05000530/LER-1998-002

LER-1998-002,

Event date:	9-9-0106
Report date:	5-0-0053
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
5301998002R01 - NRC Website

PDR ADOCK

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LICENSEE EVENT REPORT (LER) TEXT CONTINUATION == DOCKET NUMBER LER NUMBER PAGE ==

FACILITY NAME

015101010151310 == REPORTING REQUIREMENT: ==

This LER (50-530/98-002-01) is being submitted pursuant to 10 CFR 50.73(a)(2)(i)(B), an operation or condition prohibited by the plant's Technical Specification.

Specifically, the power supply receptacle (RCP) for the "B" train Hydrogen Recombiner (HP)(BB) was cross-wired resulting in equipment inoperability in excess of the Technical Specification action completion time.

Also, prior to implementation of Improved Technical Specification (ITS) on August 13, 1998, there was no Limiting Condition For Operation (LCO) by which Unit 3 could operate without at least one Hydrogen Recombiner operable. Therefore, during the periods of time prior to implementation of ITS, that the "B" train receptacle was cross-wired, and the redundant "A" train Hydrogen Recombiner was inoperable, or those times when the Hydrogen Purge system (HP)(BB) system was inoperable, the plant was in Technical Specification 3.0.3. Note: Improved Technical Specification 3.6.7 Condition B allows for both Hydrogen Recombiners to be inoperable up to seven days provided the Hydrogen Purge system is available.

2. EVENT DESCRIPTION:

On August 14, 1998, at approximately 1600 MST, Palo Verde Unit 3 was in Mode 1 (POWER OPERATION), operating at approximately 100 percent power when testing revealed that the 480 volt, three phase, alternating current power supply receptacle for the "B" train Hydrogen Recombiner was cross-wired wired (e.g., incorrectly phased). The power supply receptacle was configured such that had it been utilized, the blower motor (MO) of the supplied Hydrogen Recombiner would have rotated in the reverse direction.

Improved Technical Specification, Limiting Condition for Operation 3.6.7 was entered until the wiring configuration was corrected and demonstrated operable at approximately 1740 MST, on August 14, 1998.

Investigation results indicate that the Unit 3 "B" train Hydrogen Recombiner power receptacle was cross-wired when initially terminated during construction, in October, 1986. All other Hydrogen Recombiner power supply receptacles were tested and verified to be wired correctly.

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ASSESSMENT OF THE SAFETY CONSEQUENCES AND IMPLICATIONS OF THIS EVENT:

The hydrogen recombiners provide for controlling the bulk hydrogen concentration in containment (NH) to less than the lower flammable concentration of 4.0 percent by volume following a Loss-of-Coolant design basis accident (DBA). The control of hydrogen concentration: 1) prevents a containment-wide hydrogen burn, thus ensuring the pressure assumed in the analysis is not exceeded and minimizing damage to safety related equipment located in containment, 2) ensures containment pressure would not exceed the design basis pressure used in the structural design of containment, and 3) ensures the maximum leakage from containment during a hypothetical event would remain within 10 CFR 50 Appendix J requirements.

During the period of time the "B" train Hydrogen Recombiner was inoperable due to the cross-wired power supply receptacle, the "A" train Hydrogen Recombiner and backup system (i.e. the Hydrogen Purge system) were available to control containment hydrogen levels within design limits had they been needed. Unavailability of either the "A" train Hydrogen Recombiner or the backup Hydrogen Purge system was limited to brief periods during the performance of surveillance testing or periodic maintenance. During the period of time the "B" train Hydrogen Recombiner was inoperable, there was at least one system available at all times to control Hydrogen in the containment.

Additionally, had the cross-wired power supply receptacle been utilized, the blower motor of the supplied Hydrogen Recombiner would have rotated in the reverse direction. Upon sensing that minimum flow was not being met, protection devices would have shut down the recombiner prior to any motor damage and would initiate a trouble alarm in the control room. Readily observable conditions and reasonable operator actions would assure prompt equipment recovery had the "B" train recombiner been needed.

There were no adverse safety consequences as a result of this event. The event did not result in any challenges to the fission product barriers or releases of radioactive materials. This event did not adversely affect the safe operation of the plant or the health and safety of the public.

4. CAUSE OF THE EVENT:

Conclusive evidence was not produced to indicate why the power receptacle for the "B" train Hydrogen Recombiner was not terminated (wired) in accordance with plant configuration drawings. However, evidence was uncovered that suggests the initial error was made during the construction phase of Unit 3. Specifically, Brady brand wire markers were found applied over the factory embossed wire numbers, and a review of work

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records indicate there has been no subsequent work on this device since the initial termination of the power receptacle. Therefore, APS has concluded that the error occurred during the construction phase of the plant, and was attributed to personnel error, since plant configuration drawings were not followed. Since the other Hydrogen Recombiner power receptacles were wired correctly, this appears to be an isolated case of personnel error.

The lack of verification/functional testing upon completion of the power receptacle termination was a contributing factor, because the phase rotation problem would have been revealed had the testing been performed.

Although current procedures require Alternating Current (AC) motors be tested for correct phasing (rotation), when the Hydrogen Recombiners were initially installed in Unit 1, Unit 3 was still under construction. A review of startup documentation revealed that phase rotation was not verified for the three phase 480 VAC motors in Units 2 and 3.

5. STRUCTURES, SYSTEMS, OR COMPONENTS INFORMATION:

The Containment Hydrogen Control System (HP)(BB) consists of containment hydrogen recombiners, gas analyzers, and post-accident hydrogen purge exhaust system. It provides equipment necessary to prevent the hydrogen concentration in the containment from exceeding 4 percent by volume following a loss-of-coolant accident (LOCA).

Palo Verde has two separate, redundant hydrogen recombiners (Train "A" and "B"), both of which are installed in Unit 1. The two 100% capacity independent external hydrogen recombiners are shared among the three units and can be moved between units if necessary. Each consists of controls, a power supply (JX), and a recombiner located in the Auxiliary Building (NF). Recombination is accomplished by heating a hydrogen air mixture above 1150°F. The resulting water vapor and discharge gases are cooled prior to discharge from the recombiner. Air flows through the unit at 50 cubic feet per minute with a 5 hp centrifugal blower (BLO) in the unit providing the motive force.

A single recombiner is capable of maintaining the hydrogen concentration in containment below the 4.0 percent flammability limit. Two recombiners are provided to meet the requirement for redundancy and independence.

Each recombiner is powered from a separate Engineered Safety Features bus.

The post-accident hydrogen purge exhaust air filtration unit (AFU)(FLT) serves as a backup to the hydrogen recombiner and can be used to control Hydrogen concentration in the containment. It is a portable unit which LICENSEE EVENT REPORT (LER) TEXT CONTINUATION AC !LITT NAME DOCKET NUMBER LER NUMBER == PAGE ==

can be connected to any of the three plant units as needed. It filters the potentially radioactive particulate matter and iodine from the air.

6. CORRECTIVE ACTIONS TO PREVENT RECURRENCE:

The cross-wired power supply receptacle for the "B" train Hydrogen Recombiner was re-configured and verified to be correct at approximately 1740 MST, on August 14, 1998. All other Hydrogen Recombiner power supply receptacles were tested and verified to be_configured correctly by 1600 MST, August 14, 1998.

When the cross-wired power receptacle condition was initially identified, it was potentially transportable to the Unit 1, 2, and 3 Hydrogen Recombiners. However, phase testing using a motor test rig demonstrated the problem was limited to the Unit 3 "B" train hydrogen recombiner power receptacle. Evaluation of the condition revealed that the Hydrogen Recombiners were the only safety related equipment that can be transported from unit to unit and that was susceptible to the cross-wired condition.

Other equipment (i.e., Hydrogen Purge Unit and the non-class 1E temporary electrical powered breathing air compressor (BH)(CMP)) that can be transported from unit to unit was not susceptible to the cross-wired condition.

Current procedures (i.e., 32MT-9ZZ84, "AC Motor Operational Testing") ensure motor installations are correctly configured by requiring that phase rotation be verified prior to placing a motor in service.

7. PREVIOUS SIMILAR EVENTS:

No other previous events have been reported pursuant to 10 CFR 50.73 in the last three years.

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CATEGORY 1 REGULATORY INFORMATION DISTRIBUTION SYSTEM (RIDS) ACCESSION NBR:9901060295 DOC.DATE: 98/12/31 NOTARIZED: NO DOCKET # FACIL:STN-50-530 Palo Verde Nuclear Station, Unit 3, Arizona Publi 05000530 AUTH.NAME == AUTHOR AFFILIATION ==

OVERBECK,G.R. Arizona Public Service Co. (formerly Arizona Nuclear Power RECIP.NAME == RECIPIENT AFFILIATION ==

Records Management Branch (Document Control Desk) SUBJECT: Forwards LER 98-002-01,prepared & submitted pursuant to 10CFR50.73.LER describes discovery & correction of cross- wired power supply receptacle for "B" train hydrogen recombiner.

NOTES:Standardized plant.

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