ML18095A838

LER 91-006-00:on 910302,ESF Actuation,Automatic Switching of Control Room Ventilation to Emergency Mode of Operation Occurred.Caused by Equipment Failure.Channel Detector Cable Connection rebuilt.W/910401 Ltr

ML18095A838
Person / Time
Site:	Salem
Issue date:	04/01/1991
From:	Labruna S, Pollack M Public Service Enterprise Group
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-006-01, LER-91-6-1, NUDOCS 9104050272
Download: ML18095A838 (5)

Text

Public Service Electric and Gas Company P.O. Box 236 Hancocks Bridge, New Jersey 08038 Salem Generating Station April 1, 1991 u. s. Nuclear Regulatory Commission Document Control Desk DC 20555

Dear Sir:

SALEM GENERATING STATION LICENSE NO. DPR-75 DOCKET NO. 50-311 UNIT NO. 2 LICENSEE EVENT REPORT 91-006-00 This Licensee Event Report is being submitted pursuant to the requirements of the Code of Federal Regulations lOCFR 50.73(a) (2) (iv). This report is required within thirty (30) days of discovery.

MJP:kll Distribution

* .. ; -. . "* f * :* * ..-(.:; ,* . 9104050272 910401 PDR ADOCK PDF Sincerely yours, s. LaBruna General Manager -Salem Operations 95-2189 (10M) 12-89 '

NRC Form 31141 19-831 U.S .. NUCLEAR REGULATORY COMMllllON A,.ROVED OMI HO. 31!!0-4104 LICENSEE EVENT REPORT (LER) EXPIRES: 8/311115 FACILITY NAME 111 !DOCKET NUMBER 121 I l;!I Salem Generatinq Station -Unit 2 o 15 Io IO Io 13 fl 11 1 loF o 14 TITLE (4) *EsF Actuation Siqnals: 2RlA Channel Failure Causinq Cm trol Room Vent. Switch EVENT DATE (SI LEA NUMBER 1111 REPORT DATE 171 OTHER FACILITIES INVOLVED 191 MONTH DAY YEAR YEAR tt tt MONTH DAY YEAR FACILITY NAMES DOCKET NUMBERISI O 1s1010101 I I Ol'EAATIHO MOOE Ill THll REPORT 11 IUIMITTED PURSUANT TO THE REQUIREMENTI OF 10 CFR §: (Clr<<:k ono or more ol th* lo/lowing/

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--ll0.73'-112111111 LICENSEE CONTACT FOR THll LER 1121 NAME TELEPHONE NUMBER AREA CODE M. J. Pollack -LER Coordinator COMP'LETE ONE LINE FOR EACH COMPONENT FAILURE DESCRllED IN THIS REPORT 1131 CAUSE SYSTEM COMPONENT I I I I I I I I MANUFAC* TUR ER I I I I I I SUPPLEMENTAL REPORT EXPECTED 1141 lxl YES (II Y"* comp/ere EXPECTED SUBMISSION DATE! AISTRACT (Limlr ro 14()() l/>>CH, I.* .* *pproxim*rely

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fYi>>-tren linHI (181 I I I I I I I I MANUFAC* TUR ER I I I I I I EXPECTED DATE 1151 MONTH DAY YIOAR On 3/2/91 at 2054 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.81547e-4 months <br />, during normal plant operation, the Control Room general area Radiation Monitoring System (RMS) monitor (2RlA) spiked high. This resulted in the automatic switching of the Control Room ventilation from normal operation to its.accident mode of operation (100% recirculation).

The switching of* the Control Room ventilation system to its emergency mode of operation is an Engineered Safety Feature (ESF). The cause of this event was determined to be a failed detector cable connection.

The channel was subsequently returned to service on 3/4/91. On 3/5/91 at 1754 hours0.0203 days <br />0.487 hours <br />0.0029 weeks <br />6.67397e-4 months <br />, a second automatic ventilation switching occurred from a 2R1A RMS channel low failure signal. During this event, one of the ventilation outlet dampers (2CAA18) did not close fully. Investigation of this second event did not identify the specific cause; however, the channel backplane was rebuilt and the first op-amp was replaced.

The root cause of both events is attributed to equipment failure and equipment design concerns.

Periodic problems with the Unit 2 RMS system have been experienced as indicated in prior LERs (e.g., 311/90-044-00).

The channel failed components were repaired/replaced as applicable.

The 2CAA18 linkage arm was repaired.

Several system design modifications should eliminate the spurious ESF actuation signals. These design modifications include a proposal for RMS channel equivalent replacement.

NRC Form 3911 19.aJI I LICENSEE EVENT R.EPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 2 DOCKET NUMBER 5000311 PLANT AND SYSTEM IDENTIFICATION:

Westinghouse Pressurized Water Reactor LER NUMBER 91-006-00 PAGE 2 of 4 Energy Industry Identification System (EIIS) codes are identified in the text as f xxt IDENTIFICATION OF OCCURRENCE:

Engineered Safety Feature Actuation Automatic Switching of the Control Room Ventilation to the Emergency Mode of Operation Due to Equ:j..pment Failure and Equipment Design Concerns.

Event Dates: 3/02/91 and 3/05/91 Report Date: 4/01/91 This report was initiated by Incident Report Nos. 91-:157 and 91-163. CONDITIONS PRIOR TO OCCURRENCE:

Mode 1 Reactor Power 100% -Unit Load 1160 MWe DESCRIPTION OF OCCURRENCE: . . On March 2, 1991 at 2054 hours0.0238 days <br />0.571 hours <br />0.0034 weeks <br />7.81547e-4 months <br />, during normal plant operation, the Control Room general area Radiation Monitoring System (RMS) f ILi monitor (2R1A) spiked high. This resulted in the automatic switching of the Control Room ventilation from normal operation to its accident mode of operation (100% recirculation).

As addressed in the Apparent Cause of Occurrence section, the cause of the automatic ventilation switching was identified and The was subsequently returned to service on March 4, 1991. On March 5, 1991 at 1754 hours0.0203 days <br />0.487 hours <br />0.0029 weeks <br />6.67397e-4 months <br />, a second automatic ventilation switching occurred from a 2R1A RMS channel low failure signal. During this event, one of the ventilation outlet dampers (2CAA18) did not close fully. The switching of the Control Room ventilation system to its emergency mode. of operati6n is an Engineered Safety Feature (ESF). Therefore, on March 2, 1991 and March 5, 1991 at 2205 and 1830 hours0.0212 days <br />0.508 hours <br />0.00303 weeks <br />6.96315e-4 months <br /> respectively, the Nuclear Regulatory Commission was notified of the automatic switching in accordance with Co_de of Federal Regulations

• .lOCFR 50.72(b)(2)(ii).

i I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 2 APPARENT CAUSE OF OCCURRENCE: . DOCKET NUMBER 5000311 LER NUMBER 91-006-00 PAGE 3 of 4 The root cause of these events is attributed to both equipment failure (detector connection) and equipment design concerns (no specifically identified faults). The type .detector system used for the Salem Unit 2 RMS channels is manufactured by Victoreen.

Periodic problems with this system have been experienced as indicated in prior LERs (e.g., 311/90-044-00}.

Investigation of the March 2, 1991 event identified that movement of the detector cable would cause spurious high channel spikes. Subsequently, the detector cable connector was rebuilt. The channel was then calibrated and functionally checked-successfully.

• It was. returned to service* on March 4, 1991. Investigation of the March 5, 1991 event did not identify the specific cause of the channel failure. ;However, the channel backplane was rebuilt and the first stage operational amplifier was replaced (based on prior experience).

• ANALYSIS OF OCCURRENCE:

The 2R1A detector is a Victoreen 857-20, GM tube. It is the Unit 2 Control Room general area radiation monitor and monitors ambient gamma. radiation levels. Generally, the 'control Room dose rate would increase due to the intake of radioactive materials.

Therefore, the Control Room intake duct is isolated and the ventilation air is put in full recirculation through HEPA and Charcoal filters. This design is in accordance with the Updated Final Safety Analysis (UFSAR) which requires protection of Control Room personnel during a loss-of-coolant accident (LOCA), by limiting whole body dose to 5 rem, or its equivalent to any part of the body. The 2R1B Control Room intake duct radiation monitor is used to corroborate the 2R1A channel readings.

It too has the same automatic isolation function.

During this event, no increase of activity was noted. As stated in the of Occurrence section, the 2CAA18 outlet damper did not close fully after initiation of the ventilation switching signal. Investigation revealed that the linkage arm allen screws had loosened.

The 2CAA19 outlet valve is in series with the 2CAA18 damper.* It operated satisfactorily.

Therefore, the failure of the 2CAA18 damper did not affect the Control Room ventilation switching.

I

• I LICENSEE EVENT REPORT (LER) TEXT CONTINUATION Salem Generating Station Unit 2 DOCKET NUMBER 5000311 ANALYSIS OF OCCURRENCE: (cont'd) LER NUMBER 91-006-00 PAGE 4 of 4 As *.indicated previously, the automatic switching of Control Room ventilation to its accident mode of operation was not caused by high radiation levels, but by concerns.*

Also, the failure of the 2CAA18 valve did not prevent Control Room ventilation switching (due to operability of the 2CAA19 damper). Therefore, the health and safety of the public was not affecteq by this event. However, since the Control Room ventilation switching to the accident mode of operation is an ESF, this event is reportable in accordance with Code of Federal Regulations lOCFR 50.73(a) (2) (iv). CORRECTIVE ACTION: The channel detector cable connection was rebui1t. The 2R1A channel backplane was and the first stage operational amplifier was replaced.

The 2CAA18 linkage arm was repaired.

Equipment with similiar types of linkage configuration will be inspected.

The results of the inspections will be assessed to determine whether the existing preventive maintenance program on these dampers provides adequate assurance of damper.integrity.

After completion of the 2R1A channel repairs and 2CAA18 linkage arm repairs, a subsequent 2R1A alarm, for communications failure, was received.

This alarm indicates a problem between the channel and its Central Processing Units (communications failure).

Additional investigation is in progress.

As indicated in prior LERs (e.g., LER 311/90-044-00), Engineering has investigated the concerns with the Unit 2 RMS channels.

It is anticipated that several system design modifications wi.11 eliminate the spurious ESF actuation signals. These design modifications include a proposal for RMS channel equivalent replacement.

MJP:pc SORC Mtg.91-040

___ _ General Manager -Salem Operations