ML20059D151

Intervenor Exhibit I-MFP-151,consisting of LER 2-90-004-00, Re Docket 50-323,dtd 900517

ML20059D151
Person / Time
Site:	Diablo Canyon
Issue date:	08/21/1993
From:	Shiffer J PACIFIC GAS & ELECTRIC CO.
To:
References
OLA-2-I-MFP-151, NUDOCS 9401070034
Download: ML20059D151 (6)

Text

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Nay 17, 1990 '93 GCI 28 P5 51 PG&E Letter No. DCL-90-129 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Nashington, D.C. 20555 Re: Docket No. 50-323, OL-DPR-82 Diablo Canyon Unit 2 Licensee Event Report 2-90-004-00 Containment Ventilation Isolation and fuel Handling Building Ventilation System Shift to Iodine Removal Mode Due to Personnel Error During Troubleshooting Gentlemen:

Pursuant to 10 CFR 50.73(a)(2)(iv), PG&E is submitting the enclosed Licensee Event Report (LER) regarding a containment ventilation isolation actuation and a fuel handling building ventilation system shift from normal mode of operation to iodine removal mode, due to a technician short-circuiting an instrument AC panel during noise troubleshooting. These events constitute Engineered Safety Feature actuations.

This event has in no way affected the public's health and safety.

Kindly acknowledge receipt of this material on the enclosed copy of this letter and return it in the enclosed addressed envelope.

Sincerely, 0$ )

J. D. Shiffer NUCLEAR RECULATORY COMMitt10M

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II. Descriotion of G Lqi l A. Event:

On April 17, 1990, at 2121 PDT, a Unit 2 containment ventilation isolation system (CVIS)(JM) actuation occurred, and the Unit 2 Fuel Handling Building (FHB) ventilation system (VG) transferred to the iodine removal mode, when a voltage transient occurred. The. voltage transient affected the output relays of the containment ventilation-monitor; RM-11 and RM-12, causing the CVI. The voltage transient also momentarily affected the FHB ventilation logic panel POV1, which caused the FHB ventilation system to shift from the normal mode to the  :

iodine removal mode.

1

! The Shift Supervisor contacted the Instrumentation and Controls (I&C) l Department, and the indications received in the control room were

! reviewed. Following an assessment of the alarms and discussion with  ;

j I&C department personnel, the cause of the event was determined to be j l

a voltage tran:ient due to a n>.nentary short in panel PY-21A caused by ]

an I&C technician during troubleshooting of the Gammametrics Post Accident Neutron Flux Monitoring System, Radiation Monitor (IG)(HON)

RM-51. Following this determination, the operators reset the CVI logic and returned the FHB ventilation system to the normal operating ende at 2124 PDT.

i The 4-hour, non-emergency report required by 10 CFR 50.72 was made on April 17, 1990, at 2247 PDT.

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

None.

C. Dates and Approximate Times for Major Occurrences:

l 1. April 17, 1990, at 2121 PDT: Event / Discovery Date: CVI actuated and FHB ventilation system I

transferred to iodine removat mode.

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2. April 17, 1990, at 2124 PDT: The CVI and FHB ventilation system were returned to normal operating modes.

3. April 17,1990, at 2247 PDT: A 4-hour, non-emergency report l required by 10 CFR 50.72(b)(2)(ii) ,

was made.

D. Other Systems or Secondary Functions Affected:

None.

E. Method of Discovery:

Unit 2 control operators were imediately aware of. this event due.to alarms received in the control room.

F. Operator Actions:

After the operators determined that the CVI and the FHB ventilation i system mode shift were due to a voltage transient and that no abnormal radiation levels existed, the operators reset the CVI logic and returned the FHB ventilation system to its normal mode.

G. Safety System Responses:

1. A CVI occurred.

2. The FHB ventilation system transferred from the normal operating mode to the iodine removal e:$ of operation. .

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III. Cause of the Event i l

A. Imediate Cause:

The immediate cause of this event was an electrical short circuit on vital-instrument AC bus PY-21A caused by an I&C technician during electrical noise troubleshooting. This short induced a voltage transient, which caused the radiation monitor _ output relays to momentarily shift to their de-energized (alarm) state, and also caused a momentary loss of power to the logic in:the FHB ventilation system that subsequently resulted in the associated automatic FHB-ventilation system mode transfer.

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J B. Root Cause:

The root cause was determined to be personnel error. An ILC.

technician allowed a test probe to slip during troubleshooting and caused a short between the hot and neutral legs of the Gammanetrics Panel, resulting in a voltage transient. The test probe was designed with a major portion of its conductive surface sheathed, and the I&C technician was aware of the precautions necessary when working on energized circuits. However, the vendor-provided terminal strips located in the panel for incoming AC power are of a design such that the terminals can be shorted if adequate precautions are not followed.

IV. Analysis of the Event Safety Analysis: j The actuation of CVI and transfer of FHB ventilation system-to-the iodine removal mode-are analyzed conditions in the FSAR and_ represent conservative l responses to all affected systems. Therefore, no adverse consequences or i safety implications resulted from this event, and the health and safety of the public were not affected by this event.

V. Corrective Actions A. Immediate Corrective Actions:  :

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1. The CVI and FHB ventilation system were returned to the normal '

operating modes.

2. The technician involved.in the event was counseled.on the necessity for exercising caution in the parformance of maintenance or-testing on energized equipment.

B. Corrective Actions to Prevent Recurrence: 1

1. This event and the maintenance bulletin issued regarding-precautions necessary when working on energized circuits will be reviewed in tailboard meetings with all I6C personnel.

2. This event will be reviewed by all IEC personnel during the next scheduled I&C Ouarterly Training Seminar.

3. Nuclear Engineering and Construction Services (NECS), On-site ~

Plant Engineering Group (OPEG) will evaluate the design and configuration of terminal strips in vendors' cabinets regarding the potential for' shorting when performing maintenance.

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VI. Additional Information A. Failed Components:  :

None.

B. Previous LERs on Similar Events: ,

1. LER 1-87-021 The events are similar in that a CVI was caused when a technician grounded a filter on the line side of a removed fuse during the performance of a surveillance test procedure. The root cause was determi ?d to be personnel error in that the technician failed to realize that part of the circuit was energized. .The corrective action for this event was to include lessons learned from this '

event in a tailboard meeting and in I&C department training. The corrective action for this event would not have prevented the ESF

! actuation because the I&C technician was aware that the circuit-l was energized, and consequently,-had taken appropriate l precautions. l i

2. LER 1-89-001-00 The events are similar in that lifted leads.caus&d a momentary [

loss of AC power. In this event, the loss of power was due to '

l the AC power leads being inadvertently grounded. The corrective action for this event included counseling the technician' regarding precautions when working on energized equipment, .

establishing a policy in the I&C department that energized leads

' not be lifted unless de-energization of equi.nment is undesirable, and briefing I&C technicians on the importance of l

clearing equipment prior to beginning work. T8 a corrective action for this event would not have prevented ESF actuation because the circuit could not be de-energized.

3. LER 1-89-011-00 The events are similar in that a momentary loss of power to a radiation monitor caused a safety system actuation. The momentary loss of power was due to the inadvertent contact ,

between an energized lead and a neutral lead. . The corrective  !

action for this event included counseling the-technician regarding tha precautions necessary when working on energized equipment, and issuing a Maintenance Bulletin-to reemphasize the  !

i need for caution when working on energized equipment. The.  !

corrective actions-for this LER have been effective in reducing. i 31945/0083K 1

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the occurrence rate of ESF actuations caused by AC power transients. They have not completely eliminated these events because it is not always possible to de-energize equipment during maintenance. Additionally, the configuration of circuitry in l the present event was of a design such that the terminals could  :

be easily shorted.

As discussed in PG&E letter DCL-89-254 dsted October'2, 1989, power transients affecting CVI-related radiation monitors have caused several CVIs. Reducing CVIs caused by power transients is being ,

addressed by several corrective actions: training to reduce power.

transients caused by human error; adding CVI bypass switches to allow ,

i disabling of the CVI function during radiation monitor maintenance; and as a further enhancement, PG&E has initiated a Radiation Monitor .

System upgrade program to replace existing radiation monitors with equipment that is less sensitive to power transients. i l

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