ML20132A862

Assessment of Effect of Increased Fuel Rod Fill Gas Pressure on Core 14 ECCS Performance Analysis

ML20132A862
Person / Time
Site:	Yankee Rowe
Issue date:	08/21/1979
From:	YANKEE ATOMIC ELECTRIC CO.
To:
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ML19347A562	List: ML20132A862
References
NUDOCS 7908240463
Download: ML20132A862 (8)

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ATTACHNENT A 1

Assessment of the Effect of Increased Fuel Rod Fill Cas Pressure

. ca Core XIV ECCS Performance Analysis <

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August 1979 upf'"W"!!

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Table of Contents ,

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. Introduction ,

2.0 Effect of Increased Fuel Rod Fill Cas' Pressure on Small Break LOCA 3.0 Effect of Increased Fuel Rod Fill Cas Pressure on Large Break LOCA 3.1 General Comments 3.2 Break Spectrum Analysis 3.3 Burnup sensitivity Analysis 3.4 Effect of Increased Fuel Rod Fill Cas Pressure on Large Break LOCA Calculations 4.0 Summary and Conclusions 1

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1.0 Introduction During recent work performed by our fuel supplier, it was discovered that the initial fill gas pressure of the fresh fuel loaded into Core XIV was higher than the design specification of 125 5 2 psia. The maximum increase in ,,

the fill gas pressure was determined to be 18 psi with the mean increase being 13.4 psi. '

j Since the nominsi initial fuel rod illi gas pressure is input to the ECCS J Performance Analysis, an assessment of the effect which the higher i pre pressurination level has on large and small break LOCA analysis has been

, made. Only the fresh fuel loaded into Core XIV is affected.

l 2.0 Effect of Increased Fuel Rod Fill Cas Pressure on Small Break Loss of i Coolant Accident Analysis

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l References 1 and 2 provided a complete small break LOCA analysis for j Yankee Rowe Core XIII, the reference cycle. The small break results are

characterized by relatively low peak clad temperature with respect to Appendix j K limits and relatively high system pressure with respect to large break J

LOCA. The most limiting small break was the 4.0 inch ID cold leg break which had a PCT of 1793.4 0F. The effect of the increased fuel rod fill gas

pressure on the small break LOCA results would be to reduce the predicted j PCT's due to the better gay conductance caused by the higher heluia content.

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! Fuel rod balloning and rupture would not occur with the higher fill gas j pressure since the temperatures predicted are low while the system pressures are high. Thus, the small break results presented in References 1 and 2 i remain valid.

• 3.0 Effect of Increased Fuel Rod Fill Cas Pressure in Large Brer.k LOCA -

I 3.1 Ceneral i References 1 through 9 provided a complete Loss of Coolant Accident Analysis for Yankee Rove Core XIII operation and serves as the reference i analysis for the current cycle (Core XIV). Section 7.12.3 of Reference j 10 provides the results of a burnup sensitivity study for Core XIV i utilizing the same analytical techniques employed in the Core XIII l reference analysis. The following discussion briefly describes our large break LOCA analysis and burnup sensitivty study methodology and then

details the effect the increased fuel rod fill pressure has on the large

{ break LOCA results submitted for the current cple (Reference 10).

f l 3.2 Break Spectrum Analysis

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In accordance with 10CFR50.46 Appendix K, a large break spectrtsa analysis has been performed and submitted as previously mentioned for Yankee Rove Core XIII utilizing Yankee Atomic's k' REM-Based Generic Pk'R l ECC Evaluation Model. This model is basically comprised of the

} RELAP4/ MOD 3 blowdown, hot channel and reflood models, the T00DEE-2EM fuel i

i '. y rod heatup code and the CAPEX fuel tod performance code. Peak clad temperatures are calculated for guillotine and slot type break sizes with discharge coefficient ranging from 1.0 to 0.6 (or 0.4).

• Beginning-of-life core conditions are asssssed since the maximum fuel rod stored energy as predicted by the CAPEI code occurs at this time due to the significant pellet to clad gap.

The break spectrina analysis is performed with the hot rod power level consistent with meeting Appendiit K limits. Thus, a peak linear heat generation rate (LHCR) for fresh fuel of 9.70 kv/f t was obtained for the reference cycle with the 1.0 DECLC break size and type being most limiting.

3.3 Burnup Sensitivity Analysis At % .fyde, the fresh f=1 is 1Mting ene to the significant pellet to clad gap and resultant high stored energy. During the first fee asys of espesure, the fresh feel peIIec to clad Emp u6t$1 a - ---_ " _ h Ern M enuc33 Thus ,Afr.is possible to increase the peak IBGE such that the criteria set farth in Ayyandfx E a:= sciII mac aEmsg =Frik -nfesEng ma EHER ene per:mics SrH games: gZme ag='-M-Esmuser, as eSe cycle peugn=====, the final zud peIIec to cIaf guy as langer changes as it did in the first few days and fismiam 3,ss cant in===

to be released, degrating the gay heat transfer coefficient an5 increasing the feel red pr====ce. See to the r=1meh ely Iang refi21 period and low fuel rod fill gas pressure, rod rupture cannat analytically be tolerated since it uoold occur at an elevated temperature

=A== the 2r-02 reaction is higbly +=nehermic. Thus, the effect of the

, above mentioned fuel rod burnup dependent changes on peak LECR are addressed at various cycle average burnup conditions (BOC, 337 MWD /M, 840 MED/M, 6000 MMD/m and 16000 MED/m). Utilizing the blevdown results of the most limiting break size (1.0 DECLC) fuel rod heatup calculations are performed at the above burnup p:c.ints. A curve of allevable peak rod LEGR versus cycle burnup is then generated for incorporation into plant technical specifications.

3.4 Effect of Increased Initial Fuel Rod Fill Cas Pressure on Large Break ECCS Performance Calculation ,

The increased initial fuel rod fill gas pressure results in two competing effects on ECCS performance analysis calculations which diminish with increasing fuel rod exposure. At beginning of cycle the peak fresh fuel rod has more helitas in it than the design situation which results in a slightly better pellet-clad gap heat transfer coefficient (h ,p) and a somewhat lower stored energy. This improvedgh , also alfows more energy to be removed in the heatup calculations than in the design case and hence would result in a slightly lower PCT. However, due to the restriction that pre.clusion of rod rupture presents for Yankee Rowe fuel in ECCS licensing calculations, the hir.her fuel rod fill pressure may result in clad balloning and rupturo at a temperature where zirconium water reaction rates are highly exothermic. As the fuel rod exposure increases, the effect of the increased fill pressure diminishes since the firsion gas released into the gap and plenum becomes dominating.

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- 1 In order to determinst the sensitivity associated with the increased )

fuel rod fill gas pressurn, the bot rod calculations supp'orting the fresh fuel allouable rod LEGE versus Core IIY bornup curve (Tech. Spec. Figure 3.2.1) were reanalyzed with an initial fill gas pressure of 143 psig.

This pressure reflects the highest observed fill pressure increase.

Table 1 compares the result of the re-analysis at the previously i mentioned burnup points for Core XIV.,

The predicted clad temperatures for Core IIV at BOC, 6000 MWD /MIU and 16000 MWD /M given is Table 1 for the case of increased fuel rod fill pressure are slightly louer than the respective design cases. With

he increased fill gas pressure, only at the 337 MWD /MIU and 840 MED/MIU burnup points did rupture occur with the original peak LEGR's of 11.5 kw/ft and 12.0 kv/ft. In order to achieve acceptable results, the peak LHCR's at these points were reduced in power by 2.52.

4.0 Sissaary and Conclusions The peak rod LEGR's reported previously in Technical Specification Figure 3.2.1 for TE Core IIT for 0 MWD /MIU, 6000 MWD /MIU and 16000 MWD /MIU burnup remain valid with the increased fuel rod fill pressure. Only the points at 337 MWD /MIU and 840 MWD /NIU burnup had to be slightly reduced in power to account for the effect of increased fuel rod till pressure.

Since the 337 MWD /MID and 840 MWD /MIU burnup points had to be reduced in pouer to meet licensing criteria with increased fill gas pressure, the operating history of Core IIV has been reviewed to determine if measured fresh fuel peak rod LEGR's had exceeded the revised fresh fuel allowable peak rod LHCR's given in Figure 1. Curve 1 on Figure 1 presents the original fresh fuel allowable peak rod LHCR versus burnup submitted for Core XIV. Curve 2 on

• Figure 1 represents the revised curve while Curve 4 shows the actual measured peak rod IJiGR's for Core XIV to date. Curve 3 on Figure 1 represents the peak rod LHCR required be full power. By comparing curve 4 to Curves 1 and 2, it is seen that at ao time during the current cycle had the LOCA linits been exceeded even '.; hough the fresh fuel allowable rod LHGR's in Curve 1 had to be reduced to Csrve 2 to account for the effect of increased fuel red fill gas pressure. 'thus, Core XIV operation to date has been conducted within the limits put forth in 10CFR50.46 Appendix K.

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• . t REFERENCES

1. Proposed Change No.145, Supplement No. 5, Yankee Rowe Core XIII ECCS Perfornance Evaluation, August 1,1977.

2. Proposed Change No.145, Supplement N'o. 7, WYR77-90, Additional Yankee Rowe Core X111 Small Break LOCA Analysis, September 21, 1977.

3. Proposed Change No.145, Supplement No. 5 Errata, Yankee Rowe ECCS Modifications, August 5,1977.

4. Yankee Rove Core XIII LOCA Analysis, WYR77-81, August 9,1977.

5. Yankee Rowe ECCS Modification, WTR77-81, August 22, 1977.

6. Proposed Change No.145 Supplement No. 6, WYR77-85, Yankee Rowe Core 13 Technical Specifiction/ECCS Accumulator, September 8,1977.

7. W. P. Johnson to USNRC, Yankee Rove Core XIII LOCA Core Inlet Tenperature and Acctznulator Delay Sensitivity Analysis, October 7,1977.

8. R. H. Croce to USN2C, Yankee Rove Core XIII LOCA Core Inlet Temperature and Acessaulator Delay Sensitivity Analysis Errata.

9. Proposed Change No.145 Supplement No. 8, WYR77-100, Yanke.e Rowe Core XIII LOCA Burnup Sensitivity Analysis Results, October 27, 1977.

10. YAEC-1162 Yankee Nuclear Power Station Core XIV Performance Analysis, -

September 1978.

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1 I TABLE 1 j

SUMMARY

OF RESUl.T8 .

EFFECT OF INCREASED FILL CAS PRESSURE ON YR 09E XIV IACA-BURNUP ANALYSIS

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i Core XIV 6000.0 16000.0 0.0 337.0 840.0

. Burnup (MWD /NTU)

Peak Rod LHCR (kw/f t) 9.44 11.19 10.91 11.68 11.38 11.0 9.73 i*

Initial Fuct Rod 143 125 143 125 143 125 143 1 Fill Cas Pressure 125 143 12S

! i (psis) i Fuel Pin Cas Inventory 3.59 4.04 3.61 4.06 3.65 4.10 4.0 4.46 4.59 5.04 3

(Cram-Mo en x 10 )

I i Peak Clad -

1895 1886 2123 l 2074 2198 2126 2037 2011 1840 1823 Temperture l (OF) i j

Time of PCT 140 153 151 182 172 196 182 188 188 (see) 144 1  !

! NO NO NO NO NO NO NO NO NO NO i '

Rupture _

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YANKEE-ROWE e Cf1Rt. XIV III.LOWOULC l'EHK ROD LHOR ' VERSUS CYCLE' UURNUP

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fi 3 P.) TEr.II. LPEC FOR FREnti FUEL ALLOWA6LE PCAK R00 LHOR v .

l,T,  !._ 2 O P.LVILLO fl.CH OPEC HITH INCREADED flN PREGOURE is

'_' $ 4_ 36 rEnn C00 tHGR REQUIRE 0 fOR FULL POWER n1 *

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b r---l0- - , 7 Ci il 13 . II .12 . I S . ~1 }4- r- 31 13 (i l' CORE XIV CYCLE AVERAGE BURNUP (1000 NWD/NTU1 Fir,urc !

Comparison Frcsh Fuel Allowable Peak Rod I.IIGR's to Actual Monsured Peak Rod I.llGR'n

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