05000312/LER-1981-056, Forwards LER 81-056/01T-0.Detailed Event Analysis Submitted

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Forwards LER 81-056/01T-0.Detailed Event Analysis Submitted
ML20039E999
Person / Time
Site: Rancho Seco
Issue date: 12/21/1981
From: Mattimoe J
SACRAMENTO MUNICIPAL UTILITY DISTRICT
To: Engelken R
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20039F000 List:
References
NUDOCS 8201110704
Download: ML20039E999 (2)
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LER-1981-056, Forwards LER 81-056/01T-0.Detailed Event Analysis Submitted
Event date:
Report date:
3121981056R00 - NRC Website
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text

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\\ f NM In accordance with Rancho Seco Nuclear Generatino Station Technical Speci f icat ions Sect ion 6.9.4. I(f) and Regulatory Gui de 1.16 Section C.2.a(6), the Sacramento Municipal Utility District hereoy submits a 14-day follow-up report for Reportable Occurrence 81-5b, which was discussed on December 15, 1981 with the NRC P.esident inspector and confirmed by a telecopied let te r on December 16, 1981.

As discussed in our December 16, 1981 letter, while performing Instrument Surveillance for Peactor Protection System Channel B,

1-108B, with C h a nt:e l C declared administratively inoperable and in Manual Bypass, the Instrument Technician did not follow the procedures properly to insure that the trip system was properly set up to retain the minimum degree of redundancy as required by Technical Specification Sections 3.5.1.1 and 3.5.1.2.

The Plant Review Commit!ce met on December 11, 1981 to consider the use of procedure I-Inf,R uhile Channel C was inoperable One of the final setps of procedure I-108B requires that Channel B is placed in Dypass and the breaker trip-tested to verify operabili'.y.

Since the RPS Sas a oypass interlock feature that prevents more than one channel being in bypass at a tine, a te.mporary chance to the procedure was required.

The Plant Review Committee approved a temporary change that performed the followina general sequence of events:

1.

Channel C is placed in trip condition.

2.

Channel B is placed in bypass and the normal procedure steps are run to the point that the breaker is to be trip tested.

The test holds at that point.

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Channel B is then reset and placed in operate mode.

4.

Channel C is then reset and placed in bypass.

5 The breaker trip test is then performed for Channel B completing 1-108B.

The error on the part of the Instrument Technician occerred at sequence step 1.

Instead of tripping the channel, using the main trip within the Reactor Trip Module, the instrument Technician tripped the Channel C breaker by using the output relay test switches that normally are used in the 1-108 series procedures to simulate a trip. While this does trip the breaker, it does not open the relay contacts in the two-out-of-four relay logic in the other three RPS channels.

This resulted in the other RPS channels' logic remaining in a two-out-of-three condition with only two channels actually operable, since the trip of the Channel C breaker was not fed into the logic of the other channels.

At this point, the RPS was below the minimum degree of redundancy.

Once the test was completed, the Instrument and Controls Engineer reviewed the data and discovered the error. The 16C Engineer reempha-sized to all 16C Technicians that tripping the CPD breakers associated with an RPS channel is not necessarily the same as tripping an RPS channel wi th regard to the ef fects on RPS logic.

The Technical Specifications Table 3.5.1-1 requires that the plant be brought to hot shutdown within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> of the loss of a minimum degree of redundancy.

Since this situation was not determined until after Channel B was back in service with Channel C bypassed, no shutdown was made.

Since the unaf fected channels, A and D, were operable during this event,

providing suf ficient RPS instrumentation to trip the unit if necessary, and since the time the plant was in this condition was short (approxi-mately two hours), there were no adverse effects on plant or public s a f e t y..

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ISE Washington (30)

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