NRC-90-0089, Submits Supplemental Response to NRC Concerns on RHR Operability from Insp Rept 50-341/89-17.Util Faced W/ Decision to Provide Addl Overheating Protection to RHR Sys Pump Vs Maintaining Necessary Water Coverage of Fuel

Submits Supplemental Response to NRC Concerns on RHR Operability from Insp Rept 50-341/89-17.Util Faced W/ Decision to Provide Addl Overheating Protection to RHR Sys Pump Vs Maintaining Necessary Water Coverage of Fuel

ML20043F326
Person / Time
Site:	Fermi
Issue date:	06/04/1990
From:	Orser W DETROIT EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
CON-NRC-90-0089, CON-NRC-90-89 NUDOCS 9006140380
Download: ML20043F326 (3)

Text

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ISOn 'marr"ghway '" oaaaa June 4, 1990 NIC-90-0089 U. S. Nuclear Regulatory Comnission Attn: ; Document Control Desk Washington, D. C. 20555

References:

- 1) Fermi 2 NIC Docket No. 50-341 NIC License No. NPF-43

- 2) NIC Inspection Report No. 50-341/89017, dated January 23, 1990

3) Detroit Edison letter NIC-90-0025, dated February 22, 1990

4) NIC letter to Detroit Edison, dated May 15, 1990

Subject:

' Supplenental Response to NIC Concerns on RHR Ooerability from Insoection Reoort 99017 -

Detroit Edison has reviewed the' NIC evaluation (Reference 4)< of the Eresponse to Inspection Report 89017. Detroit Fdison requests further

' discussion with NIC managenent from. Region III and the Office of f Nuclear Reactor Regulation'on the Residual Heat Removal (RHR)- System

-mininum flow valve -issue. . The purpose of the discussion would' be to achieve u better understanding of. the basis of the NIC position and to present information which may influence the final NIC. position.

1his issue relates' to an event which occurc<d during a plant shutdown.

i when Detroit Fdison took: the RHR mininum-flow valve out of service.

Detroit Edison' took this action during maintenance, in part, to .

prevent the mininum flow line from being available to act as a reactor ;

< vessel ~ drain path to the suppression pool.

This response outlines certain aspects of Detroit Edison's rationale

- on .this issue and also addresses same of the items in Referen s 4.

1) ' Presently, . Detroit Fdison's safety evaluation program does

. address the principles of NSAC-125 as stated in Reference 3.

While NSAC-125 was not published when the safety evaluation in question was written, a safety evaluation program which enphasized the same general principles did exist. Understanding -

. of those general principles was the basis for performing the

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• safety evaluation which allowed the mininum flow valve to be removed from service.

2) As previously stated in Reference 3, the Mm mininum flow line is -

provided to allow a flow path when a Low Pressure Coolant Injection (LPCI) signal occurs, but reactor pressure is too high 4 for LPCI to inject. The mininum flow valve is not needed to perform its related su'p port function while the reactor is shutdown and depressurized because punp cooling is provided by the normal flow of water through the punp as specified in the systen operating procedure. The function of Mm in this case is to be able to inject water into the vessel for decay heat removal. . In the safety evaluation in question, the preparer correctly asserted that the reactor pressure would rerain at the naninal 0 psig and, therefore, the removal of the mininum flow valve did not affect the ability of the Mm system or any of its

-necessary support equipment to perform their function under these circunstances. Based upon the definition of operability, a systen is operable when it is capable of performing its specified function and when all support equipnent necessary for the system to perform its function are capable of performing their related support function (s) . ! Therefore, the Mm system was fully operable with the mininum flow valve disabled closed.

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3) . Detroit Edison could have expressed its position on the H

. probabilities and consequences of a ralfunction of equipnent l inportant to safety associated with removing the mininum flow i valve from service more clearly in Reference 3. Mequate cooling i for the Mm pung was provided by flow through the punp while

+ operating in this mode. This cooling could_ only be lost if the discharge path was blocked which would be~ caused by a failure, q The same failure would also prevent the Mm systen from "I performing its function. A failure is not required to be assumed "

when assessing operability. 'Ihe probability of losing the. flow through the' punp was not-increased by removing the valve from service. The consequences'of a malfunction of equipnent

igartant to safety were decreased by disabling the mininum flow ~

valve. . The consequences of a malfunction that blocks Mm' pump discharge flow is a loss of Mm function whether or not the mininum flow valve is in service. The radiological consequences could be more severe if the minimum flow valve: opened depending -

on how far the reactor vessel drained down and evolutions in progress. Therefore, neither the probability or consequences of a n:alfunction of equignent inportant to safety were increased while the mininum flow valve was disabled closed.

-4) Detroit Edison committed to conplying with Regulatory Guide

-1.139, which requires that design features and operating procedures be in place to prevent damage to the pumps. Detroit Edison conplies with this Regulatory Guide by the following j

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i methcxis. First, an operating procedure exists which covers all modes of operation of the RHR systen. Secondly, design features I were provided which include (1) a mininum flow line to prevent

! damage to the punps due to. overheating when the injection valves are closed because raactor. pressure is too' high to permit injection artl (2) a flow path through the punp when reactor.

L pressure is below the shutoff head of the punps such as when in the shutdown cooling node.

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,. 5) From an overall safety perspective, Detroit Edison is faced with l l choosing to provide additional overheating protection to the RHR l1 system punp versus maintaining (and not challenging) necessary - a water coverage of the fuel. If Detroit Edison' relied solely on j the reactor. vessel low level 3 isolation signal to provide vessel i drainage protection, there is a possibility the mininum flow line ';

could serve as a drain path until water level has dropped _

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, significantly. A vessel draindown, which has occurred several  ;

l tines in. boiling water reactors, will lead. to a reduction in shielding and the possibility of uncovery of any fuel. The level p 3 trip is well below the reactor vessel flange. . Based upon these l facts, Detroit Edison considers it prudent to disable the mininum .

L flow valve in the closed position under these conditions. -l 1

Detroit Edison believes further cmuunication on- the mininum flow _

L _ valve issue is inportant so a nutual understartling can be achieved.  !

l' Please review the rationale described here and then contact Lynne 1 Goodman at (313) 586-4211' to arrarv3e for the requested meeting.

l L Sincerely, i l-1, 5 W. S. Orser _l i Senior Vice President _

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cc .A. B. Davis 1 R.' W.,DeFayette '1 L W. G. Rogers

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