurized water reactor (pWR) and FWR fuel designs.

fiPC staff have indicated that they intend to apply FR05 STET 2 to both PWR In..WR designs.

Therefore, the calculated uncertainties in LA fuel stored energy as induced by BWR fuel input uncertainties are not applica-ble to input induced uncertainties in PWR fuel stored energy.

Second, my own assessment of the uncertainties in the FROSSTEY2 code com-parisons to experimental data suggests that the *,tandard deviation, o, of this co~parison, in terms of stored energy, is opproximately equa! to the increase in stored energ/ (above the best estimate value) induced by the BWR commercial red input uncertainties to FROSST[Y2 Therefore, the conservatism in the FR05STEY2 calculated stored energy resulting from the VYtJPC proposed licensing input of EWR commercial rod dimenstonal uncertainties is significantly less than the conservatism Currently used by industry.

The level of sonservatism currently ustd by industry is such that the LOCA stored energy will be bounding based on a 95% probability at a 954 confidence level including both input and code calculational uncertainties.

Third, the LOCA uncertainties for stored energy should ideally include both the uncertainties in the commercial fuel rod dimensions, i.e., c' (com ercial fuel rod inDut), plus the uncertainties in the FR0$$TEY2 code calculation, i.e., a- (FROSSTE Y2 code).

The lotter uncertainty is difficult to determine because the untert ain'.1es in the FR05STEY2 code compar isons to c <perimental data inherently includes the uncertainties in the fabrication of the esperi-mental fuel rods (c'(experimental rod input)], uncertainties induced by the experiment [r(experiment)], and fR055TEY2 calculational uncertainties W (FROSSTEf2 code)).

VYtJPC staff have assumed that the dimensional uncertainties of the experi-mental fuel rods plus the other experimental uncertainties are much greater than the FROS$1EY2 calculational uncertainties (i.e., o (experimental red input) + v (experiment) no'(FROSSTEY2 code)) and, therefore, they can ignore 2

the FROS!TEY2 calculational uncertainties.

It is more likely that 2

f(FROSSIEY2 code) g(experimental rod input) + O (experirent).

The VYfipC assumption also assumes the commercial rod input (fabrication) uncertainties are equal to those for the experimental fuel rods plus the other experimental uncertainties.

I do not believe the VYt4PC assumption is valid because the input dimensional uncertainties for the experimentai rods are significantly lower than for commercially-fabricated rods because the former input, in most cases, is based on the actual mean measured dimensions and fabrication charat-teristics of the experimental rods following fabrication.

Therefore, the input uncertainties for the experimental r-e significantly less than for Nentally-induced uncertain-commercially fabricated rods, in addition ties are hard to determine.

4 OBaHelle or. s. t. wu Decest'er T3,1991 Page 3 Fer your background information, the only instance in the past where fGC approval was provided for a fuel vendor's fuel performance code for calcu-lating LOC A stored energy using only code input uncertainties as proposed t>y VYNPC staf f, was for a code that had a large conservative bias in calcula'c-stored energy that bounded the uncertairty in the code's prediction.

This 1:

not the case fer the FROSSl[Y2 code t'etause its thermal predict tons are censidered to be test es t'-ate although the code appears to provide a se NMt conservative prediction of fission ga: release.

Based on the above discussions. I continue to recom end that FROSSifY2 include the conservative approach for LOCA stored energy as discussed in ry I.ugu;t l 's.

1991 letter to you.

Licensing analyses of end of life rod internal pressures should nor-ally include uncert ainties in input due to variabilities in f abrication, but also the uncertainties in the FROSSTEY2 predictions of fission gas release.

The uncertainties in the code's therral predictions does not need to be included because this is incorporated in the fission gas release prediction uncertain-ties.

The rod internal pressure calculations should also include transients up to the linear heat generation rate technical specification limits.

The transients should be included through:ut the life of the fuel rod and their nu-ber thould bound those possible during normal operation and anticipated operational ncturrences.

The fuel elting calculation should not only include f abrication uncertainties but should also include those transients fro 11 anticipated operational oc-currences and include the effects of fission gas release during these transients on the tode thermal predictions.

It is anticipated that additional review will be reoutred once we rece15e VYNPC's response on how they intend to handle FROSSTEY2 code input and calculational uncertair ties for licensing analyses.

If you have questions on the above, please feel free to call me.

Sincerely,

//

O cC7

,[

Carl E. Beyer Reactor Systems and fuel Perforrance Section CES: dst cc:

EE Thomas, NRC

QBaffelle or. s. t. wu De c emtier 23, 1991 i'a a o 4 E11LEl!ELS CoiciatYN'Ilv"l".N[')~# "I $ $ " N vl$ "t ' '"k '" ""' I " 8

io d (

ac

@f;iJTi:1llnes; ;gJge;j;;rg;gog,ijg;s. neoe.,

O