ML19093B036

Enclosed New LOCA-ECCS Analysis with New Fq Limits to Ensure LOCA-ECCS Acceptance Criteria Delineated in 10 CFR 50.46 Is Met

ML19093B036
Person / Time
Site:	Surry
Issue date:	04/07/1978
From:	Stallings C Virginia Electric & Power Co (VEPCO)
To:	Case E Office of Nuclear Reactor Regulation
References
Serial No. 197
Download: ML19093B036 (6)

Text

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-~vepco_

April 7, 1978 t/j;:;;

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Mr. -Edson G. -Case Serial No::~;1~7 ~;,. *

-office. of _Nuclear Reactor ~gulati~n :

• FR/MLB :crl. ;; .

Attn: Mr. Albert Schwencer, : Chief Docket Nos. ..z:; -

50-2802 Operating_Reactors Branch No~ 1 so..:.2s1 *

..

• Division of Reactor Licensing License*.Nos~ DPR-32 U~ S. Nuclear Regulatory_Commission* DPR'."'37 Was-hington; D. C.- - 20555.

• Dear_ Mr. Case 'i .

_ Pursuant to the provisions of.the Surry Units.No. 1 and 2 Technical Specifications, the. NRC ~gion II 'Was notified on March 23, : 1978 of an error ..

in the *currently applicable ._LOCA..:.Eccs analysis. The* error foµnd was in -the *

._ representation of the heat reiease froni the metai-water react'ion in the NRC approved Westinghouse* LOCA-ECCS evaluation -*model. The. impact of this* error

• is-to- increase the ,peak _clad_ tempera.ture ob-tained during a* postulated LOCA _

over -that* reported in the currently applicable LOCA-ECCS an~lysier. _ -To con-*

• servati_vely accommodate the impact of this error, the LOCA-ECCS limiting, -

- heat _ .flux hot channel £_actor - (F~) has been administratively *reduced from-its -'present Technical* Specifications_ limit* of 1. 85 to 1. 81 (or to 1.79 when

. additionaLsteam_ generator tube pluggiJ,'lg is required). - These new FQ .limits have b'een conservatively selected* in order to ensure that the LOCA;..ECCS.

,acc*eptailce criteria delineat~d _in. 10 CFR 50. 46. is met. The -bases . for the

.: *,new* Fq t~nd ts _a_r~ .provided _* i11 -the Attachment *.

-* * * :_ *compliance w:i.th the new FQ limit will be *eils~~ed by the _performance of axial power distribution mo_nitor!ng (APDM) as described iri-.th~ 'l'echni_cal

• Specif'ica.~ions.* A~ministrative instructions.have been implemented that.require APD~f shrveillance for power- operation above-:_ 82% -for Unit. *1 and 85% -for Unit 2 *.

Additiorially, the~I operating 111.mitei (for operation-outside*of the constant axial'offset*control target* banci) have been revised in order-to ensure a: con-sistent basis between constant axial offset control of* the core: and' the "*Jl'.Q sur..:.- _-

veillanc~ requirements. These administrative restrictions will *remain in effect* -

until*a new LOCA-ECCS analysis :and associated changes-to the Technical Specifica-tions. are approved. - .

. The new LOCA-ECCS analysis wil.i -be performed as soon as possible with an *acceptable Westinghouse LOCA-ECCS' evaluation .modei. This new_ analysis will -

be in compliancewith 10 CFR 50, Appendix Kand meet the acceptance criteria of 10: CFR 50.46. .

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Should' you h~ve *questions, we would iike. **t.o meet with you at. your earliest convenience.

• Stalling e President

• Production Atfacbment

'cc: l-h". 'Jams P. - O'Reilly~ Director.*

Office of >In.spection .and Enforcement**

Re.g:i.on II ..

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I 1*

e ATTACHMENT 1

e TABLE 1 CALCULATION OF FQ LIMIT FOR SURRY UNITS NO. 1 AND 2 : ....

Current Fq LIMIT 1.85 IMPACT OF CODE ERROR (~FQ) -0.2 (See Note 1)

ADDITIONAL CREDITS (~Fq) +o.158 (See Note 2) or +0.135*

NEW Fq LIMIT 1. 81 or 1. 79*

• Value contingent upon steam generator plugging level exceeding current limiting level unless additional analysis is performed.

NOTE 1 EXPLANATION OF METAL-WATER REACTION PENALTY A code error involving a logic inconsistency has been found in tw_o of the computer codes used in the Westinghouse LOCA-ECCS Evaluation Model.

This logic inconsistency involves the interface between the zirconium-water reaction heat generation calculation and the heat conduction equation. Both the zirconium-water reaction equation (Baker-Just) and the heat conduction equation are solved correctly. However, the heat conduction equation uses a volumetric heat flux from the zirconium-water reaction calculation. The output of the zirconium-water reaction calculation is a surface heat flux.

This surface heat flux is modified by dividing by the thickness of the radial mesh size between the surface temperature node and the first node inside the clad to obtain a volumetric heat flux. It is this calculation which was performed incorrectly. The inconsistency underestimates the volumetric heat flux due to zirconium-water reaction by a factor of 2. The effect of this error has been assesed and it has been determined that a penalty of 0.20 in Fq conservatively bounds the impact.

. e NOTE 2 EXPLANATION OF CREDITS Several credits have been identified to offset. the adverse effects of the corrected metal-water reaction heat release. The individual components com-prising the total credit are discussed below.

1) 15 X 15 FLECHT Heat Transfer Correlation - The FLECHT heat transfer correlation is used during the reflood portion of a postulated LOCA. New 15 X 15 heat transfer test data has been incorporated with the original FLECHT data, and the resulting modified FLECHT heat transfer correlation has been used in generic (Surry was the analyzed plant) sensitivity studies. These studies indicate that the modified correlation conservatively results in a benefit in FQ of at least 0.06. *

2) Margin to Peak Clad Temperature - The current LOCA-ECCS analysis for the Surry plants (see Vepco to NRC letter, Serial No. 372 dated August 26, 1977) results* in a peak clad temperature of 2177°F. Westinghouse generic sensitivity studies indicate that the 230F margin to the PCT LOCA limit of 2200°F represents a conservative benefit in FQ of at least 0.02.

3) Containment Back Pressure Margin - Essentia'lly all of the surfaces, in the containment building, with the exception of stainless steel surfaces, are painted. The paint acts as an additional thermal resistance for the heat flow to the containment heat sinks which results in higher containment back pressure and a benefit for the LOCA-ECCS analysis. Westinghouse sensitivity studies for steam cooling plants (i.e. Surry) on the effect of painted surfaces in the contain-.

ment building indicate a conservative benefit in FQ.of at least 0.03.

4) Steam Generator Tube Plugging - The current LOCA-ECCS analysis assumed a steam generator tube plugging level of 25%. Consequently, the margin between the actual steam generator tube plugging level and the level assumed i~

the current analysis represents a potential benefit. This benefit was conserva-tivel~ determined by Westingho~se to.rep:esent 0.023 in F0 for the lim~tin~ ~c~ual plugging level of the Surry units which is currently 20.8?o. Should this limiting actual plugging level be exceeded in the future, the steam generator plugging credit will be deleted (or revised based on additional.analysis).

5) Fuel Pellet Temperature Margin - The current LOCA-ECCS analysis initial stored energy conditions were based on limiting generic fuel pellet tempera-tures. The as~built Surry fuel parameters are less limiting than the values assumed for the generic case. Consequently, the actual Surry fuel pellet temperatures are less than the temperatures assumed in the current analysis which results in a con-servative benefit in FQ of at least 0.025.