ML18093A307

LER 83-014/03L-1:on 830413 & 18,operating Loads on 2A 4kV & 460-volt Vital Buses Observed to Trip.Caused by Spurious Operation of Safeguards Equipment Control Sys Due to Design Deficiencies.Equipment restarted.W/870812 Ltr

ML18093A307
Person / Time
Site:	Salem
Issue date:	08/12/1987
From:	Frahm R, Zupko J Public Service Enterprise Group
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
LER-83-014-03L, LER-83-14-3L, NUDOCS 8708190167
Download: ML18093A307 (5)

Text

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£IIJ !On two separate occasions on April 13 and April 18, 1983, operating loads on the No.

)))) 2A 4kv and 460V Vital Buses were observed to trip. In both cases, due to the de-1

))1] 1energization of No. 21 Residual Heat Removal (RHR) Pump, No. 21 RHR Loop was no longer I

)))) lin operation, and Action Statement 3.4.l.4b-was entered. In each instance, the RHR

)))) r.oop was immediately returned to operationi no reduction in Reactor Coolant System 1

III) I boron concentration occurred. The events constituted operation in a degraded mode in accordance with Technical Specification 6.9.l.9b.

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CAUSE DESCRIPTION ANO CORRECTIVE ACTIONS @

I!2J I The root cause of the SEC events is attributed to equipment electrical design JJJJ  !"deficiencies. These deficiencies have been corrected by the installation of equipment!

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Public Service Electric and Gas Company P.O. Box E Hancocks Bridge, New Jersey 08038 Salem Generating Station August 12, 1987 U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Dear Sir:

SALEM GENERATING STATION LICENSE NO. DPR-75 DOCKET NO. 50-311 UNIT NO. 2 LICENSEE EVENT REPORT SUPPLEMENT 83-014/03L-l This supplemental Licensee Event. Report is being submitted pursuant to the requirements of 10CFR 50.73 and Technical Specification 6.9.1.7. LP.F 83-014/03L has been revised to specify the root cause of the event and to detail the corrective actions taken.

Sincerely yours, J.~tt.ft General Manager-Salem Operations

.MJP:pc Distribution The Energy People 9~,-2* 89 I~ 1Ml,2-84

~eport Number: 83-o:9o3L-l .e Report Date: 08-12-87 Occurrence Date: 04-13-83 Facility: Salem Generating Station Unit 2 Public Service Electric & Gas Company Hancock's Bridge, N. J~ 08038 IDENTIFICATION OF OCCURRENCE:

Reactor Coolant System - Residual Heat Removal Loops - Loss of Operating Loop This report was initiated by Incident Reports83-071 and 83-072.

CONDITIONS PRIOR TO OCCURRENCE:

Mode 5 - Rx Power 0% - Unit Load 0 MWe.

DESCRIPTION OF OCCURRENCE:

On two separate occasions, ~t 1755 hours0.0203 days <br />0.488 hours <br />0.0029 weeks <br />6.677775e-4 months <br />, April 13 and 1520 hours0.0176 days <br />0.422 hours <br />0.00251 weeks <br />5.7836e-4 months <br />, April 18, 1983, operating loads on the No. 2A 4KV and 460V.Vital Buses were observed to trip. The only indications received in the Control Room were alarms assocated with the loss of the running equipment and flashing bezel stop pushbuttons. Two different vital bus power sources were involved; on both occasions the infeed breaker remained closed. In both cases, due to the deenergization of No~ 21 Residual Heat Removal (RHR) Pump, No. 21 RHR Loop was no longer in operation.

Due to no RHR Loop being in operation, Technical Specification Action Statement 3.4.l.4b was entered. In each instance, the RHR loop was

• immediately returned to operation, and no reduction in Reactor Coolant System (RCS) boron concentration occurred with the RHR loop out of service.

APPARENT CAUSE OF OCCURRENCE:

Investigation revealed that the occurrences were evidently due to spurious operation of the Safeguards Equipment Control (SEC) System.

Previous spurious actuations related to control circuitry noise (see LER 82-132/03L) had been addressed by installation of noise

• suppression devices (per_ Design Change Request 2EC1387). *However, investigation has shown*these problems to be unrelated.

The root cause of the SEC related events addressed in this LER and

• Unit 2 LER's 83-025/93L, 83-031/B3L, 83-941/03L, 83-04.7/03L, and 83-059/03L was equipment design deficiencies. Investigation of these SEC related events revealed:

1. The. SEC is very susceptible to voltage transients due to the design of its electronics;

2. Because the SEC doe.s not have surge suppression components across the DC reactive components, such as the breaker-closing coils, large voltage transient.s *are induced in the SEC by DC currents that interface with it;

- 3. Occassionally, the .AC .power source to the SEC experiences transients in voltage;

• LER 83-014/03L-l APPARENT CAUSE OF OCCURRENCE: (cont'd)

4. The SEC has an auto-test-feature which eventually causes the relays to wear out. The test involves the relays flexing their armature and' rubbing contacts approximately every second, which taxes them; and S. Radio frequencies (RF), such as from hand held radio transmissions used by Security and Fire Protection, can interfere with the SEC's electronics.

ANALYSIS OF OCCURRENCE:

Operability of the RHR loops is required to provide heat removal capability for removing decay heat. A single loop provid~s sufficient capability; single failure considerations require that two loops be operable. A single RHR pump also provides adequate flow to ensure mixing; prevent stratification and-produce gradual reactivity changes during RCS boron concentration reductions.

As noted, in both instances, RHR flow was immediately restored and no reduction.in boron concentration occurred. The events therefore -

• involved no undu~ risk to the health of safety of the public. The occurrences constituted operation in a degraded mode permitted by a limiting condition for operation and are reportable in accordance with Technical Specification 6.9~1.9b.

Action Statement 3.4.l.4b requires:

With no RHR loop in operation, suspend all operations involving a reduction in boron concentration of the RCS and immediately initiate corrective action to return the required RHR loop to operation.

CORRECTIVE ACTION:

ln both cases, after a survey of the control board showed no other

_abnormalities, the Control Room Operator restarted appropriate equipment. In each instance, No. 21 RHR Pump was restarted to restore an RHR loop to operation, and Action Statement 3.4~1.4b *was terminated_

at 1756 hours0.0203 days <br />0.488 hours <br />0.0029 weeks <br />6.68158e-4 months <br />, April 13 and at 1520 hours0.0176 days <br />0.422 hours <br />0.00251 weeks <br />5.7836e-4 months <br />, April 18,. 1983.

New 24V and 15V power supplies were installed (per DCR 2EC-1778).

These power supplies are more reliable and steadier than the previous ones. Additionally, the supply voltage was raised from 15 to 16 volts for all SEC Cabinets. Time delay relays were installed (per Design Change Request 2EC-1778) to offer protection from brief, spurious voltage transients. The cables between the SEC electronics and the input relays were shielded (via Design Change Request 2EC-1898) to minimize spurious activity and RF interference concerns.

Administrative Controls prohibit the use of radio transmitters in the vicinity of the SEC.

• Engineering Field Directive S-SC-Rl30-CFD-251, nMaintenance of Safeguards Equipment Controller (SEC) Relaysn recommendations were implemented. These recommendations include checking the SEC relays every refueling outage utilizing a nrelay testern. Those relays which

LER 83-014/03L-l CORRECTIVE ACTION: (cont'd) demonstrate degraded performance are replaced. Upon completion of relay testing the SEC js tested for operability (Operations Department procedure SP(0)4.3.2.l(a)).

After implementation of the above corrective actions, the 2A SEC Cabinet was monitored for approximately six (6) n1onths. No addi~ional similar spurious actuations were identified.

FAILURE DATA:

Automation Industries, Inc.

Safeguards Equipment Control System GeY:::~

Salem Operations MJP/pc SORC f.1tg.87-061 I