ML20059D114

Intervenor Exhibit I-MFP-144,consisting of LER 1-92-005-01, Re Docket 50-275,dtd 920720

ML20059D114
Person / Time
Site:	Diablo Canyon
Issue date:	08/21/1993
From:	Rueger G PACIFIC GAS & ELECTRIC CO.
To:
References
OLA-2-I-MFP-144, NUDOCS 9401070011
Download: ML20059D114 (6)

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g.hg f July 20, 1992 93 OCT 28 P5 50 PG&E Letter No. DCL-92-162 ,

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U.S. Nuclear Regulatory Commission l ATTN: Document Control Desk Washington, D.C. 20555 A' b Re: Docket No. 50-275, OL-DPR-80 Diablo Canyon Unit 1 Licensee Event Report 1-92-005-01 Containment Ventilation Isolation Due to Spurious High Radiation Signal Gentlemen:

Pursuant to 10 CFR 50.73(a)(2)(iv) and item 19 of Supplement I to NUREG-1022, PGLE is submitting the enclosed revision to Licensee Event Report (LER) 1-92-005-00 regarding a Unit I containment ventilation isolation due to a high radiation signal on Radiation Monitor RM-14B.

This revision is being submitted to report the root cause and corrective actions for this event. Revision bars are included to indicate the changes.

Sincerely, sM M y- ---

Grego y M. Rueger ,

cc: Ann P. Hodgdon John B. Martin Philip J. Morrill Harry Rood CPUC Diablo Distribution INPO DCl-92-TI-N020 Enclosure -

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LICENSEE EVENT REPORT (LER) t DIABLO CANYON UNIT 1 0l5l0l0l0l2l7l5 1l 'l 5" s ul C0'lTAINMENT VENTILATION ISOLATION DUE TO SPURinUS HIGH RADIATION SIGNAL EvtmT Datt ai LaR hl>AS ER 181 REPORT DATE t7a OYMta fac1LITIES IMv0LvtD (5)

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RAYMOND L. THIERRY, SENIOR REGULATORY COMPLIANCE ENGINEER '( " '

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On April 28, 1992, at 1249 PDT with Unit 1 in Mode 1 (Power Operation) at 100 percent power, a containment ventilation isolation (CVI) actuation occurred when the output signal of Radiation Monitor RM-14B exceeded its alarm setpoint.

This event constitutes an Engineered Safety Feature (ESF) actuation. A four-hour, non-emergency report was made to the NRC in accordance with 10 CFR 50.72 (b)(2)(ii) on April 28 at 1429 PDT.

After verifying that no high radiation conditions existed and that RM-14B responded normally, the control room operators reset the CVI logic and returned the containment

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ventilation system to its normal operating mode.

The root cause of this event was a loose connector on the test box used during maintenance on RM-28B. The loose connector resulted in generation of electronic noise in the circuitry of RM-14B. The output of RM-14B exceeded its alarm setpoint and ultimately led to the CVI.

The corrective actions to prevent recurrence include: (1) issuance of an I&C maintenance bulletin that discusses the event and precautions to take during similar

! maintenance activities; (2) the content of the I&C maintenance bulletin will be included i

in the 11C quarterly maintenance seminar; (3) discussions on radiation monitors will be held in a tailboard regarding precautions to take during similar maintenance activities; .

and (4) 1&C technicians will make a one-time visual inspection of other test boxes to )

identify similar connector problems, f

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l LICENSEE EVENT REPORT (LER) TEXT CONTINUATION b . m a ,, - m m.o --. m m.

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1. Plant Conditions Unit I was in Mode 1 (Power Operation) at 100 percent power.

II. Description of Event A. Event

Description:

On April 28,1992, at 1249 PDT,. a containment ventilation isolation .. <

(CVI) actuation occurred. This event constitutes an Engineered Safety Feature (ESF) actuation. A four-hour, non-emergency report was'made to the NRC in accordance with 10 CFR 50.72(b)(2)(ii) on April 28 at '

1429 PDT.

The output signal of Radiation Monitor (RM) 14B (IL)(MON) (plant vent. i radioactive gas monitor) exceeded its alarm setpoint, causing the CVI actuation. The redundant monitor did not detect any elevated activity ,

level, and therefore the response of RM-14B was considered spurious.  !

After verifying that no high radiation condition existed, the control room operators reset the CVI logic and returned the containment ventilation system to its normal operating mode. i During maintenance activities on Unit 2, the I&C technicians

! discovered a loose connector in the test box that was used on the-l Unit 1 RM-28B at the time of the Unit 1 evant. The loose connector i resulted in generation of electronic noise in the circuitry of RM-14B, since RM-28B is in close proximity to RM-14B. The electronic noise caused the output of RM-14B to exceed its alarm setpoint and ultimately led to the CVI.

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

i Event:

None. ,

l C. Dates and Approximate Times for Major Occurrences:

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1. April 28, 1992; at 1249 PDT: Event / Discovery date - i RM-148 spurious high l radiation alarm caused the i CVI actuation.  !

2. April 28, 1992; at 1429 PDT: A four-hour, non-emergency ,

report was made to the NRC i in'accordance with 10 CFR' l l 50.72(b)(2)(ii).

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I D. Other Systems or Secondary Functions Affected:

None.

E. Method of Discovery:

The event was immediately apparent to plant operators due to alarms and indications received in the control room.

F. Operators Actions:

The operators determined that the CVI was due to a' spurious high l radiation alarm because the redundant monitor (RM-14A) did not detect any elevated activity level. After serifying that no high radiation l conditions existed and that RM-14B responded normally, the control l room operators reset the CVI logic and restored the containment i ventilation system to its normal mode of operation.

G. Safety System Responses:

All containment ventilation isolation valves (NH)(V) closed as designed.

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

The immediate cause of the CVI was a spurious high radiation alarm from RM-14B. -

B. Root Cause:

The root cause of this event was a loose connector on the test box used during maintenance on RM-28B. The loose connector resulted in generation of electronic noise in the circuitry of RM-14B. The output of RM-14B exceeded its alarm setpoint and ultimately led to the CV1.

IV. Analysis of the Event A CVI is a conservative actuation, regardless of plant conditions. If an actual high radiation condition had occurred during the event, the containment ventilation. system would have been ready to perform its accident prevention function. Consequently, this event did not adversely affect the health and safety of the public.

53275/S5K

• LICENSEE EVENT REPORT (LER) TEXT CONTINUATION FACILIT, h4M( (3) DOCE(1 N W8(S (2) l Lf8 NUM9(R <6) S&G( (3) j I W" N 81E f

DIABLO CANYON UNIT 1 0l5l0l0l0l2l7l5 92 -

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0l1 4I"l5 1( 1 on V. Corrective Actions A. Immediate Corrective Actions:

1. After verifying that no high radiation conditions existed, the control room operators reset the CVI logic and restored the containment ventilation system to its normal mode of _ operation.

2. After discovering the loose connector, the I&C technicians repaired the test box.

B. Corrective Actions to Prevent Recurrence:

1. An I&C maintenance bulletin will be issued to discuss the event and precautions to take during similar maintenance activities.

2. The event and precautions discussed in the maintenance bulletin will be included in the 1&C quarterly maintenance training seminar.

3. Discussions will be held in a tailboard with appropriate electrical maintenance personnel on precautions to take during similar maintenance activities on radiation monitors.

4. I&C technicians will make a visual inspection of other test boxes to identify similar connector problems.

VI. Additional Information A. Failed Components:

None.

B. Previous LERs on Similar Problems:

Similar spurious system initiations were reported in a number of LERs, including LER l-86-007-01, LER l-86-014-01, LER l-86-015-01, LER l-87-003-01, 1-88-005, and 1-91-006. Although these previous LERs i discuss various spurious actuations, none of the corrective actions l would have precluded recurrence of the CVI reported in LER l-92-005.

1. As discussed in PG&E letter DCL-89-254, dated October 2, 1989, I

" Noise Reduction Task Force Final Report LER l-86-007-01, LER  !

l-86-014-01, LER l-8E 015-01, and LER l-87-003-01," power transients affecting CVI-related radiation monitors have caused several CVIs. Reducing CVis caused by power transients is being addressed by several corrective actions: (1) training to reduce power transients caused by human error; (2) adding CVI bypass 58275/85K l

LICENSEE EVENT REPORT (LER) TEXT CONTINUATION

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0l1 5l"l5 TEET 07) switches to allow disabling of the CVI function during radiation monitor maintenance; and (3) initiating a Radiation Monitor System upgrade program to replace existing radiation monitors with equipment that is less sensitive to electrical noise. The time delay circuitry modification already implemented reduces spurious CVIs caused by noise on the signal input; however, the output relays of the monitors are still sensitive to transients on their power supply. These corrective actions would not have prevented the current LER.

2. LER l-88-005, " Containment Ventilation isolation Due to Electronic Noise and Late Issuance of a 10 CFR 50.72 Required Report Due to Inadequate Guidance." This LER reported a CVI actuation signal that was generated by RM-14A due to an electronic noise generated when an I&C technician eneraized RM-13 during maintenance. The late reporting was due to inadequate guidance contained in an administrative procedure regarding exemptions to reporting requirements. The time delay circuitry change installed in radiation monitors that actuate the CVI system and the revision of the procedure on reporting ESF actuations would not have prevented the current LER.

3. LER l-91-006, " Actuation of Containment Ventilation Isolation Due to a Spurious High Radiation Alarm Resulting From Radio frequency Energy Generated by a faulted Motor." This LER reported a CVI due to a spurious high radiation alarm from containment air particulate monitor RM-ll. The root cause for the spurious high radiation alarm and resulting CVI was due to radio frequency interference (RFI) produced when the RM-Il sample pump seized. After the pump seized, the pump motor faulted and arced over to a bus ground. The arcing produced sufficient RFI to induce the spurious high radiation signal.

The design change to provide thermal overload protective circuitry for the sample pump motors and the upgrade of the radiation monitoring system to reduce sensitivity to noise would not have prevented the current LER.

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