ML17305B169

Suppl to Special Rept 2-SR-88-009:on 881206,radiation Monitoring Unit Inoperable for More than 72 H

ML17305B169
Person / Time
Site:	Palo Verde
Issue date:	10/27/1990
From:	James M. Levine ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
192-00701-JML-T, 192-701-JML-T, 2-SR-88-009, 2-SR-88-9, NUDOCS 9011070244
Download: ML17305B169 (8)

Text

ACCELERATED IQTRIBUTION DEMONSATION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9011070244 DOC.DATE: 90/10/27 NOTARIZED: NO DOCKET 'N FACIL:STN-50-529 Palo Verde Nuclear Station, Unit 2, Arizona Publi 05000529 AUTH.NAME AUTHOR AFFILIATION LEVINE,J.M.

Arizona Public Service Co.

(formerly Arizona Nuclear Power RECIP.NAME RECIPIENT A'FFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

Suppl to Sepcial Rept 2-SR-88-009:on 881206,radiation monitoring unit inoperable for more than 72 h.

DISTRIBUTION CODE:

IE22D COPIES RECEIVED:LTR ENCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER), Incident Rpt, etc.

NOTES:Standardized plant.

D S

05000529 RECIPIENT ID'ODE/NAME PD5 LA PETERSON,S.

INTERNAL: ACNW AEOD/DOA AEOD/ROAB/DSP NRR/DET/EMEB 7E NRR/DLPQ/LPEB10 NRR/DST/SELB 8D NRR/DST/SPLB8D1

~REG F'I~li1~~0+

RGN5 FILE 01 EXTERNAL: EG&G BRYCE,J.H NRC PDR NSIC MURPHY,G.A NOTES COPIES LTTR ENCL 1

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1 RECIPIENT ID CODE/NAME PD5 PD TRAMMELL,C.

ACRS AEOD/DSP/TPAB NRR/DET/ECMB 9H NRR/DLPQ/LHFB11 NRR/DREP/PRPB11 NRR/DST/SICB 7E NRR/DST/SRXB 8E RES/DSIR/EIB L ST LOBBY WARD NSIC MAYS,G NUDOCS FULL TXT COPIES LTTR ENCL 1

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NOTE TO ALL"RIDS" RECIPIENTS:

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PLEASE HELP US TO REDUCE KVASTE! CONTACT THE DOCUMENT CONTROL DESK, ROOM P 1-37 (EXT. 20079) TO ELIMINATEYOUR NAME FROM DISTRIBUTION LISTS FOR DOCUMENTS YOU DON'T NEED!

TOTAL NUMBER OF COPIES REQUIRED:

LTTR 34 ENCL 34

'I h

I t

JAMES M. LEVINE VICE PRESIDENT NUCLEAR PRODUCTION Arizona Public Service Company PALO VERDE NUCLEAR GENERATING STATION P.O. BOX 52034

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PHOENIX, ARIZONA85072-2034 192-00701-JML/TRB/SBJ October 27, 1990 U.

ST Nuclear Regulatory Commission Attention: Document Control Desk Mail Station:

Pl-37 Washington, DC 20555

Subject:

Palo Verde Nuclear Generating Station (PVNGS)

Unit 2 Docket No.

STN 50-529 (License No. NPF-51)

Supplement to Special Report 2-SR-88-009 File'0-020-404, Attached please find Supplement Number 5 to Special Report 2-SR-88-009 prepared and submitted pursuant to Technical Specifications 3.3.3.8 and 6.9.2.

This report is submitted to update the schedule for completing the development of the final design change.

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

Very truly yours, JML/TRB/SBJ/dmn Attachment CC:

W. F.

J.

B.

D. H.

A. C.

A. L.

Conway Martin Coe Gehr Gutterman (all with attachm'ent)

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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 Supplement Number 5 to Special Report 2-SR-88-009 This Special Report is submitted in accordance with Technical Specifications 3.3.3.8 ACTION 42(b) and 6.9.2 for an event in which the Condenser Vacuum Pump/Gland Seal Exhaust High Range Effluent Monitor (RU-142) and Plant Vent High Range Effluent Monitor (RU-144) were 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-hour limit for operability was exceeded at approximately 0700 MST and 0630 MST respectively on December 9,

1988.

At approximately 0630 MST on December 6, 1988, with Palo Verde Unit 2 in Mode 1

(POWER OPERATION) at approximately 100 percent power, the Condenser Vacuum Pump/Gland Seal Exhaust low and high range monitors (RU-141 and RU-142) were declared inoperable to perform corrective maintenance on the low range monitor.

At approximately 0700 MST-on December 6,

1988 the Plant Vent Monitors (RU-143 and RU-144) were also declared inoperable to perform corrective maintenance on the low range monitor.

Both low range monitors were exhibiting intermittent spiking; however, this condition did not cause the monitors to be inoperable.

In each case the monitors work as a pair with RU-141 and RU-143 as the low range monitors and RU-142 and RU-144 as the high range monitors.

Normal configuration consists of the low range monitors operating with the high range monitors in standby.

When the low range monitors reach a predetermined

setpoint, the high range monitors start and the low range monitor goes to standby.

The high range monitors are provided for tracking radioactive effluents during postulated accident'cenarios.

The high range monitors must be declared inoperable when, the low range monitors are 'inoperable.

Pursuant to Technical Specification 3.3,3 '

ACTION 37, the Preplanned Alternate Sampling Program (PASP) was initiated at approximately 0712 MST and 0645 MST respectively on December 6, 1988.

The PASP continued until the radiation monitors were returned to service.

RU-143 and RU-144 were returned to service at 1117 MST on March 22, 1989.

RU-141 and RU-142 were returned to service at 0935 MST on June 23, 1989.

The term "spiking" as used in this report is defined as an apparent rise in current level which is causing the radiation level 'to appear to increase although no actual rise in radiation exists.

APS has been experiencing these spikes since licensing of the units.

In each previous case, actions were taken to troubleshoot and correct the problems as they occurred.

Additionally, overall recommendations were made, and plant changes instituted on the basis of the spiking being caused by a grounding problem.

When incorporated into the units, these plant changes have not fully resolved the spiking problem.

1 l$

" Special Report 2-SR-88-009-05 Page 2

On December 6, 1988, a decision was made to leave RU-141 and RU-143 inoperable for an extensive testing program to determine the root cause of the spiking.

The testing program was initiated on December 20, 1988.

The low range monitors RU-141, RU-143, and RU-145 (Fuel Building Ventilation System Low Range radiation monitor) use beta scintillation detectors to monitor the process and generate an electrical pulse that is proportional to the particular type of radiation being monitored, i.e. particulate, gas,'or iodine.

The detector's outer housing is metal and is connected to plant ground by its mounting arrangements.

The detector's preamplifier is referenced to an independent Radiation Monitoring System (RMS) instrument ground bus rather than plant ground.

Due to the potential differences between the detector preamplifier's signal ground and the detector's grounded outer housing, parasitic capacitance coupling exists between the preamplifier's signal ground and the detector's grounded outer housing.

Noise on the plant ground is able to couple into the detector's preamplifier through these parasitic capacitance paths.

These stray capacitances provide a feedback path from output to input of the preamplifier.

Thus, noise occasionally couples into the preamplifier and forces the preamplifier into oscillation due to the capacitive feedback path.

This can result in the detector generating spurious output pulses of sufficient magnitude that the amp/discriminator circuit in the microcomputer treats them as valid signals resulting in the generation of spurious high readings.

These spurious output pulses will be prevented by eliminating the capacitive feedback path.

This will be accomplished by isolating the detector's housing from plant ground and connecting it to the preamplifier's signal ground.

This eliminates the capacitance feedback path.

A temporary modification has been implemented on radiation detectors RU-141, RU-143 and RU-145 in Units 1, 2, and 3 in order to eliminate the capacitive feedback path.

The radiation detectors have not experienced any spiking since completion of the temporary modification.

Only radiation monitors RU-141, RU-

143, and RU-145 have been modified because beta scintillation detectors are significantly more sensitive than the detectors used in other radiation monitors.

A design change is being prepared that will enhance the circuit design and update plant drawings.

Development of the design change is expected to be completed by November 30, 1990.

Circuit changes are expected to be implemented in Units 1, 2,

and 3 within 90 days of materials receipt.

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