ML17304A343

Suppl 1 to Special Rept 2-SR-87-024:on 870918,72 H Limit for Inoperability Exceeded for high-range Noble Gas Monitor. Caused by Poor Design for Check Source Circuitry.Design Change Prepared for Implementation to Eliminate Circuit

ML17304A343
Person / Time
Site:	Palo Verde
Issue date:	08/10/1988
From:	Haynes J ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
192-00399-JGH-T, 192-399-JGH-T, 2-SR-87-024, 2-SR-87-24, NUDOCS 8808220003
Download: ML17304A343 (8)

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ACCESSION NBR: 8808220003 DOC. DATE: 88/08/10 NOTARIZED: NO DOCKET g FACIL: STN-50-529 Palo Verde Nuclear Stations Unit 2i Arizona Publi 05000529 AUTH. NAME AUTHOR AFFILIATION HAYNES'. G. Arizona Nuclear Power Prospect (formerly Arizona Public Serv RECIP. NAME RECIPIENT AFFILI*TION Document Control Branch (Document Control Desk>

SUBJECT:

Supp 1 1 to Special Rept 2-SR-87-024-01: on 870915'adiation monitoring unit inoperable for greatter than 72 h.

DISTRIBUTION CODE: IE22D COPIES RECEIVED: LTR f ENCL I SIZE: 9 TITLE: 50. 73 Licensee Event Report (LER)i Incident Rpti etc.

NOTES: Standardized plant. 05000529 RECIPIENT COP I ES RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 LA 1 1 PD5 PD 1 1 LICITRAiE 1 DAVIS> M 1 1 INTERNAL: ACRS MICHELSON 1 1 ACRS MOELLER 2 2 ACRS WYLIE 1 1 AEOD/DOA 1 1 AEOD/DSP/NAS 1 AEOD/DSP/ROAB 2 2 AEOD/DSP/TPAB 1 1 ARM/DCTS/DAB 1 1 DEDRO 1 1 NRR/DEST/ADS 7E 1 0

NRR/DEST/CEB 8H 1 NRR/DEST/ESB 8D 1 NRR/DEST/ I CSB 7 1 NRR/DEST/MEB 9H 1 1 NRR/DEST/MTB 9H 1 1 NRR/DEST/PSB 8D 1 1 NRR/DEBT/RSB 8E 1 NRR/DEST/SGB 8D 1 1 NRR/DLPQ/HFB 10 1 ~

1 NRR/DLPQ/QAB 10 1 1 NRR/DOEA/EAB 11 1 1 NRR/DREP/R*B 10 1 1 NRR/DREP/RPB 10 2 2 NRR/DRIS/SIB 9A 1 NUDOCS-ABSTRACT 1 1 G 02 1 1 RES TELFORDi J 1 1 RES/DSIR DEPY 1 1 RES/DSIR/EIB 1 1 RGN5 FILE 01 1 1 EXTERNAL: EG~~G WILLIAMS' FORD BLDG HOYLE A 1 1

H ST LOBBY W*RD 1 1 LPDR 1 NRC PDR 1 1 NSIC HARRIS' 1 1 NSIC MAYST G 1 1 NOTES: 1 1 TOT*L NUMBER OF COPIES REQUIRED: LTTR 48 ENCL 47

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Arizona Nuclear Power Project P,O. BOX 52034 ~ PHOENIX, ARIZONA 85072-2034 192-00399-JGH/TDS/DAJ August 10, 1988 U.S. Nuclear Regulatory Commission NRC Document Control Desk Washington, D.C. 20555

Subject:

Palo Verde Nuclear Generating Station Unit 2 Docket No. STN 50-529 (License NPF-51)

Supplement to Special Report 2-SR-87-024 File: 88-020-404 Attached please find Supplement 1 to Special Report 2-SR-87-024 prepared and submitted pursuant to Technical Specification 3.3.3.8 and 6.9.2. This report is submitted to provide updated information from the previous submittal.

If you have any questions, please contact T. D. Shriver, Compliance Manager at (602) 393-2521.

Very truly yours, J. G. Haynes Vice President Nuclear Production JGH/TDS/DAJ/kj Attachment cc: D. B. Karner (all w/a)

E. E. Van Brunt, Jr.

T. J. Polich E. A. Licitra A. C. Gehr INPO Records Center SSOS1P SSOS22pp Ogppp529 poOC~ pnu 6

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PALO VERDE NUCLEAR GENERATING STATION RADIATION MONITORING UNIT INOPERABLE FOR GREATER THAN 72 HOURS License No. NPF-51 Docket No. STN 50-529 Special Report No. 2-SR-87-024-01 Supplement No. 1 to this Special Report is submitted in accordance with Technical Specification (T.S.) 3.3.3.8 ACTION 42 (b) and 6.9.2, to provide additional information for an event in which a high range noble gas monitor (RU-146) was inoperable for greater than '72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> limit for inoperability was exceeded at approximately 0927 MST on September 18, 1987.

At approximately 0927 MST on September 15, 1987 with Palo Verde Unit 2 in Mode 1 (POWER OPERATION) at 100 percent power, the Fuel Building "B" Vent Exhaust Low and High Range Monitors (RU-145/146) were declared inoperable and placed in bypass for problems with recurrent spiking due to inadvertent initiation of the automatic check source mechanism, resulting in conservatively false background radiation readings on RU-145.

Monitors RU-145 and RU-146 monitor the fuel building ventilation exhaust for release of activity. Monitor RU-145 performs the safety function of isolating the normal ventilation system by initiating Fuel Building Essential Ventilation Actuation Signal (FBEVAS) on a HIGH-HIGH activity alarm. Monitors RU-145 and RU-146 work as a pair, with RU-145 being the low range monitor and RU-146 being the high range monitor. Normal configuration consists of RU-145 operating and RU-146 in standby. When RU-145 reaches a predetermined setpoint, RU-146 starts and RU-145 goes to standby. RU-145 and RU-146 are required to be operable in Modes 1, 2, 3 and 4 or when irradiated fuel is in the fuel storage pool. Since RU-145 and RU-146 work in tandem, RU-146 must be declared inoperable if RU-145 is placed in an inoperable status.

Flowrate estimates were initiated at least once every four hours, grab samples at least once every twelve hours, and particulate and iodine sampling on a continuous basis, in accordance with T.S. 3.3.3.8 ACTIONS 36, 37 and 40.

Provisions were also made to ensure compliance with T.S. 3.3.3.8 ACTION 41 and 3.9. 12 ACTION (b) .

At approximately 1950 MST on September 17, 1987, the particulate and iodine samplers, flowrate monitor and sample flowrate measuring device of the subject monitors were determined to be unaffected by the voltage spiking problem.

These functions were returned to service at approximately 2035 MST on September 18, 1987, at which time T.S. 3.3.3.8 ACTIONS 36 and 40 were exited.

The noble gas monitor function for both monitors remained inoperable under the provisions of T.S. 3.3.3.8 ACTION 37, 41, 42 and 3.9. 12 ACTION (b), as noted above.

At approximately 0915 MST on September 24, 1987, all functions for RU-145/146 were declared inoperable to permit troubleshooting and engineering evaluation under an approved wor k document, at which time the compensatory measures specified by T.S. 3.3.3.8, ACTIONS 36 and 40 were reinstated. Troubleshooting and engineering evaluation continued through November 6, 1987, at which time it was determined that the problem appeared to be a resistor in the check source circuitry which had too small of a value. The resistor was replaced

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Supplement to Special Report 1-SR-87-024, Page 2 and additional maintenance was performed to replace the power supply assembly, the interface board for the skid-mounted indication and control (SNIC) unit and the remote indication and control (RIC) unit, and the sample flow control valve. These work items were incidental to the corrective action for the problem described above.

After completion of the above maintenance activities, RU-145 and RU-146 were satisfactorily tested in accordance with surveillance testing requirements, and by performance of a channel check. The monitors were restored to operable status at approximately 1507 HST on December 3, 1987, having been inoperable for approximately 79 days.

Continuing engineering investigation determined that the root cause of the problem was a poor design for the check source circuitry. Spurious signals would cause inadvertent actuations of the automatic check source. In order to correct this problem a design change has been prepared for implementation to eliminate the check source ground loop circuit and replace it with a more reliable configuration.