ML20039H234

Forwards Outstanding issue,BSAR-205,re Decay Heat Removal Sys Isolation Capability

ML20039H234
Person / Time
Site:	05000561
Issue date:	07/08/1977
From:	Cox T Office of Nuclear Reactor Regulation
To:	Happell J BABCOCK & WILCOX CO.
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References
FOIA-80-515, FOIA-80-555 NUDOCS 8201190750
Download: ML20039H234 (2)

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2 OUTSTANOING ISSUE, BSAR-205, CONCERNING DHRS ISOLATION CAPABILITY f

STAFF POSITION

' s Power supply assignment to OHR suction line isolation valves inside containment is such that the two valves in series in one of the two redundant trains take power from the same electrical bus.

In the event' R pipe break outside containment, followed by a single failu ae bus, the control room operator would be unable to isolate ene' train.having the failed bus. We find this unacceptable because the' pipe failure would then be unmitigated until a valve a

was closed by an operator outside the control room.

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s-T B & W POSITION x

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w5s Power loss to both valves in one DHR train would require a mechanical failure of an electrical bus, since the bus nas two power sources, (1) ~offsite and (2) diesel generator. B & W says that any single active component failure, up to and including the breakers on the

_ bus feeding the Valve motors, would still leave the bus powered by a.

one of the two available sources. B & W contends that failure of the bus occuring within the sixty seconds required-to close the isolation valve after an assumed DHRS pipe break (also a passive s'

failure) is a scenario too _unlikely to require a modification of

" their current design.

They further contend that the NRC criteria in SRP 3.6.1 support the B & W position.

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