ML19331B962

Forwards Response to NRC 791109 Ltr Re Fuel Rod Burst Model, Improvement to Heatup Rate Prior to Burst Definition & Use of Credit from Improved Analytical & Modeling Techniques to Offset Effect of New NRC Model

ML19331B962
Person / Time
Site:	Farley
Issue date:	08/06/1980
From:	Clayton F ALABAMA POWER CO.
To:	Schwencer A Office of Nuclear Reactor Regulation
References
NUDOCS 8008130620
Download: ML19331B962 (5)

Text

9 Alabama Power Company 600 North 18th Street Post Office Box 2641 .

Birmingham. Alabama 35291 Telephone 205 323-5341

. L k L';;ojW,7,tf,nt Alabama Power the soutwn elecinc system August 6, 1980 ,

Docket No.50-36h Director of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission

. Washington, D. C. 20555 Attention: Mr. A. Schwencer JOSEPH M. FARLEY NUCLEAR PLART-UNIT 2 FUEL ROD BURST MODEL Gentlemen:

As a result of discussions with your staff, it is our understanding that the NRC has requested a response to the November 9,1979 Imc letter regarding information associated with fuel rod models used in the Farley LOCA/ECCS Model for Unit 2.

Since the original request, Westinghouse recognized a potential discrepancy in that the heatup rate dependence of burst was not properly considered. An evaluation of the impact of the heatup rate dependence on fuel rod burst was presented in letter NS-TMA-2163 dated November 16, 1979

"'he information provided in the attachment contains a response to the original request, improvement to the heatup rate prior to burst definition and the use of credit from improved analytical and modeling techniques to offset the effect of the new NRC model to meet the acceptance criteria for 10CFR50.h6 vith an FQ (heat flux hot channel factor) of 2.32.

Sheuld you have any questions, please advise.

Yours very truly, v g /) w: .

, L. -

' ll.L V.4 ?,

F.'L. Clayton, J:.

RWS:de O

Enclosure S

cc: Mr. R. A. Thomas Mr. G. F. Trowbridge //

Mr. L. L. Kintner 7 Mr. W. H. Bradford I 8006

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ATTACHMENT A. Evaluation of the potential impact of using fuel rod models presented in draft NUREG-0630 on the Loss of Coolant Accident (LOCA) analysis for Joseph M. Farley Unit 2 .

This evaluation is based on the limiting break LOCA analysis iden,tified as follows:

BREAK TYPE - DOUBLE ENDED COLD LEG GUILLOTINE BREAK DISCHARGE COEFFICIENT 0.4 WESTINGHOUSE ECCS EVALUATION MODEL VERSION Modified

• 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 Smal1~ Break, October 1975 Model". Fuel rod burst curves used in this analysis represented clad heatup rates of 10 Deg. F/sec for the Hot Rod and 10 Deg. F/sec for the Average Hot Assembly Rod.

CORE PEAKING FACTOR 2.32 HOT R0D MAXIMUM TEMPERATURE CALCULATED FOR THE BUPST REGION OF THE CLAD - 1974 0F = PCTg

,k ELEVATION - 6.0 Feet.

~

HOT ROD MAXIMUM TEMPERATURE CALCULATED FOR A HON-RUPTURED REGION OF THE CLAD - 2200 0 F = PCTN ELEVATI0M - 7.5 Feet CLAD STRAIN DURING BLOWDOWN AT THIS ELEVATION 0.9 Percent MAXIMUM CLAD STRAIN AT THIS ELEVATION 3.4 Percent Maximum temperature for this node occurs when the core reflood rate is less than 1.0 inch per second and reflood heat. transfer is based on the Steam Cooling calculation.

AVERAGE . HOT ASSEMBLY R0D BURST ELEVATION - 6.0 Feet HOT ASSEMBLY BLOCKAGE CALCULATED - 47.0 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 (Fo) required to maintain a peak clad tem-perature (PCT) of 22000F and in terms of a change in PCT at a constant FQ. Since the clad water reaction hte increases sig-nificantly at temperatures above 22000F, 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 wh!ch causes the PCT to remain in the neighborhpod of

'22000F justifies use of this evaluation procedure.

From NS-Tr%-2174:

For the Burst Ncde of the clad:

0.01 AFQ s 1500F BURST NODE APCT

- Use of the NRC burst model could recuire an FQ reduc, tion of 0.015 ,

The maximum estimated impact of using the NRC strain anodel- '

is a required FQ reduction of 0.03. -

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

=

APCT) (.015 + .03) (1500F/.01) = 6750F Margin to the 22000F limit is:

=

APCT2 22000F - PCTB = 2260F .

The FQ reduction required to maintain the 22000F clad temperature -

limit is: -

AFQB = (APCT1 - APCT 2 ) ( 50 F )

i = (675 - 226) ( 0)

= 0.03

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 poten-tial impact on that maximum clad temperature of using 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 increcse resulting from a change in strain (in the Hot Rod) is +200F per percent decrease in strain at the maximum clad temperature locations. ,

Since the clad strain calculated during the reac*wr coolant system i blowdown phase of the accident is not changed by the use of MRC fuel rod models, the maximum decrease in clad strain that must be considered here is the difference between the "caximum clad strain" and the )

" clad strain during blowdown" indicated above.

C. (

. Therefore:

APCT3* ( strain) (MAX STRAIN - BLOWDOWN STRAIN)

= .009)

( )) (.034

= 0F 50 The second aspect'of the analysis that can increase PCT is the flow blockage calculated. Since the greates value of blockage indicated by the NRC blockage model is 75 percen:, 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-Th%-2174.

Therefore: .

=

APCT4 1.250F (50 - PERCENT CURRENT BLOCKAGE)

+ 2.360F (75-50)

=

1.25 (50 - 47) + 2.36 (75-50) 0

= 63 F

If PCTN occurs when the core reflood node is greater than 1.0 inch per second APCTg = 0. The total potential PCT incrhase for the non-burst node is then APCTS = APCT3 + APCT4

= 50 + 63 = ll30F Margin to the 22000F limit ir APCT6

= 22000 F - APCTg = 0 The FQ reduction required to maintain this 22000F clad temperature limit is (from NS-TMA-2174).

AFQg = (APCT5-APCT)(iof 6 PCT I l

=

AFQ 3 0.11_ _

.- j The peaking factor reduction required to maintain the 22000F clad temperature limit is therefore the greater of AFQg and AFQg .

. l 1

or: A FQ PENALTY = 0.11

~B. The effect on LOCA analysis results of using improved analytical and  !

modeling technic 9es (which are currently approved for use in the l Upper Head Injection plant LOCA analyses) in the reactor coolant i system blowdown calculation.(SATAN computer code) has been quantified i 1

~

C (- .

.via an analysis which has recently been submitted to-the NRd for review. Recognizing that review of that analysis is not yet complete and that the benefits associated with these model improve- .

ments 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 respecti.vely.

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 A FQ calculated in Section (A) above (but not greater than zero R TY FQ ADJL!STMENT = 0.15 - 0.11

= 0 .

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