ML17305A928

Suppl 4 to Special Rept 2-SR-88-009:on 881206,condenser Vacuum Pump/Gland Seal Exhaust Low & High Range Monitors Declared Inoperable.Capacitive Feedback Path Will Be Eliminated to Prevent Spurious Output Pulses

ML17305A928
Person / Time
Site:	Palo Verde
Issue date:	07/11/1990
From:	James M. Levine ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
192-00674-JML-T, 192-674-JML-T, 2-SR-88-009, 2-SR-88-9, NUDOCS 9007170123
Download: ML17305A928 (7)

Text

ACCELERATED DISTRIBUTION DEMONSTRATION SYSTEM REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS)

ACCESSION NBR:9007170123 DOC DATE: 90/07/11 NOTARIZED: NO DOCKET FACIL:STN-50-529 Palo Verde Nuclear Station, Unit 2, Arizona Publi 05000529 1T AUTH. NAME AUTHOR AFFILIATION LEVINE,J.M. Arizona Public Service Co. (formerly Arizona Nuclear Power RECIP.NAME RECIPIENT AFFILIATION Document Control Branch (Document Control Desk)

SUBJECT:

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

DISTRIBUTION CODE: IE22D D COPIES- RECEIVED:LTR r ENCL SIZE:

TITLE: 50.73/50.9 Licensee Event Report (LER),incident Rpt, et NOTES:Standardized plant. 05000529 RECIPIENT RECIPIENT COPIES ID CODE/NAME LTTR ENCL ID CODE/NAME LTTR ENCL PD5 LA 1 1 PD5 PD 1 1 D PETERSON,S.. 1 1 CHAN,T 1 1

'D INTERNAL: ACNW 2 2 ACRS 2 2 AEOD/DOA 1 1 AEOD/DSP/TPAB 1 1 AEOD/ROAB/DS P 2 2' NRR/DET/ECMB 9H 1 1 NRR/DET/EMEB9H3 1 NRR/DLPQ/LHFB11 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEABll NOTES'OPIESNRR/DREP/PRPB11 NRR/DST/SICB 7E NRR/DST/SRXB 8E 2

1 1

2 1

1 NRR/DST/SELB 8D N ~J)ST/SPLB8D1 G 02 1

1 1

1 1

1 1

1 RES/DSIR/EIB 1 1 GN LE 01 1 1 EXTERNAL EG&G BRYCE i J ~ H 3 3 L ST LOBBY WARD 1 1 LPDR 1 1 NRC PDR 1 1 NSIC MAYS,G 1 1 NSIC MURPHYiG A ~ 1 1 NUDOCS FULL TXT 1 1 1 .1 D

D NOTE TO ALL "RIDS" RECIPIENTS:

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

TOTAL NUMBER OF COPIES REQUIRED: LTTR 36 ENCL 36

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0 Arizona Public Service Company PALO VERDE NUCLEAR GENERATING STATION P,O. BOX 52034 ~ PHOENIX. ARIZONA 85072-2034 192-00674-JML/TRB/SBJ JAMES M. LEVINE VICE PRESIDEN~

t July ll, 1990 NUCLEAR PRODUCTION U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555

Dear Sirs:

Subj ect: 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 90-020-404 Attached please find Supplement Number 4 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 modification schedule.

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

Very truly yours Il ~/0 JML/TRB/SBJ/dmn Attachment cc: W. F. Conway (all with attachment)

J. B. Martin D. H. Coe T. L. Chan A. CD Gehr A. L. Gutterman

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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 4 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 '.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 accidhnt scenarios. The high range monitors must be declared inoperable when the low range monitors are inoperable.

Pursuant to Technical 'Specification 3.3.3.8 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 111? 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'PS 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.

I Special Report 2-SR-88-009-04 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 generat'ion 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.

This modification has been implemented by temporary modification on radiation detectors RU-141, RU-143 and RU-145 in Unit 1; radiation detectors'U-141, RU-143, and RU-145 in Unit 2; and radiation detectors RU-141 and RU-143 in Unit

3. The radiation detectors have not experienced any spiking since completion of the temporary modification. The temporary modification to RU-145 in Unit 3 could not be completed because of small to'lerances between the detector and its mounting collar. Information has been requested from the vendor to determine if the tolerance can be modified. Resolution should be obtained and the temporary modification should be completed by August 30, 1990; however, the tolerance cannot be modified to accommodate the temporary modification, if the temporary modification will be cancelled for RU-145 and the permanent change implemented in accordance with the schedule below.

A plant change request has been initiated to make the temporary modification a permanent design change. In the process of developing the permanent design change, enhancements to the design may be necessary. Only radiation monitors RU-141, RU-143, and RU-145 are being modified because beta scintillation detectors are significantly more sensitive than the detectors used in other radiation monitors. Development of the design change is expected to be completed by October 30, 1990. Necessary changes are expected to be implemented in Units 1, 2', and 3 within 90 days of materials receipt,

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