ML18219E089

Response to Letter of 12/3/1975, Provide Requested Information Re Switchover from Injection to Recirculation & Procedures Permitting Diversion of Flow from Low Head Pumps to Containment Spray System

ML18219E089
Person / Time
Site:	Cook
Issue date:	12/23/1975
From:	Tillinghast J Indiana Michigan Power Co, (Formerly Indiana & Michigan Power Co)
To:	Rusche B Office of Nuclear Reactor Regulation
References
Download: ML18219E089 (16)

Text

fdRC D RIBUTION FOR PART 50 DQCKE'. ATERIAL (TEMPORARY FORM)

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FILE FRQM: indiana & Michigan Pwr C DATE QF DQC DATE R EC'D LTR TWX RPT OTHER New York, NY 12-23-75 12-30-75 XXX TO: ORIG CC OTHER SENT RRC PDR~g Mr Rusche one signed SENT LOCAL PDR CLASS UNCLASS PROPINFO INPUT NO CYS REC'D DOCKET NO:

XXXXXXXX 1 50-315 DESCR IPTION: ENCLOSURES:

r Ltr,re Qtr the following Addi info concerning switchover from jeig$ $ 7$ .

gag injection to recirculation' procedures "perITiitting diversion of flow from .the e

low head pum'ps 'to the containment spray

[rACKNOWLL~'DBED systems..... e PLANT NAME: D C Cook i/i'I.

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~ECULPTOPy DO-I;~T FII E ]O INDIANA R MICHIGAN POWER COMPANY P. O. BOX 18 BOWLING GREEN STATION NEW YORK, N. Y. 10004 D gerber 1975 Donald C. Cook Nuclear Plant, Unit 1 Docket No. 50-315 Oz DPR No. 58 OEG ~ > ~F6 CSG

%At Mr. Benard Rusche, Director u' > ~ucl~hc5+

co Office of Nuclear Reactor Regulation Xoj +i g U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Dear Mr. Rusche:

This letter, including attachments, responds to of December 3, 1975 requesting additional information your'letter regarding the switchover from injection to recirculation permitting diversion of flow from the low head pumps and'rocedures to the containment spray system.

Specific responses attached demonstrate that adequate time is available to perform the switchover from injection to recirculation. This time is based upon a simulated performance of a switchover to determine operator response time, equipment response times determined during preoperational testing, and the st'eps required for a switchover as described in Attachment A.

Regarding your second question on flow diversion, conservative analyses have been performed to determine the time that diversion to containment sprays is required. The time is based upon assumptions in Appendix N, Questions 0.3.1, Case A to the Donald C. Cook Nuclear Plant Final Safety Analysis Report.

In conjunction with the above responses, several changes to the operating procedures and setpoints have been made, as discussed in Attachment B.

Very truly yours, J n xl n s JT o malll Vice President Attachment cc: R. S. Hunter P. W. Steketee R. W. Jurgensen - Bridgman R. Walsh R. C. Callen R. J. Vollen G. Charnoff

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'Response to NRC Questions from December 3,, 1975 Letter NRC uestion 1 Demonstrate that adequate time is available to perform the switchover from injection to recirculation.

a) Provide the time required to realign the valves and pumps, including personnel response time, valve actuation times, and the effects of any valve/pump interlocks.

b) Provide a time history of the water inventory in the R>1ST while the switchover is being performed under the most adverse conditions .relative to time available to perform the necessary .switchover.

c) Xf all pumps are'hut down during switchover, provide

'he time available befo're the core is uncovered.

Res onse to uestion 1 Following an accident the shortest time when the op'erator must take action to perform the necessary switchover is when both trains of ECCS and spray pumps are in .operation at full runout conditions. This is because the RMST is emptying at the fastest possible rate, thus requiring the most rapid operator action to perform the switchover from injection to recirculation.

The limiting times required to switchover the first train of pumps are shown on Figure 1 and the associated RLJST level above the low-low level alarm setpoint (613') is shown-on Figure 2. Once a single train is switched over and operating, an adequate water supply is assured to both the reactor core and the containment sprays. The switchover of the second train supplies redundant capability. The switchover procedure requires stopping only the RHR pumps, the other pumps run continuously while the RHR pumps are shutdo~rn. At no time in. the switchover procedure are all pumps shutdowns Therefore, core uncovery is not expected to occur.

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I<HC uestion 2 The emergency operating procedures permit diversion

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of flow from the low head pumps to the containment spray system.

a) Specify the minimum time after an accident that an operator would be permitted to divert flow from the ECCS system to the containment spray system. Describe the means by which there will be assurance that diversion will not occur prior to this minimum time.

b) Demonstrate that the amount of coolant entering the core, after diversion to containment spray, provides abundant cooling even'ith minimum safeguards equipment available.

c) Confirm that the containment pressure analyses previously presented are consistent trith the responsep to the above questions.

Response to uestion 2 Xn accordance arit the conservative assumptions in Appendix N, Question 0.3.1, Case A, the time where HHR spray diversion is required is approximately 5000 seconds following the accident when containment pressure exceeds 8 psig.

The operating procedure permits diversion of flow from the low head RHR pumps to the residual spray header any time after switchover to recirculation when the containment pressure exceeds 8 psig.

uestion 2b For minimum safeguards, one high head safety injection pump and one charging pump would supply the coolant to the core after realignment of a portion of the RHR pump discharge to the containment sprays. The amount of water which would be supplied to the core at an RCS pressure of 10 psig (which is approximately the peak containment pressure) is approximately 110 ibm/sec. The decay heat mass boiloff at 2755 seconds", which is the minimum time that the KiR pumps can be'diverted to RHH spray, is 62.8 ibm/sec based on the folio~rin assumptions:

• 2755 seconds is the time switchover from injection to recirculation is required with minimum safeguards.

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1. 102$ of Engineered Safeguard Design Rating of $ 391 $ D/t,

2. ANS Infinite Decay Heat with, 20fo Margin (10 CFR 50.46 Appendix K),

3. Coolant entering the core is subcooled by 60 BTU/ibm, Therefore, the coolant entering the Reactor Coolant System piping is about 200/a of that required by the decay heat mass boiloff, calculated with conservative assumptions.

Question 2c The assumptions given in response to guestion 2b above are the emergency core cooling parameters per Appendix K of 10CFR50.

The containment pressure analysis as shown in Appendix N guestion 0.3.1, Case A is. based upon the assumption that the RHR flow is diverted to the sprays at 2755 seconds after the accident. Initiation of RHR spray flow at a time when containment pressure exceeds 8 psig should provide adequate margin to suppress the con-tainment pressure at or below the peak pressure presented in Appendix N, guestion 0.3.1 Case A..

Therefore, the assumptions presented in the response to 2b above" are conservative with respect to the emergency operating procedures related. to diversion of RHR spray flow.

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Attachment 3 Revisions The Abnormal Operating Procedure for switchover

'rom injection to recirculation currently states that the first'step is to check that a sufficient level exists in the sump to assure adequ'ate NPSH exists for the emergency core cooling and containment spray pumps. The procedure states that switchover must begin at the R>JST Low Level Alarm Point. Xf switchover was performed at the time of adequate NPSH in the containment sump, more than adequate time would have been available to perform the switchover since these conditions occur prior to reaching Low Level Alarm Point. However, to assure, under all circumstances, that the operator has sufficient time to perform the switchover, the Low Level Alarm Point on the Refueling

'>later Storage Tank has been raised. This point was revised from 614 ft. (50,754 gallons of useable volume) to 620 ft. (131,961 gallons of useable volume). Conservative calculations show that sufficient NPSH exists when this R>lST Low Level Alarm Point is reached. Our reviews also reveal the necessity to clarify 'the conditions at which the operator would be allowed to perform the switchover and the steps to be taken. 'he procedures are presently being revised to reflect the RNST level change,. steps and parameters for diversion of Attachment A.

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Sruti(oN O.C. COOK t<uCLEnn SVillTCHOVER Tlf'AE FOR VItEST PUMP lNJECTlON TO RECIRCULAT!ON FlGORE i BLOCK AUTO SAFETY STOP N RHR PP STOP W CS CLOSE RHR SUCTION VALVE, CLOSE sz pp MINIFLOiV VALVES OPEN iV RECIRC.

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'P OPEN PATH PP SZ OPEN PATH TO CC PPS IM0-361, ZMO-320 IMO-262/- 263 IMO-306 CS PP rMO-350 -362 N JECTION SIGNAL, PP CHECK (12 SEC-EST) (116.9 SEC) (7.75 SEC) (40.1 SEC) (12 SEC-EST) (9.3 SEC) (4.15 SEC)

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30 SEC 42 SEC 158. 9 166.65 206.75 218. 75 228.05 232. 2 SEC SEC SEC S EC SEC SEC CLOSE iV CS SUCTION VALVE, IMO-225 (60 SEC) 0

1e D.C. COOK NUClEAR STATION REFUELING WATER STOP.AGI:- TAi'~ I(-8>" ITCHOVER HEIGHT ABOVE LOVI-LOVE ALARM FF<OM INJECTION TO RECIRCULATION PHASE TA NYi USEABLE VOLUhIE FEET GALLONS ELEVATION, USEABLE VOLUME VS. TIME I 45,495.68 FIGURE 2 l3I,96l. 22 l7,800 GPM I I 8, 426.76

~ IO) IOO GPM I 04) 892. 30 I

2'?00 8800 GPM 9l, 357. 84 3 77) 823. 38 GPM 64, 288.92 50, 754. 46 LOIV-LOVE ALARM 0 37, 220 IO MINUTES

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