ML19291C126

Concurs W/Westinghouse Position That Current ECCS Models Are in Commpliance W/App K,10CFR50.No Reduction in Present Peaking Factor Required.Evaluation & Affidavit Encl

ML19291C126
Person / Time
Site:	Beaver Valley
Issue date:	01/17/1980
From:	Dunn C DUQUESNE LIGHT CO.
To:	Eisenhut D Office of Nuclear Reactor Regulation
References
TAC-12673, NUDOCS 8001220291
Download: ML19291C126 (6)

Text

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15219 January 17, 1980 Director of Nuclear Reactor Regulation United States Nuclear Regulatory Commission Attn: D. G. Eisenhut, Acting Dit.ctor Division of Operating Reactors Washington, D.C. 20555

Reference:

Beaver Valley Power Station, Unit No. 1 Docket No. 50-334 Response to Letter Concerning Fuel Cladding Swelling and Rupture in ECCS Evaluation Models Gentlemen:

Enclosed are three (3) signed originals and thirty-seven (37) copics of the Duquesne Light Company response tu your letter dated November 9, 1979.

We have reviewed the material relating to fuel cladding strain and fuel assembly flow blockage and have determined that, based on the results of the evaluation included with the letter, no reduction to the present peaking factor is required to comply with 10 CFR 50.46 for the interim period during which the NRC conducts its review of the Westinghouse ECCS model improvements.

Based upon the information supplied herewith, including such credits which are derived from improvements to Westinghouse's ECCS analytical model, Duquesne Light Company concurs with the Westinghouse position that current Westinghouse models are conservative and are in compliance with Appendix K, 10 CFR Part 50.

Very truly yours,

?

C. N. Dunn Vice President, Operations cc: A. Schwencer, Chief Operating Reactors Branch No. 1 Division of Operating Reactors } -[, b h _), } h Washington, D.C. 20555 8001220 2hl

' (CORPORATE SEAL)

A ttes t:

TJt-si k H. W. Staas Secretary-COMMONWEALTH OF PENNSYLVANIA)

) SS:

COUNTY OF ALLEGIENY )

On this /8 ' ~ day of t/ 4AWx/ , 1980, before me, towarn w ernuwn,

~~

, a Notary Public in and for said Commonwealth and County, personally appeared C. N. Dunn, who being duly sworn, deposed, and said that (1) he is Vice President of Duquesne Light, (2) he is duly authorized to execute and file the foregoing Submittal on behalf of said Company, and (3) the statements set forth in the Submittal are true and correct to the best of his knowledge, information and belief.

//. ~ < L py ? W k.N.n,, n .

DONALD W. SHANNON. NOTARY PUBLIC PITTSBURCH. ALLEGHENY COUNTY MY COMMIS$60N EXPIRES JUNE 7,1983 Member, Pennsylvanu Assocuten of Notaries 1788 317

Attachment A. Evaluation of the potential impact of using fuel rod models presented in draft NUREG-063C on the Loss of Coolant Accident (LOCA) analysis for Beaver Valley Unit 1.

This evaluation is based on the limiting break LOCA analysis indentified as follows:

BREAK. TYPE - DOUBLE ENDED COLD LEG GUILLOTINE ,

BREAK DISCHARGE COEFFICIENT = 0.4 WESTINGHOUSE ECCS EVALUATION MODEL VERSION - Modifed* February 1978

• The fuel rod burst model was modified to factor in heatup rate dependence as documented in WCAP-8970-P-A " Westinghouse Emergency Core Cooling System Small Break, October 1975 Model. Fuel rod burst curves used in this analysis represented clad heatup rates of 10*F for the llot Rod and 10"F for the Average Hot Assembly Rod.

CORE PEAKING FACTOR - 2.32 IIOT ROD MAXIMUM TEMPERATURE CALCULATED FOR THE BURST REGION OF THE CLAD - 1880*F = PCT B

ELEVATION - 6.0 Feet 110T ROD MAXIMUM TEMPERATURE CALCULATED FOR A NON-RUPTURED REGION OF Tile CLAD - 2192*F = PCT N

ELEVATION - 7.5 Feet CLAD STRAIN DURING BLOWDOWN AT TilIS ELEVATION 0.45%

MAXIMUM CLAD STRAIN AT TilIS ELEVATION - 2.3%

Maximumtemperatureforthismodeoccurswhenthecorereflood$ateis LESS than 1.0 inch per second and reflood heat transfer is based on the STEAM COOLING calculation.

AVERAGE HOT ASSEMBLY ROD BURST ELEVATION - 6.0 Feet IIOT ASSEMBLY BLOCKAGE CALCULATED - 46.8 Percent

. 1. BURST NODE The maximum potential impact on the ruptured clad node is expressed in letter NS-TMA-2174 in terms of the change in the peaking factor limit (FQ) required to maintain a peak clad temperature (PCT) of 2200*F and in terms of a change in PCT at a constant FQ. Since the clad-water reaction rate increases -ignificantly at temperatures above 2200*F, individual effects (such as APCT due to changes in several fuel rod models) indicated here may not accurately apply over large ranges, but a simultaneous change in FQ which causes the PCT to remain in the neighborhood of 2200*F justifies use of this evaluation procedure.

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Attachment Page 2 From NS-TMA-2174:

For the Burst Node of the clad:

0.01 AFQ = % 150*F BURST NODE APCT

- Use of the NRC burst model could require an FQ reduction

, of 0.015

- The maximum estimated impact of using the NRC strain model is a required FQ reduction of 0.03.

Therefore, the maximum penalty for the Het Rod burst node is:

APCT y = (.015 + .03) (150*F/.01) = 675*F Margin to the 2200*F limit is:

APCT 2

= 2200*F - PCTB ~

The FQ reduction required to maintain the 2200*F clad temperature limit is:

AFQ B

~

l~ 2

(* O 150*F

= (675 - 320) (.01) 150

= 0.024

2. NON-BURST NODE The maximum temperature calculated for a non-burst section of clad typically occurs at an elevation above the core mid-plane during the core reflood phase of the LOCA transient. The potent-tial impact on that maximum clad temperature of "ng the NRC fuel rod models can be estimated by examining two aspects of the analyses. The first aspect is the change in pellet-clad gap conductance resulting from a difference in clad strain at the non-burst maximum clad temperature node elevation. Note that clad strain all along the fuel rod stops after clad burst occurs and use of a different clad burst model can change the time at which burst is calculated. Three sets of LOCA analysis results were studied to establish an acceptable sensitivity to apply generically in this evaluation. The possible PCT increase resulting from a change in strain (in the Hot Rod) is +20*F per percent decrease in strain at the maximum clad temperature locations. Since the clad strain calculated during the reactor coolant system blowdown phase of the accident is not changed by the use of NRC fuel rod models, the maximum decrease in clad strain that must be considered here is the difference between th9 " maximum clad strain" and the " clad strain during blowdown" indicated above.

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Attachment Page 3 Therefore:

APCT 3 ~ (20*F.01 strain)S (M IN - STRAIN)

=(, 1) (.023 .0045)

= 37'F The second aspect of the analysis that can increase PCT is the flow blockage calculated. Since the greatest value of blockage indicated by the NRC blockage model is 75 percent, the maximum PCT increase can be estimated by assuming that the current level

. of blockage in the analysis (indicated above) is raised to 75 percent and then applying an appropriate sensitivity formula shown in NS-TMA-2174.

Therefore, APCT4 = 1.25*F (50 - PERCENT CURRENT BLOCKAGE)

+2.36*F (75-50)

= 1.25 (50 - 46.8) + 2.36 (75-50)

+ 63*F If PCT urs when the core reflood rate is greater than 1.0 N

inch per second APCT = 0. The total potential PCT increase forthenon-burstnokeisthen APCT ~ + "

5 3 4 Margin to the 2200*F limit is

~ ~

APCT ~

6 N The FQ reduction required to maintain this 2200*F clad temperature limit is (from NS-TMA-2174)

AFQ N = ( PCT S

- 6 (1 F PCT}

~

AFQ

• N The peaking factor reduction required to maintain the 2200*F clad t.emperature limit is therefore the greater of AFQ #"

B AFQ N

or: AFQPENALTY ~ *

/

1788 320

Attachment Page 4 B. The effect on LOCA analysis results of using improved analytical and modeling techniques (which are currently approved for use in the Upper Head Injection plant LOCA analyses) in the reactor coolant system blowdown calculation (SATAN computer code) has been quantified via an analysis which has recently been submitted to the NRC for review.

Recognizing that review of that analysis is not yet complete and that the benefits associated with those model improvements can change for other plant designs, the NRC has established a credit *that is acceptable for this interim period to help offset penalties resulting from application of the NRC fuel rod models. That credit for two, three and four loop plants is an increase in the LOCA peaking factor limit of 0.12, 0.15 and 0.20 respectively.

C. The peaking factor limit adjustment required to justify plant operation for this interim period is determined as the appropriate AFQ credit identified in Section (B) above, minus the AFQ ca culated in Section (A) above (but not greater than zero). PENALTY FQ ADJUSTMENT = 0.15 - 0.092

. -0

/

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