ML20054L859
| ML20054L859 | |
| Person / Time | |
|---|---|
| Site: | Big Rock Point File:Consumers Energy icon.png |
| Issue date: | 07/02/1982 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20054L857 | List: |
| References | |
| NUDOCS 8207090014 | |
| Download: ML20054L859 (5) | |
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w 4eny SAFETY EVALUATION REPORT BIG ROCK POINT PLANT _
SPENT FUEL POOL THERMAL-HYORAULIC ANALYSIS IN SUPPORT OF REQUEST FDR CONTINUED OPERATION Introduction 21,1982 (Reference 1) requested Consumers Power NRC letter dated May Company (CPC) to, " provide justification for continued operation of the facility considering that safety grade equipment is not available to In cool the pool and containment access could be limited by a LOCA."
support of their response to this request (Reference 2) Consumers Power Company has submitted thermal-hydraulic analyses which address heat-up of the pool following loss of normal cooling capability ahd the adequacy The review and of a newly installed auxiliary pool water make-up line.
evaluation of these analyses are the subject of this report.
Discussion (1) to show that sufficient time exists The purposes of the analyses are:
following losses of both normal cooling capability and containment access for remote manual initiation of auxiliary make-up cooling flow before pool temperatures reach 150*T; (2) and demonstrate that the maximum pool wa temperature can be maintained below 150*F by adding cool water through the new make-up line and discharging warmer water in the normal way by The limit of 150*F is the temperature above-overflow to a surge tank.
which the ACI-349 code requires testing to evaluate reductions in concrete Staff evaluation of the new auxiliary make-up flow delivery system strength.
is discussed in ASLB hearing testimony concerning spent fuel pool modi 8207090014 820702 PDR ADOCK 05000155 P
The licensee's analyses are based on hand calculations of the bulk water temperature in the pool.
The detemination of pool heat load considered the actual operating history and time since discharge of each of the 132 fuel assemblies presently in the pool. All discharges up to, and including that from the 1982 refueling outage were considered. The calculation of decay heat load was based on ANS Standard (ANSI /ANS-5.1-1979) on decay power in light water reactors. The heat load input to the calculations is.046 mwt.
The heat-up of the pool water was assumed to be adiabatic (i.e., no heat transfer from or to surroundings). Make-up water can be delivered by the core spray pumps at a minimum flow rate of 13 gpm. The make-up water temperature was assumed to be 100 F.
The initial pool water temperature was assumed to be 100*F. The general practice of operating the pool below 100*F was sighted as the basis for this latter assumption. Mixing induced by density gradients was assumed to t;e sufficient,to maintain a uniform temperature throughout the pool. The licensee's calculations show that:
(1) in the absence of any cooling it will take more than eight (8) days to raise the bulk pool water temperature from 100*F to 150*; (2) with make-up water cooling the bulk pool temperature will be maintained at less than 125 F.
Evaluation Spent Fuel Decay Heat Load Detailed calcul'ations of the spent fuel decay heat load were provided 'by the licensee. They have been' reviewed and found acceptable.
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Make-Up Water Flow Rate and Temperature The make-up water system design has been reviewed and approved by the-staff. Bases for make-up water flow rates have been presented by the licensee in ASLB hearings.
In discussions with the 1,icensee, staff concern was raised over the close proximity of the make-up line injection location to the pool overflow discharge wall. Specifically, if the momentum of fluid being discharged is significantly larger than that of the injected fluid, significant amounts of injected fluid may be immediately discharged without removing any heat from.ihe pool.
Irt discussion on this question the licensee has stated that they considered this problem qualita-tively and felt significant discharge of incoming coolant would not occur.
Staff estimates of the injection fluid velocity (5 ft./sec.) support this conclusion.
The assumed temperature of the pool make-up water,100*F, is consistent with the exit temperature of the core spray heat exchanger.
Assumption of perfect Mixing In discussions with the licensee the assumption of perfect mixing was questioned (i.e., bulk fluid temperature represents max. fluid temperature).
The licensee presented qualitative arguments to support their assumption and referenced three-dimensional calculations of thermal-hydraulic conditions i
in the pool peiiormed by NUS Corporation.
These calculations indicate a fairly uniform temperature distribution within the pool for temperatures near boiling and no make-up water injection. The largest calculated temperature difference within the pool is,about 10 F.
Therefore, the staff.
feels that a 10*F temperature difference between maximum pool temperature and bulk pool temperature should be assumed in the subject analyses.
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4-Boundary and Initial Conditions The initial pool temperature is assumed to be at the normal pool operating temperature of 100 F.
Although their are no requirements on pool operating temperatures, the staff feels this assumption,is reason-able and acceptable.
Heat-up of the pool is assumed to be adiabatic. The licensee states
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that this is a conservative assumption since the calculated pool temperature' will be larger when heat loss to the environment is neglected. In a normal
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containment environment this is clearly the case.
For a post-accident environment the degree of conservatism, if any, is not obvious.
In considering the appropriateness of this assumption for a post-accident environment, she staff raised the issue of spent fuel p,ool heat-up via energy released to containment structures during the LOCA accident. In response to this concern the licensee referred to containment analysis presented in their Hazards Summary Report, which shows that containment air temperature remains above 150*F for only a few hours following a LOCA accident.
Recent preliminary SEP containment temperature calculations r-for the Big Rock Point plant (Reference 3) indicate that the time above 150 may be as long as 1 day. Staff estimates of heat-up time constants l
for 6 foot and 3.5 foot concrete slabs are 12 day and 4 day respectively.
i Based on these data the staff feels that exposure of the SFP concrete walls to an atmosphere above 150 F for the longer period of 1 day would not result in bulk concrete temperatures exceeding 150 F.
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Conclusions The staff concludes that the licensee's fuel pool heat-up analysis is basically sound, but should account for a 10 F temperature difference between maximum fluid temperature and bulk fluid temperaturq..Thus, we conclude that it would take nore than 6.4 days (40/50 X 8) for the temperature of the SFP water to reach 150*F; and with make-up water cooling the maximum SFP fluid temperature will be kept below 150*F.
Based on review of containment temperature analysis and estimates of
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heat-up time constants for concrete slabs', we conclude that containment temperatures in excess of 150*F for less than one day will not result in bulk concrete temperatures above 150*F.
This safety evaluation was prepared by M. Caruso, Systems Section, Operating Reactors Assessment Branch, Division of Licensing.
References 1.
NRC letter, G.C. Lainas (NRC) to David M. VanderWalle (CPC),
Subject:
Spent Fuel Pool Structural Adequacy - Big Rock Point, dated May 21, 1982.
2.
CPC letter, David J. VanderWalle (CPC) to Gus C. Lainas (NRC),
Subject:
Big Rock Point Plant - Spent Fuel Pool Structural Adequacy, dated June 4, 1982.
3.
Er.losure to NRC letter LS05-82-06-027, D.M. Crutchfield, (NRC) to D.J. VanderWalle (CPC), Systematic Evaluation Program (SEP) for the Big Rock Point Plant - Evaluation ' Report on Topics VI-2.D and VI-3, June 10,1982.
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