ML20024G743

LER 91-006-00:on 910325,toxic Gas Isolation Sys Train a Actuated on High Ammonia Gas Level While Troubleshooting 910324 Failure of Channel.Caused by Location of Jumper Used to Bypass Circuitry.Jumper Will Be relocated.W/910424 Ltr

ML20024G743
Person / Time
Site:	San Onofre
Issue date:	04/24/1991
From:	Krieger R SOUTHERN CALIFORNIA EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-91-006-01, LER-91-6-1, NUDOCS 9104290234
Download: ML20024G743 (5)

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IITATKJN MANACAF R g 7 se, ; egg eggg April 24, 1991 U. S. Nuclear Regulatory Commission Document Control Desh Wainington, D.C. 20$$$

Subj ect: Docket No. 50 361 30 Day Report Licensee Event Report No. 91 006 San Onofre Nuclear Generating Station, Unit 2 Pursuant to 10 CFR 50.73(d), this submittal provides the required 30 day written Licensee Event Report (LER) for an occurrence involving the Toxic Cas Isolation System (TGIS). Since this occurrence involves areas common to both in Units 2 and 3, a single report for Unit 2 is being submitted in accordance with INREG-1022. Neither the health nor the safety of plant personnel or the -

public was affected by this occurrence.

If you require any additional information, please so advise.

Incerely, T

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Enclosure:

LER No.91-006 cc: C. W. Caldwell (USNRC Senior Resident Inspector, Units 1, 2 and 3)

J. B. Martin (Regional Administrator, USNRC Region V)

Institute of Nuclear Power Operations (INPO) 9104290234 910.';24 fffQ PDR ADOCK 0".000361 i S PDR /// I

LICENEEE ETENT REfVRT (LER)

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t!CEN"EE CONTACT FOR T!!!B LER (12)

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$UFF1.EMENTAL REIVRT EXPECTED (14) Nnth Day for Expected Suter.is s ion

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At 1530 on March 25, 1991, wit.h Unit 2 at 60% power and Unit 3 at 100% power, Toxic Gas Isolation System (TGIS) Train "A" actuated on high ammonia gas level, All TGIS Train "A" components were verified to have actuated as required.

The actuation occurred while troubleshooting was being performed on the Train "A" ammonia channel, which had failed on March 24, 1991. A Maintenance technician inadvertently bumped the jumper used to bypass the TGIS actuation circuitry, resulting in the jumper being inomentarily dislodged. Since the ammonia level had been increased above the actuation setpoint to perform the troubleshooting, an actuation on high ammonia occurred.

The root cause of this event is that the location of the jumper used for bypassing the TGIS actuation circuitry was adjacent to the area requiring access during maintenance activities. Therefore, a potential existed for disturbance of the jumper during these activities, for corrective actions: 1) appropriate disciplinary action has been administered to the technician involved in this event, 2) this event has been reviewed with appropriate Maintenance personnel, and 3) the bypass jumper, when installed in the future, will be relocated to an area less likely to be affected by maintenance activities.

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION SAN ONOFRE NUCLEAR GENERATION STATION DOCKET NUMBER LER NUMBER PAGE UNIT 2 0500036] 91-006 00 2 of 4 Plant: San Onofre Nuclear Generating Station Units: Two e,nd Three Reactor Vendor: Combustion Engineering Event Date: 03 25 91 A. CONDITIONS AT TIME OF Tile EVENT:

Mode: 1, Power Operation (Units 2 and 3)

B. BACKGROUND INFOR!iAT10N:

The common Unit 2 and 3 control room is designed to be automatically isolated by the Control Room Emergency Air Cleanup System (CREACUS) [VI) to prote::t personnel f rom potential outside airborne radiation or toxic gas contaminat. ion. CREACUS is started in the isointion mode when the Toxic Cas Isolation System (TGIS) [VI] detects chlorine, ammonia or butane (hydrocarbon) gas in the outside air intake. Technical Specification Limiting Condition for Operation (LCO) 3.3.2, " Engineered Safety Features Actuation System," er.tablishes TGIS operability requirements.

There are two independent trains of both CRrJsCUS and TGIS. Each train io actuated by either a remote manual puah button switch (PB) [IIS), a gas concentration sensed by any of the gas detectors (DET) which is above the actuation setpoint, or a loss of power. Each CREACUS train closes all control room air intake and exhaust pathways [DMP), and recirculates the air inside the control room spaces through HEPA filters [FLT] and charcoal adsorbers [AD5;.

C. DESCRIPTION OF Tile EVENT:

1. Event:

At 1530 on March 25, 1991, with Unit 2 at 60% power and Unit 3 at 100% power, TCIS Train "A" actuated on high ammonia gas level. All TCIS Train "A" components were verified to have actuated as required.

At the time of the actuation, troableshooting was being performed on the Train "A" ammonia channel, which had failed low on March 24, 1991. Specifically, a Maintenance technician (utility, non-licenood) was disconnecting the Digital Multimeter (DRM) used during troubleshooting from its connection locations internal to the TGIS cabinet. During this process, the technician inadvertently bumped one of the connections of the jumper used to bypass the TGIS actuation circuitry. This resulted in the jumper becoming momentarily dislodged. The technician quickly re connected the jumper; however, since the ammonia level had been increased above

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1.1CENSEE EVENT REPORT (LER) TF.XT C0!iTINUATION SAN ONOFRE NUCLEAR GENERATION STATION DOCKET NUMBER LER NUMBER PAGE UglT 2 05000361 91 006-00 3 of 4 the actuation setpoint to perform the troubleshooting, an actuation on high ammonia occurred.

2. Inoperable Structures, Systems or Components that Contributed to the Event:

Not spplicable.

3. Sequence of Events:

DATE TIME ACTION 3/24/91 0800 TGIS Train "A* ammonta channel fails low.

3/25/91 1530 TOIS Train "A" actuation on high ammonia leswl during troubleshooting.

3/25/91 1600 Control room ventilation lineup returned to normal.

3/26/91 0330 TGIS Train "A" returned to service.

4. Method of Discovery:

Control room alarms and inGications alerted the operators of the TGIS actuation.

5. Personnel Actions and Analysis of Actions:

The operators responded properly to the TOIS netuation by 1) verifying proper system operation and 2) determining that the ammonia level was normal prior to returning TGIS to the " standby" mode and restoring normal control room ventilation.

6. Safety System Responses:

The TOIS and CREACUS systems functioned in accordance with their design.

D. CAUSE OF Tile EVENT:

1. Immediate cause:

During troubleshooting of the TGIS Train "A" ammonia channel, the Maintenance technician inadvertently bumped one of the connections of the jumper used to bypass the actuation circuitry. This resulted

in the jumper being momentarily dislodged. Since the ammonia level had been increased above the actuation setpoint to perform the troubleshooting, an actuation on high ammonia occurred, i

LICENSEE EVENT rep 0RT (LER) TEXT CONTINUATION SAN ONOFRE NUCLEAR GENERATION STATION DOCKET NUMBER LER NUMBER pAGE UNIT 2 ;QhB00361__ 91 006 00 4 of 4

2. Root Cause:

'The location of the jumper used for bypassing the TGIS actuation circuitry was adjacent to the area requiring access during maintenance activities. Therefore, a potential existed for disturbance of the jumper during these activities.

E. CORRECTIVE ACTIONS: r l l

1. Corrective Actions taken:,

a. Appropriate disciplinary action has been administered to the technician involved in this event. >

b. This event has been reviewed with appropriate Maintenance personnel. t

2. Planned Corrective Action:

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The bypas's jumper, when installed in the future, will be relocated '

to an area less-likely to be affected by maintenance activities.

Specifically, the inputs on the terminal strip to which the oypass jumper is connected will be relocated to the opposite side of the strip. When this is completed, al1~the terminal strip inputs used for connecting test equipm6nt will be on one side of the terminal strip and the bypass jumper will be on the other, Therefore, installation and removal of the test equipment (such as a DKM) should not interfere with the bypass jumper.

F. . SAFETY SIGNIFICANCE OF THE EVENT:

There is no safety significance to this event since all TGIS and CREACUS components operated as designed.

0. ADDITIONAL INFORMATION;-

L 1. Component Failure Information:

f

Not applicable.

2, Previous LERs for Similar Events:

LER $6 034 (Docket No. 50 361) reported two TGIS actuations caused by the bypass jumper being dislodged during the performance of maintenance activities. As a result of these actuations, the design-

- of the bypass jumper was changed and the location of the jumper was moved to minimize recurrence. The event being reported in this LER _ '

is the first TGIS actuation caused by the bypass jumper since these corrective actions.

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