~ Ac CEMRATED > BUTION DEMON ATION SYSTEM

REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR: 8811080209 DOC. DATE: 88/11/02 - NOTARIZED: NOFACIL:50-323 Diablo Canyon Nuclear Power Plant, Unit 2, Pacific Ga

AUTH.NAME AUTHOR AFFILIATIONSOKOLSKY,D. Pacific Gas & Electric Co.SHIFFER,J.D. Pacific Gas & Electric Co.

RECIP.NAME RECIPIENT AFFILIATION

DOCKET05000323

SUBJECT: LER 88-011-00:on 881003,fuel handling bldg ventilation sysshift to iodine removal mode due to radiation fluctuations.W/8 ltr.

DISTRIBUTION CODE: IE22D COPIES RECEIVED:LTR ( ENCL f SIZE:TITLE: 50.73 Licensee Event Report (LER), Incident Rpt, etc.NOTES:

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On October 3, 1988, at 0308 PDT, and on October 19, 1988 at 1812 PDT, with the Unitin a refueling outage (all fuel removed from the reactor vessel), fuel handlingbuilding (FHB) radiation monitor 2-RM-58 exceeded the high alarm setpoint andcaused the FHB ventilation system to shift to the 'iodine removal mode. Afterobserving that radiation levels were below the high alarm setpoint (7.5 mR/hr), theFHB,ventilation system was returned to the normal mode of operation following theOctober 3 occurrence. Following the October 19 occurrence, a new alarm setpoint of10 mR/hr was established and the FHB ventilation system was returned to the normalmode of operation. The Technical Specifications require the setpoint to be lessthan 15 mR/hr.

The 4-hour nonemergency report required by 10 CFR 50.72 was completed on October 3,1988 at 0415 PDT for the first occurrence and on October'19 at 1916 PDT for thesecond occurrence.

The increase in background. radiation is caused by the higher background readingsfrom the recent off-load of the Unit 2 reactor fuel combined with the fact thatspent fuel pool (SFP) demineralizer and pool skimmer were not operatedcontinuously. This caused background radiation fluctuations to increase and exceedthe overly conservative low setting of the high alarm setpoint. Applicableprocedures will be revised to require operation of the SFP recirculationdemineralizer and pool skimmer to reduce background radiation levels for fuelhandling operations.

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At the time of the event,. all fuel had been removed from the reactor vesseland placed in the spent -fuel pool (refueling outage). Fuel inspectionactivities were being performed.

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A. Event:

First Occurrence:

On October 3, 1988 at 0308 PDT the Unit 2 Fuel Handling Building (FHB)Radiation Monitor (VG)(RI)(2-RM-58) exceeded the high radiation alarmsetpoint and.caused the FHB Ventilation System (VG) to shift to theiodine removal mode,. This mode change constitutes actuation of an .

engineered safety feature (ESF).

,The background radiation level in the vicinity of the spent fuel pool(SFP) had increased to an average of about 5 mR/hr following -the recentstorage of cycle 2 spent fuel. This background radiation level is nearthe high alarm setpoint. Random background radiation fluctuations of. 2

to 3 mR/hr occasionally occur. Therefore, the event is, believed to havebeen caused by background radiation fluctuations sufficient to reach thehigh alarm setpoint for 2-RM-58.

Following verification of expected radiation level readings, the FHB

radiation monitor alarm was reset and the FHB ventilation system wasreturned to its normal mode of operation.

The FHB ventilation system was placed in the iodine removal mode at 0516,at the request of the shift supervisor. Additional high radiation alarmswere activated at 0611 PDT, 0701 PDT and 1125 PDT.

The subsequent alarms were not considered ESF actuations because theventilation system was already in its ESF mode of operation. Additionalsurveys were made which verified that dose rates indicated by 2-RM-58were 'accurate and correct. The FHB ventilation system was subsequentlyreturned to the normal mode of operation.

The 4-hour n'onemergency report required by 10 CFR 50.72 was completed at0415 PDT.

Second Occurrence:

On October 19, 1988 at 1812 PDT the Unit 2 FHB Radiation Monitor(2-RM-58) exceeded the high alarm setpoint and caused the FHB Venti lati'onSystem to transfer to the iodine removal mode. Following verification

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that the radiation level reading was below the high alarm setpoint, thealarm was reset. However, the ventilation system was left in the iodineremoval mode until'2334 PDT at which time it was returned to the normalmode of operation following the recalibration of the high alarm setpointto the recently approved 10 mR/hr value.

The 4-hour nonemergency report required, by 10 CFR 50.72 was. completed at1916 PDT.

B. Inoperable structures, components or systems that contributed to theevent:

None

C. Dates and approximate times for ma)or occurrences:

First Occurrenc'e:

1. October 3, 1988 at 0308 PDT:

2. October 3, 1988 at 0415 PDT:

3. October 3, 1988. at 0516 PDT:

Event and discovery date. FHBventilation system returned to thenormal operating mode.

4-hour nonemergency notificationrequired by 10 CFR 50.72 completed.

Placed FHB ventilation system in theiodine removal mode.

4. October 3, 1988 at 0611 PDT: FHB high radiation alarm

5. October 3, 1988 at 0701 PDT: FHB high radiation alarm

6. October 3, 1988 at 1125 PDT: FHB high radiation, alarm

Second Occurrence:

1. October 19, 1988 at 1812 PDT: FHB high radiation alarm andventilation system transfer toiodine removal mode.

2. October 19, 1988 at. 1814 PDT: FHB high radiation alarm was reset.

3. October 19, 1988 at 1916 PDT:

4. October 19, 1988 at 2334 PDT:

4-hour nonemergency notification per10 CFR 50.72 completed.

FHB high radiation alarm setpointwas reset to 10 mR/hr and the

.ventilation system returned to thenormal operating mode.

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D. Other systems or secondary functions affected:

None

E. Method of discovery:

The event was immediately known to the control room operator by receiptof an alarm in the control room.

F. Operator actions:

Following determination that the radiation level was below the high alarmsetpoint, the operator reset the alarm. The ventilation system wasreturned to the normal operating mode.

G. Safety system responses:

The FHB ventilation system shifted to the iodine removal mode as designedwhen the radiation monitor exceeded the high alarm setpoint.

fEvnA. Immediate cause:

Background radiation fluctuations exceeded the high alarm setpoint-of 7.5mR/hr, which caused the FHB ventilation system to shift to the iodineremoval mode.

B. Root cause:

The root cause of this event was an overly conservative high alarm/trip(ESF actuation) setpoint for 2-RM-58.

Technical Specification Table 3.3-6 requires that the fuel handlingbuilding high alarm/trip setpoint be maintained less than or equal to 15mR/hr. To ensure that the combined instrument and calibration errorscould not result in the high alarm/trip setpoint exceeding the TechnicalSpecification limit, a conservative methodology of arithmetic summationof instrument and calibration errors was used to establish and verify thealert setpoint of 5 mR/hr and the high alarm/trip (ESF actuation)setpoint of 7.5 mR/hr.

General Atomic, the radiation monitor manufacturer, was contacted afterthe October 3 occurrence. The manufacturer indicated that the instrumentand calibration errors were independent variables, and could be combinedby the Root Mean Squared method, rather than simple arithmeticsummation. Instrumentation and Controls (IKC) Engineering evaluated thisrevised method of combing errors and concluded that the alert setpointcould be increased from 5 to 6.5 mR/hr and the high alarm/ESF actuationsetpoint could be increased from 7.5 to 10 mR/hr.

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Exceeding the high alarm setpoint on 2-RH-58 is due in part to the higherbackground reading from the recent off-load of the Unit 2, cycle 2

reactor core. This higher background was due to the fact that the SFP.

recirculation demineralizer and pool skimmer were not operatedcontinuously.

t«. ~lThe FHB radiation levels were verified to be'orrectly portrayed by themonitor. The FHB radiation monitor reading increased to its high alarmsetpoi nt and automatically transferred the FHB ventilation system to theiodine .removal mode, per design. The automatic transfer of the FHB system tothe iodine removal mode is a conservative response. Therefore, there were no

adverse safety consequences from this event, and the health and safety ofthe'eneralpublic was not jeopardized.

V. rr iv

A. Immediate corrective actions:

Following the October 3 occurrence, the SFP recirculation demineralizerwas placed in service, and the FHB ventilation system was placed in theiodine removal mode. A decrease in background radiation levels was

observed. Hhen the background radiation level decreased, the FHB

ventilation system was subsequently returned to its normal mode ofoperation and the SFP recirculation demineralizer was secured.

The alert alarm setpoint for 2-RH-58 was increased from 5 to 6.5 mR/hr,and the high alarm and ESF actuation setpoint from 7.5 to 10 mR/hr.

B. Corrective actions to prevent recurrence:

IhC Engineering will evaluate system requirements and investigatemodification of the RH-58 actuation circuitry to provide a time delay forESF actuations.

The operating procedures concerning the use of the SFP recirculationsystem demineralizer and pool skimmer will be revised to requireoperation of the SFP recirculation demineralizer and pool skimmer to"reduce background radiation levels for fuel handling operations.

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VI.

A. Failed components:

None

B. Previous LERs on similar events:

LER 1-88-011-00 was issued on June 9, 1988 regarding a similar event inUnit 1. The corrective action of LER 1-88-011-00.required aninvestigation to determine the acceptability of increasing the high.radiation alarm setpoint. This investigation determined that revision ofthe setpoint was not acceptable „at that time based on the radiationmonitor manufacturer's original recommendation to use the conservativemethodology of arithmetic summation for combining instrument andcalibration errors. Corrective action from the previous event could nothave prevented the occurrence of this event. Following the October 3occurrence, the radiation monitor manufacturer was contacted, and it wassubsequently determined that the alert and high alarm setpoints could beincreased by revising the methodology of combining instrument andcalibration errors. Authorization to change the setpoint was notfinalized, however, until after the October 19 occurrence. ,LER1-88-011-00 will be revised to reflect the implementation of the changeto the alert and high alarm setpoints for 1-RH-58.

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Pacific Gas and Electric Company 77 Beate Street

San Francisco, CA 94106

415/972 7000TWX910 372 6587

James 0. Shifter

Vice President

Nuclear Power Generation

November 2, 1988

PGhE Letter No. DCL-88-263

U.S. Nuclear Regulatory CommissionAttn: Document Control DeskHashington, D.C. 20555

Re: Docket No. 50-323, OL-DPR-82Diablo Canyon Unit 2Licensee Event Report 2-88-011-00Fuel Handling Building Ventilation System Shift to IodineRemoval Mode Nhen Radiation Monitor 2-RM-58 Exceeded the HighAlarm Setpoint Due to Background Radiation Fluctuations

Gentlemen:

Pursuant to 10 CFR 50.73(a)(2)(iv), PGhE is submitting the enclosedlicensee Event Report concerning the shifting of the fuel handlingbuilding ventilation system to the iodine removal mode whenradiation monitor 2-RM-58 exceeded the high alarm setpoint of 7.5mR/hr.

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

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

Sincerely,

3. D. SHIFFE

cc: J. B. MartinM. M. MendoncaP. P. NarbutB. NortonH. RoodB. H. VoglerCPUCDiablo Distribution

Enclosure

DC1-88-TI-N059

2388S/0064K/DY/2179