ML17305B019

Special Rept 1-SR-90-005:on 900725,performance of Loose Parts Detection Sys Might Result in Alarm Condition.Cause of Spurious Alarms Due to Sensitivity of Sys.Engineering Evaluation Determined Sys Operating Properly

ML17305B019
Person / Time
Site:	Palo Verde
Issue date:	08/21/1990
From:	James M. Levine ARIZONA PUBLIC SERVICE CO. (FORMERLY ARIZONA NUCLEAR
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
1-SR-90-005, 1-SR-90-5, 192-00686-JML-T, 192-686-JML-T, NUDOCS 9008300181
Download: ML17305B019 (8)

Text

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ACCESSXON NBR:9008300181 DOC.DATE: 90/08/21 NOTARIZED: NO DOCKET FACIL:STN-50-528 Palo Verde Nuclear Station, Unit 1, Arizona Publi 05000528 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:

Special Rept 1-SR-90-005:on 900725,performance of loose parts detection sys might result in alarm condition.

DISTRIBUTION CODE: IE22D COPIES RECEIVED:LTR ENCL L SIZE:

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

NOTES 'TANDARDIZED PLANT 05000528 /

RECXPIENT COPIES RECIPIENT COPIES A ID CODE/NAME LTTR ENCL XD CODE/NAME LTTR ENCL D

PD5 LA 1 1 PD5 PD 1 1 PETERSON,S. 1 1 TRAMMELL,C. 1 1 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 1 NRR/DLPQ/LHFB1 1 1 1 NRR/DLPQ/LPEB10 1 1 NRR/DOEA/OEAB11 1 1 NRR/DREP/PRPB11 2 2 NRR/DST/SELB 8D 1 1 EXTERNAL NRR/DST/SICB 7E NRR/DST/SRXB 8E RES/DSIR/EIB EG&G BRYCE i J H 1

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NOTE TO ALL "RIDS" RECIPIENTS:

PLEASE HELP US TO REDUCE iVASTE! CONTACT. THE DOCUb!ENT CONTROL DESK, ROOil PI-37 (EXT. 2N79) TO ELIilINATEYOUR NAiiIE FROiil DISTRII)UTION LISTS FOR DOCUiIENTS YOU DON'T NEED!

TOTAL NUMBER OF COPIES REQUIRED: LTTR 36 ENCL 36

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Arizona Public Service Company PALO VERDE NUCLEAR GENERATING STATION P.O, BOX 52034 ~ PHOENIX, ARIZONA 85072-2034 JAMES M, LEVINE 192-00686-JML/TRB/SBJ VICE PAESIDEN7 August 21, 1990 NDCt.EAR PRDDUC7ION U. S. Nuclear Regulatory Commission NRC Document Control Desk Pl-37 Washington, D.C. ,20555

Dear Sirs:

Subj ect: Palo Verde Nuclear Generating Station (PVNGS)

Unit 1 Docket No. STN 50-528 (License. No. NPF-41)

Special Report 1-SR-90-005 File: 90-020-404 Attached please find Special Report 1-SR-90-005 which is being voluntarily submitted to describe the performance of the Unit 1 Loose Parts Detection System.

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

Very truly yours, JML/TRB/SBJ/dmn Attachment cc: W. F. Conway (all w/attachment)

J. B. Martin C. M. Tramell D. H. Coe A. C. Gehr A. H. Gutterman INPO Records Center

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PALO VERDE NUCLEAR GENERATING STATION UNIT 1 License No. NPF-41 Docket No. 50-528 Special Report 1-SR-90-005 Initial Conditions:

On July 25, 1990 Palo Verde Unit 1 was in Mode 1 (POWER OPERATION) at one hundred percent power with the Reactor Coolant System (RCS) at normal operating temperature and pressure.

Descri tion of Event:

This Special Report is being voluntarily submitted to provide information on the performance of the Unit 1 Loose Part Detection System (LPDS).

The Palo Verde Unit 1 Loose Parts Detection System, (LPDS) consists of eight (8) channels. Each channel consists of a piezoelectric crystal motion sensor and associated amplification, indication, and recording circuitry. The sensors are positioned in the following locations: two (2) mounted on the Reactor Vessel upper head (channels 1 and 2), two (2) mounted on the Reactor Vessel lower incore nozzle (channels 3 and 4),

and one (1) on each of the two (2) Steam Generators'nlet and outlet nozzles (channels 5, 6, 7 and 8). The piezoelectric sensors detect the loose parts using acoustic signals which are generated when loose parts impact a Reactor Coolant System component or structure. Signals in excess of the alarm setpoint will result in an alarm condition. The alarms are the "latch-on" type, i.e., the alarms will remain on'when the system returns to normal and will not clear until the alarm is manually reset. There is one alarm indicator in the Control Room for the eight channels such that a "latch on" alarm effectively renders the Control Room alarm indication inoperable for the remaining channels upon receipt of an alarm condition. In addition to the alarm in the Control Room, tape recorders will start when the system is in 'Auto'. There are two tape recorders; each tape recorder can record four system channels at a time.

Technical Specification 3.3.3.7 requires all eight channels of LPDS to be OPERABLE in Modes 1 and 2 (POWER OPERATIONS and STARTUP). Tech'nical Specification 4.3.3.7 requires each channel to be demonstrated OPERABLE by a) a channel check at least once per 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, b) a Channel Functional Test at least once per 31 days, and c) a Channel Calibration at least once per 18 months'

NRC Document Control Desk Special Report 1-SR-90-005 Page 2 During the previous fuel cycle (March 1988 to March 1989) channel 5, located on Hot Leg 1A, experienced numerous spurious alarms. An engineering evaluation completed in October 1988 determined the system was functioning properly. The channel 5 alarm setpoint was temporarily raised and additional manual monitoring of the LPDS was initiated during the remainder of the fuel cycle (Reference 'Special Report 1-SR-88-008).

During the subsequent refueling outage, the channel 5 alarm setpoint was re'set, the required surveillance tests were performed, and the system placed in service The LPDS was not declared operable because of documentation that could not be closed until after full power was achieved. With the reactor at full power, the LPDS was monitored and Channel 5 was found to be spuriously activating. Therefore, the LPDS was not declared operable pending an evaluation of the actuations. The surveillance tests required by the Technical Specification 4.3.3.7 were performed and kept current during the time the evaluation was being performed. On June 25, 1990 at approximately 1951 MST Unit 1 entered Mode 2 (STARTUP). Technical Specifications permit entry into Mode 1 or Mode 2 with the LPDS inoperable. Unit 1 subsequently entered Mode 1 on June 30, 1990 at approximately 0226 MST.

An engineering evaluation determined that LPDS was operating properly.

The spurious alarms were caused by the system sensitivity required to meet the requirements of Regulatory Guide 1.133, the same cause established in 1988.

Following the engineering evaluation, an action plan for responding to and monitoring the LPDS after spurious alarms was developed. On July 25, 1990 at approximately 1910 MST, LPDS was declared operable.

Cause of Event'he cause of the LPDS Spurious alarms is the sensitivity of the system, as discussed above. The LPDS Channel response is reflective of the excitative energy from the Reactor Coolant System (RCS). APS has observed that, at different power levels and during different plant transients, RCS excitative energies vary which affect the response of the LPDS. Also, other sources (e.g., flow vortexing, core barrel bypass flow, etc.) can produce energy waves which excite the accelerometers.

In many cases, it takes a significant length of time after a plant transient for the RCS to "stabilize" to the point where spurious LPVMS alarms do not occur. This sensitivity is required to meet the requirements of Regulatory Guide 1.133.

Corrective Actions:

An engineer'ing evaluation was performed and determined LPDS was operating properly. The LPDS was declared operable on July 25, 1990 prior to the 30 day Technical Specification Action expiring.

NRC Document Control Desk Special Report 1-SR-90-005 Page 3 The operating procedure for the LPDS has been revised to include a 'high alarm rate condition'lassification for LPDS channels that alarm four or more times in one shift without any 'correlation to plant events or conditions. If a channel is determined to be in the 'high alarm rate condition', the audio from the channel will be monitored once per shift instead of on each alarm occurrence, and a work authorization document initiated to have the channel evaluated every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. The 'high alarm rate condition's cancelled if a channel does not alarm for 24 .hours.

APS is continuing to evaluate the LPDS to identify opportunities for improvements. An Event Analysis Computer modification is under development which is intended to enhance the ability of the system to discriminate false alarms.