DCL-89-117, Special Rept:On 890406,main Steam Line Radiation Monitor 1RM-71 Alarmed & Declared Inoperable.Caused by Failure of Detector Tube.Tube Replaced.Monitor Returned to Svc on 890418

Special Rept:On 890406,main Steam Line Radiation Monitor 1RM-71 Alarmed & Declared Inoperable.Caused by Failure of Detector Tube.Tube Replaced.Monitor Returned to Svc on 890418

ML20245J147
Person / Time
Site:	Diablo Canyon
Issue date:	04/27/1989
From:	Shiffer J PACIFIC GAS & ELECTRIC CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
89-04, 89-4, DCL-89-117, NUDOCS 8905040017
Download: ML20245J147 (5)

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• ' Pscific Gas and Electric Company 77 Beale Street James D. Shiffer San Francisco,CA 94106 Vice President 4151972 7000 Nuclear Power Generation TWX 910-372 6587 April 27, 1989 PG&E Letter No. DCL-89-117 U.S. Nuclear Regulatory Commission

-ATTN: Document Control Desk Hashington, D.C. .20555 Re: Docket No. 50-275, OL-DPR-80 Diablo Canyon Unit 1 Special Report 89-04, Inoperability of Unit 1 Main Steam Line Radiation Monitor RM-71 Gentlemen:

In accordance with the requirements of Diablo Canyon Technical Specifications 6.9.2 and 3.3.3.6 Action d., the enclosed Special Report is submitted to report the Unit 1 main steam line radiation monitor RM-71 being-inoperable for greater than seven dayr.

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, m

. N J. D. S fer cc: J. B. Martin M. M. Mendonca P. P. Narbut H. Rood B. H. Vogler CPUC Diablo Distribution Enclosure NCR DC1-89-TI-N043 2672S/0068K/JHA/2245 S.

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PG&E Letter No. DCL-89-117 ENCLOSURE INOPERABILITY OF UNIT 1 MAIN STCA'M LINE RADIATION MONITOR RM-71 u 'I. P.lant Conditions Unit I was in Mode 1 (Power Operation) at approximately 100 percent power.

II. Description of Event A. Event:

On April 6, 1989 at 1743 PDT, Unit 1 main steam line radiation monitor 1RM-71 olarmed and was declared inoperable. Technical Specification (TS) 3.3.3.6 Action d. was entered and noted on the '

operators' TS status sheet requiring a return to service within 7 days or a special report submitted to the NRC within 14 days thereafter in accordance with TS 6.9.2. The Shift Supervisor notified the responsible department manager of the 7-day TS action.

On April 7, IRM-71 was removed from service in accordance with Surveillance Test Procedure (STP) I-18R28, " Source Calibration of the Detectors for the Main Steam Line Monitors," and work order C0051970 was initiated for troubleshooting and repair. Troubleshooting revealed that the detector tube had failed. The detector tube was l

, replaced and calibration per STP I-18R2D was started on April 8.

On April 8'at 1770 PDT, in accordance with Surveillance Test l

Procedure (STP) G-16. " Alternate Methods of Monitoring for High Range Post Accident Radiation Monitors," alternate equipment was placed in effect within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> of 1RM-71 inoperability.

During calibration on April 9, the new detector tube exhibited poor response and then failed. A second new detector tube was installed and calibration started on April 11.

During calibration on April 12, the log rate meter printed circuit r board did not respond properly and was determined to be defective.

It was replaced on April 13 and calibration was again restarted.

On April 13,1989 at 1743 PDT, TS 3.3.3.6 Action d. time limit was exceeded as 1RM-71 was inoperable for more than 7 days.

Between April 14 and April 18, I&C technicians completed calibration testing of 1RM-71 in accordance with STP I-18R28. On April 18, 1989 at 0954 PDT, functional testing was completed, IRM-71 was returned to service, and the TS action statemant was exited.

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

-None.

C. Dates and Approximate Times for Major Occurrences:

April 6.1989,1743 PDT 1RM-71 alarmed and was declared inoperable.

L April-7, 1989 1RM-71 was removed from service and

[ troubleshooting revealed that the detector tube had failed.

April'8,.1989 Detector tube was replaced and calibration was started.

April 8,1989 -1770 PDT Alternate monitoring equipment placed into effect.

April 9, 1989 New detector tube exhibited poor response and then failed. Second new detector tube was installed.

April 11, 1989 Calibration was started with detector tube giving satisfactory indications.

April 12, 1989 Continued calibration revealed that log rate meter printed circuit board was not responding properly.

April 13,1989 Log rate meter printed circuit board was replaced and calibration was restarted.

April 13, 1989, 1743 PDT Event date: T.S. 3.3.3.6 Action d. seven day time limit exceeded.

April 18, 1989, 0954 PDT 1RM-71 returned to service and TS action statement was exited.

D. Other Systems or Secondary Functions Affected:

None.

E. Method of Discovery:

Inoperability of 1RM-71 was immediately apparent in the control room due to alarms and indications.

F. Operator Actions:

Unit 1 RM-71 was declared inoperable and Action Request (AR) A0145424 was initiated to repair the monitor.

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6 G. Safety system responses:

None.

. III. Cause of the Event A. Immediate Cause:

A detector tube failure caused the inoporability of 1RM-71. '

B. Root Cause:-

Equipment failures during calibration of 1RM-71 (detector tube and log rate meter-printed circuit board) coupled with the time required to calibrate this channel resulted in IRM-71 being inoperable in excess of the the seven day time. limit of TS 3.3.3.6 Action d.

IV. Analysis of the Event The main steam line (MSL) radiation monitors are used in DCPP emergency operating procedures and emergency response assessment procedures to aid in the determination of radiation doses resulting from a steam generator tube ruptere (SGTR) event. TS 3.3.3.6 Action d. requires that if a monitor is inoperable, preplanned L1 ternate methods of monitoring the MSL parameters shall be initiated within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. In accordance with Surveillance Test Procedure (STP) G-16. " Alternate Methods of Honitoring for High Range Post Accident Radiation Monitors," alternate equipment was placed in effect within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to monitor main steam line dose rates in event of a SGTR.

Based upon the continuous availability of the alternate monitoring methods, this event would not have resulted in any loss of capability to respond to any postulated accident. Therefore, there were no adverse -

safety consequences or implications resulting from this event.

V. Corrective Actions A. Immediate Corrective Actions:

1. IRM-71 was declared inoperable and the alternate method of monitoring the main steam lines was initiated in accordance with TS 3.3.3.6 Action d. and STP G-16.

2. Following replacement of the failed detector tubes and the log rate meter printed circuit board, 1RM-71 was returned to service on April 18, 1989.

B. Corrective Actions to Prevent Recurrence:

No corrective actions are deemed necessary to prevent recurrence of this event based on the multiple equipment failures coupled with the time required to calibrate this channel.

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VI. Additional Information A. Failed Components:

1. Detector tubes (2): Victoreen no. 910632, warehouse stock code 94-0748.

2. Log rate meter printed Victoreen no. 842-10-30, circuit board: warehouse stock code 93-7017.

B. . Previous Special Reports on Similar Events:

The following Special Reports are related to exceeding the 7-day time ,

limit of TS 3.3.3.6 Action d, for returning radiation monitors to operability. None of the corrective actions for these events could have prevented this event due to the multiple equipment failures coupled with the time requit ad to calibrate this channel.

1. Inoperable Main steam Line Radiation Monitors Special Report 88-03: All Unit I and Unit 2 main steam line radiation monitors were declared inoperable as a result of detector misalignment due to an inadequate installation procedure.

Special Report 88-02: Main steam line radiation monitor 1RM-71 was inoperable for more than seven days due to a component failure on a printed circuit board.

Special Report 86-02: Main steam line radiation monitor 1RM-71 was inoperable for more than seven days due to a failed power supply circuit board and log rate circuit board.

2. Inoperable Plant Vent Radiation Monitors Special Report 88-07: Plant vent radiation monitor 1RM-29 was inoperable for more than seven days due to inadequate planning.

Special Report 88-01: Plant vent radiation monitor IRM-29 was inoperable for more than seven days due to monitor failure resulting from moisture intrusion in the detector shield.

Special Report 87-04: Plant vent radiation monitor 1RM-29 was inoperable for more than seven days due to failed components in the instrument drawer.

Special Report 86-03: Plant vent radiation monitor 2RM-29 was inoperable for more than seven days due to a failed detector.

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