ML17333B004

Responses to RAI on Holtec Rept HI-951389 DC Cook Spent Fuel Pool.

ML17333B004
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Site:	Cook
Issue date:	08/14/1997
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HI-971763, NUDOCS 9708250095
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IS%58 HOLTEC Hdltec Center, 555 Lincoln Drive West. IVlarfton NJ 08 "53 Telephone (609) 797- 0900 Fax (609) 797 - 0909 I N T E R N A T I 0 N A L REVIEW AND CER7IHCATlON LOG DOCUMENT MAME:- Responses to RAI on Holtec Report HI-951389 forthe O.C. Cook Spent Fuel Pool HOLTEC DOCUMENT I.D. NUMBER: 971763 70851 HOLTEC PROJECT NUMBER:

CUSTOMER/CUENT: American Electri Power RFVlSION BLOCK X

REVISION AUTHOR & REVIEWER & APPROVED& DIST.

NUMBER 'ATE DATE DATE ORIGINAL tNbREyyg &P~ Sv z %Ger

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it-(97 REVISION I REVISION 2 REVISION 3 REVISION 4 REVISION 5 REVISION 6 This document conforms to the requirements of the design specification and the applicable sections of the governing codes.

Note: Signatures and printed names required in the review block.

A revhion of this document will be ordered by the Project Manager and carried out ifany of its contents is materially affected during evolution of this project. The determination as to the need for revision will be made by the Project Manager with input from others, as deemed necessary by him.

Must be Project Manager or his designee.

x Distribution: C: Client M: Designated Manufacturer F: Florida Office Report categoly on the cover page indicates the contractual status of this document as A = to be submitted to client for approval I = for client's information N = not submitted externally THE REVISION CONTROL OF THIS DOCUMENT IS BY A

SUMMARY

OF REVISIONS LOS" PLACED BEFORE THE TEXT OF THE REPORT.

97G825GG95 97G8<9 POR AOQCK GSGGGM5 P POa

SUMMARY

OF REVISIONS REVISION 0: This revision contain the following sections and pages.

Title Page Review and CertiGcation Log Summary ofRevision Log Table of Contents Figures Appendix A Appendix 8* 14

~ Note: This appendix contains Holtec proprietary information, is therefore not distributed. This appendix is available for review at Holtec's corporate ofices.

Holtec Report HX-971763 Holtec Project 70851'

K,Nil I;0.

'l Xntro duction TABMOF CONTENTS

~ae 2.0 AEP Request - Description of Analysis Methods 3.0 NRC Request I 4.0 NRC Request 2 5.0 NRC Request 3 6.0 References Tables Figures Appendix A Proprietary Appendix B~

'ote: This appendix contains Holtec proprietary information, is therefore rot distributed. This appendix is available for review at Holtec's corporate offices.

Holtec Report HI-9? 1763 Holtec Project 70851

1.0 INTRODVCTION This report documents analyses performed. in support of American Electric Power (AEP) personnel responding to a USNRC'Request.for Additional Information (RA@ on the thennal-hydrauEcanaIysis of theCook Nuclear Plant'spent fuel "pool. (SFP) P}; This report addresses the use ofthe Unit 2 uprated reactor power in decay heat calculations.

Sections 2.0 through 5.0 each contain the response to an individual NRC or ABP question.

Where appropriate, references to and comparisons with the result of the previous analyses [1} are performed. Not all of these four sections contain analyses.

Holtec Report HI-971763 page 1 Holtec Project 70851

2.0 AEP REQUEST - DESCRIPTION OF ANALYSISMETHODS 2.1'ecay Heat Analysis Method All;decay heat calculations. are performed using implementations.of the-OIUGB52 [2J computer code developed at Oak Ridge National Laboratory. This program has a long history of use in the commercial nuclear power industry for both isotope production and thermal power calculations.

The OMGEN2 code is a rigorous isotope generation and depletion code which accurately predicts the products and by-products of Qssion and the resulting heat generation rates.

The decay heat generation rate in the pool consists of two components: the decay heat generated by previously discharged fuel assemblies and the decay heat generated by &eshly (recently) discharged assemblies. The decay heat contribution of previously discharged fuel assemblies changes very little over short periods of time, and is therefore held constant in the analyses.

Because of the nature of exponential decay, this simplification is conservative. The Holtec QA Validated LONGOR [3] computer proem, which incorporates the ORIGEN2 code, is used to calculate this decay heat component.

The decay heat contribution of the freshly discharged 'fuel assemblies changes substantially over even very short periods of tune. 'I'his decay heat contribution is therefore evaluated as time>>

varying. The Holtec QA Validated BULKTEM [4] computer pro~~ which incorporates the ORIGEN2 code, is used to calculate this decay heat component.

2.2 Bulk SFP Temperature Analysis Method Due to the time-varying decay heat component, the total decay heat is also time-varying. The bulk SFP temperature is therefore'calculated as a function of time. The following energy balance is solved to obtain the temperature at each instant in time:

C = Q ( )-0 ('1)-0 (T) where:

C is the SFP thermal capacity, Btu/'F T is the bulk SFP temperature, 'F z is the time after reactor shutdown, hr Qc+w) is the decay heat generation, Btu/hr QHx(T) is the SFPCS heat rejection, Btu/hr

~Ap(T) is the evaporative'heat,loss, Btu/hr The evaporative heat loss term includes both evaporative and sensible heat transfer from the surface of the SFP. The implementation of this term has been benchmarked against actual in-plant test data [5]. The solution of this first-order ordinary differential equation is performed using the BULKTEM pro~ [43 Holtec Report HI-971763 page 2 Holtec Project 70851

Tune-to-Boil Analysis Method I:o11owing a loss of forced cooling, the continuing decay heat load in the SFP will cause the bulk SFP temperature to use. The equatioa energy balance. which defines this transient phenomena is sitmhr to the.ODE.presented in Section 22, but does not include the.QRz term and does include a time varying SFP thermal capacity, to account for the evaporative water losses. The time available for corrective action before bulk SFP boiling occurs is determined using the Holtec QA Validated TBOIL computer program [6].

The decay heat generation and evaporative heat loss terms in this formulation are identical to those defined in Section 2.2, except for the following two differences:

o The decay heat is calculated using the correlations of USNRC Branch Technical Position ASB 9-2 I'7] instead of ORIGEH2.

~ No incremental credit is yven for evaporative heat loss at SFP bulk temperatures greater than 170'F.

2.4 Local Temperatures Analysis Method

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The decay heat generated by the fuel assemblies stored in the SFP induced a buoyancy driven flow Geld upward through the fuel rack ceHs. Cooler water is supplied to the bottom of the racks cells through the rack-to-wa)l gaps and rack-to-floor plenum.

A computational method for modeling this phenomena is given by Sin~~ et al. I'8). The method presented in the reference has been incorporated into the Holtec QA Validated computer pro~

THERPOOL [9), this is used to perform this analysis.

Holtec Report HI-971763 page 3 Holtec Project 70851

3.0 NRC REQUEST 1 "With regard to the spent fuel pool (SFP) cooling analyses for the normal refueling scenarios, Case lA and 2'as presented in February 1, 1996 submitta1 are based on the spent &el assunblies dischar ed Gom Unit.1 during Cycle.25A Since Unit 2.

will be operating at a higher power level than Unit 1 (3588 MWt vs 3250 MVt),

the analyses for Case IA and 2 should be revised based on the spent fuel assemblies discharged trom the Unit 2 reactor during Cycle 20B. Also, Tables 3, 4 and 5, and Figures I, 3, 6 and 8 should be revised to include the results from the above revised analyses."

In addition to the difference in reactor thermal power between Unit 1 and Unit 2, there are differences in the maximum burnup, initial U~q enrichment and &el assembly uranium weight.

These, differences are summarized in the Table 1. All of the values in Table I are extracted from Reference 1.

As requested, the cases designated as IA and 2 are re-evaluated using the Unit 2 values for the four parameters presented in Table I. All input values are taken from Reference I, and all inputs except those presented in Table 1 are identical to those used in the reference work. Unlike the oriynal .calculations, however, the thermal transient evaluations performed in ths report utilize version 3.0 of the BULKTEM program tl I]. This newer version of the BULKTEM code contains modification to the evaporative loss correlations [12], which are slightly more accurate than the original correlations, The effects of this modification on the results of the analysis are minimal.

The results of the maximum SFP bulk temperature analyses are presented in Table 2, where they are also compared with the previously reported values (I]. Temperature profiles for each case are presented in Figures 1 and 2. Net decay heat load and evaporative heat loss pro6les for each case are presented in Figures 3 and 4. As expected, the maximum bulk SFP temperatures are marginally higher than previously reported.

The results of the bulk temperature analysis are propagated through to the time-to-boil and local temperature analyses, the results of which are presented and compared with the corresponding previously reported values [I] in Tables 3 and 4, respectively. As expected, the minimum time-to-boil is slimly less than previously reported, and the maximum evaporation rate and local temperatures are slightly higher than previously reported.

Holtec Report HX-971763 page 4 Holtec Project 70851

4.0 NRC REQUEST 2 "In.the analyses for the scenario of back-to-back Rll core discharge with two SFF trains (Case,3),"'pent fuel assembEes Rom Unit 2;are assutned,to be 'ooling discharged m three:groups'each with. a diQerent burnup:vaIue= Provide curves to show the decay heat rates as a function of time generated in the SFP Rom each of these youps."

Figure S presents the decay heat profiles for each of the three groups of the Rll core discharge batch for Case 3. As expected, the decay heat generation rate and the reactor exposure are directly proportional.

Holtec Report HI-971763 page 5 Holtec Project 70851

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5.0 NRC REQUEST 3 "In the response (A 4) to the staQ's RAX presented in Pebtuary 1,'1996 submittal, decay heat generation rates for spent fuel assemblies Rom each previous discharge cycle are provided Decay heat generation rates Rom. these previously discharged spent fuel assemblies are also provided in the Attachments 2 and 3 to the letter dated August 1, 1996. However, decay heat generation rates presented in August 1, 1996 submittal deviate significantly Rom that presented in Pebruaty 1, 1996 submittal. Provide clarification and justification for this discrepancy."

The February 1, 1996 submittal is in response to an NRC RAI on Holtec Report HI-941183. The August 1, 1996 submittal is in response to an NRC RAI on Holtec Report HI-951389. A discussion of these diQ'erences between these decay heat generation rates has previously been provided in response I.C of the August 1, 1996 submittal [10].

Holtec Report HI-971763 page 6 Holtec Project 70851

6.0 REFEIU2lCES

[1] "Updated Thermal-Hydraulic Analysis of Spent Nuclear Fuel Pool,.- Donald C. Cook Nuclear Plant" Holtec Report HI-951389, Revision'.-

[2] A.G. CrofE "ORNL Isotope Generation and Depletion, A User's Manual for the ORIGEN2 Computer Code," ORNL/TM-7175, RSIC/CCC-371, Oak Ridge National Laboratory, July 1980.

[3] "QA Documentation for LONGOR v1.0," Holtec Report HI-951390, Revision 0.

[4] "QA Documentation for BULKTEMv2.0," Holtec Report HI-951391, Revision 0.

[5] Wang, Yu, "Heat Loss to the Ambient trom Spent Fuel Pool: Correlation of Theory with Experiments," Holtec Report HI-90477.

[6] "QA Documentation for TBOIL v1.6," Holtec Report HI-92832, Revision 2.

[7] USNRC Branch Technical Position ASB 9-2, "Residual Decay Energy for Linet Water Reactors for Long Term Coolino Revision 2, July 1981.

[8] Sin+~, K.P. et. al., 'Method for Computing the Maximum Water Temperature in a Fuel Pool Containing Spent Nuclear Fuel", Heat Transfer Engineering, Volume 7, Number 1-2, pp. 72-82, 1986.

[9] "QA Validation for THERPOOL v 1.2", Holtec Report HI-87120, Revision 2.

[10] Letter Gom E.E. Fitzpatrick (AEP) to USNRC, Docket Numbers 50-315 and 50-316, Document ID AEP:i&C.C:1202B, Attachment 1, Response 1.C.

fl 1] "QA Documentation for BULKTEMv3.0", Holtec Report Hl-951391, Revision 1.

[12] "An Improved Correlation for Evaporation from Spent Fuel Pools," Holtec Report HI-971664, Revision 0.

Holtec Report HI-971763 page 7 Holtec Project 70851

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TABLE 1 DIFFERENCES BEWVEEN UNIT I AND UNIT 2 NORMALDISCHARGES Parameter Unit I Value Qmt 2 Valee Reactor Thermal Power (MVt) 3,250 3,588 Maximum Average Burnup (MWdMTU) 52,200 68,400 Initial U~ Enrichment (%) 3.50 4.00 Assembly Uranium Weight (kg) 461 410 Holtec Report H1-971763 Holtec Project 70851

TABLE 2 RESULTS OF MAXIMUMBULKSPP TEMPERATURE ANALYSES Parameter Current Results (Unit 2) Previous Results (Unit 1)

Case IA Magnum SFP Temperature 156.56'F 154 37'F Coincident Time After Shutdown 138.0 hrs 138.0 hrs Coincident Net Heat Load to HXs 28.50x10 Btu/hr 27.19xl0 Btu/hr Coincident Evaporative Heat Loss 2.79x10 Btu/hr 2.35x10 Btu/hr Case 2 Maximum SFP Temperature 129.84'F 128.68oF Coincident Time After Shutdown 130.0 hrs 131.0 hrs Coincident Net Heat Load to HXs 30.75x10 Btu/hr 29.32x10 Btu/hr Coincident Evaporative Heat Loss 0.99xlO Btu/hr 0.57xl0 Btu/hr Holtec Report HI-971763 Holtec Project 70851

TABLK3 RESULTS OF BOILINGTMFS ANALYSES Parameter Current Results (Unit 2) Previous Results (Unit I)

Case lA Time to Start of Boiling 8.53 hrs 9AS hrs Maximum Evaporation Rate 66.83 gpm 63.35 gpm Case 2 Time to Start of Boiling 12.11 hrs 13.37 hrs Maximum Evaporation Rate 67.30 gpm 63.64 gpm Holtec Report HI-971763 Hol tee Project 70851

TABLE 4 RESULTS OF MAXIMUMLOCALTEMPERATURES ANALYSIS (Case.IA Only)

Parameter Current Results (Unit 2) Previous Results (Unit 1)

No Blocka~e Maximum Local Water Temperature 166 O' 163.6'P Maximum Fuel Clad Temperature 216.3'P 214.5'P 50% Blocha e Maximum Local Water Temperature 226. lop 223 5'F Maximum Fuel Clad Temperature 256.8'P 254 3oP Holtec Report HI-971763 Holtec Project 70851

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FlGURE 1: Spent Fuel Pool Bulk Wateg Temperature Profiles Case 1A, Normal Discharge, 1 Cooling Train .

160 155 150 0

" 1<5 E

~ 140 63 135-130 0 50 100 150 200 250 300 350 400 450 500 Time After Reactor Shutdown (hrs)

Hoitec Report Hl-971763 Holtec ProJect 70851

F fGURE 2: Spent Fuel Pool Bulk Water Temperature Profiles Case 2, Normal Discharge, 2 Cooling Trains 130 C

128 126 LL 124 Q 122 L

~~ 120 Ql 118 116 114 50 100 150 . 200 250 300 350 400 450 500 Time After Reactor Shutdown (hrs)

Holtec Report Hi-971763 Holteo pro/cot 70851

FIGURE 3: Spent Fuel Pool Decay Heat Load and Loss Profiles Case 1A, Normal Discharge, 1 Cooling Train 35.0E46 30.0E+6 Net Decay Heat Load 25.0E46 .-

M 4I Vl 0

C 20.0E+6 x'aCl C

cf

'0 tl$

O '15.0E+6 C$

x C 10.0E46 Q

n 5.0E+6 Evaporative Heat Loss 000.0E+0 50 100 150 200 250 300 350 400 450 500 Time After Reactor Shutdown (hrs)

Holtec Report Hl-9?1763 Holtec Project 70851

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FIGURE 4: Spent Fuel Pool Decay Heat Load and Loss Profiles Case 2, Normal Discharge, 2 Cooling Trains 35.0E46 30.0E+B Net Decay Heat Load 3

25.0E+6 ~ ~

g 20.0E+6 '

o 15.0E+B 5 10.0E4B A

z 5.0E+B-Evapora(ive Heat Loss 000.0E40 50 100 150 200 250 300 350 400 500 Time After Reactor Shutdown (hrs)

Hoitec Report Ht-971763 Hottec ProJect,70851

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FIGURE 6: Decay Heat Generation Rate for Each Discharge Batch ln the Full Core Back-to-Back Discharge Case 3 15.0E+6 Three Exposure Cycles 14.0E+6 Two Exposure Cycles 13.0E+6 Pg 12.0Et6 PL c 11.0E+6 One Exposure Cycle 10.0E+6 6

9.0E+6 n

8.0E+6 .

7.0E<6 6.0E+6 50 100 150 200 250 300 350 400 450 500 Tlrne After Second Reactor Shutdown (hrs)

Holtec Report Hl-971763 Holtec Project 70851

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ATTACHMENT 2 TO AEP:NRC:1202D RESPONSE TO QUESTION 4 REQUEST FOR ADDITlONAL INFORMATION REGARDING REFUELING OPERATIONS DECAY TIME to AEP:NRC:1202D Page 1 NRC uestion 4.0 "Is full-core offload a current practice during normal refueling?"

Res onse to uestion 4.0 Current practice is to perform full core offloads.