05000335/LER-2003-005

LER-2003-005,

Event date:	12-03-2003
Report date:	02-02-2004
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications 10 CFR 50.73(a)(2)(v), Loss of Safety Function
3352003005R00 - NRC Website

FACILITY NAME (1)

DOCKET

HUMBER [2) LER NUMBER (6)

Description of the Event

On December 3, 2003, St. Lucie Unit 1 was in Mode 1 at 100 percent reactor power.

During performance of the containment fan cooler monthly surveillance (procedure 1-OSP-25.02), the containment vacuum relief valve (EIIS:BF:FCV) FCV-25-8 failed to stroke full open on demand. When pressure returned to the reset point, the valve closed. Operations entered Technical Specification (TS) Action Statement (AS) 3.6.5.1. that requires with one vacuum relief line inoperable, the vacuum relief line be restored to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> or the unit must be in at least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br /> and in COLD SHUTDOWN within the following 30 hours3.472222e-4 days <br />0.00833 hours <br />4.960317e-5 weeks <br />1.1415e-5 months <br />.

During the repair activities the valve actuator quick exhaust valve (EIIS:BF:V] (QEV) was found to be defective and replaced. Subsequent valve strokes went full open and the valve post maintenance stroke time test was satisfactorily completed.

The opposite train valve, FCV-25-7, had failed inservice testing (IST) stroke time testing two days earlier and was repaired on December 2, 2003. The earlier failure was also due to a defective QEV, which was replaced. When both of the QEVs were later disassembled, the internal urethane diaphragms were found to be failed.

Protection of the containment vessel against excessive external pressure is provided by two independent vacuum relief lines each sized to prevent the differential pressure between the containment and the shield building atmosphere from exceeding the design value of 0.70 psig. Each vacuum relief assembly consists of a check valve inside and an automatic air-operated butterfly valve outside the containment vessel.

Actuation of the butterfly valve is controlled by differential pressure between the shield building annulus and the containment vessel. Redundant transmitters sense the differential pressure and provide a signal to the pilot solenoid on the air-operated butterfly valve to open.

The vacuum breaker check valve is required to open at 1.1" wg differential pressure and the butterfly valve is set to open at a differential pressure of 2_25' wg.

Since the vacuum relief valves also perform a containment isolation function in case of a LOCA, the automatic butterfly valves are designed to fail closed. The electrical supply for the controls of each of the redundant automatic valves is from a separate emergency 125 V dc bus. The design is such that no active single failure can prevent operation of both redundant vacuum relief assemblies.

Cause of the Event

The cause of the QEV failure is the time-dependent degradation of its urethane diaphragm. During the maintenance troubleshooting for both valves, FPL determined that each QEV diaphragm had failed, allowing air to bypass the actuator as air exhausted through the QEV quick discharge port. For FCV-25-8, this resulted in failing to provide enough air to the valve operator to completely open the valve.

For FCV-25-7, this resulted in failing the valve closed.

Maintenance history indicates that the OEVE had been replaced in October 1999 for FCV-25-7 and -8. The QEV diaphragms failed due to the same cause within two days of each other. A review of the preventive maintenance (PM) database showed that the actuators of both valves had been overhauled in 1999 using the Bettis actuator overhaul procedure. While'the procedure did not specifically mention the replacement of the QEVs the "materials used" section of the work orders showed that the QEVs were replaced. There was no material change from that of the QEV diaphragms replaced in 1999. Industry operating experience was sear � and the diaphragm material is 11t � 11111141.11 FACILITY NAME (1)

DOCKET

LER NUMBER (6) suited for the application. However, based on the QEV diaphragm age-related degradation, a preventive maintenance (PM) change was processed to initiate a QEV overhaul with a 36-month frequency. Generically, St. Lucie will assess the current site-wide PM process as part of an upcoming PM optimization program.

Analysis of the Event

Based on the observed test failures and the common cause age-related failure mechanism of the QEV diaphragms, a failure to open on demand would have been highly likely during a containment vacuum relief event. The time related common cause failure mechanism is indicative of a condition where both trains of containment vacuum breakers were unable to perform their specified function in excess of the allowed Technical Specification outage time. Therefore, this condition is reportable under 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by Technical Specifications.

Although this condition resulted in a loss of the containment vacuum function (an analyzed transient), this did not result in the loss of a safety function required to shutdown the reactor, remove decay heat, control releases, or mitigate the consequences of an accident. Therefore, 10 CFR 50.73(a)(2)(v) reporting criteria are not applicable.

Analysis of Safety Significance The containment vacuum breakers have a safety-related containment integrity function.

The failed QEV diaphragms had no impact on the containment vacuum breakers ability to remain closed and provide a passive containment pressure integrity function. The vacuum relief function is provided as a protective feature for the containment liner.

Protection of a fission product barrier against transients warrants that the vacuum relief function be governed by a Technical Specification.

The St. Lucie Unit 1 Updated Final Safety Analysis Report (UFSAR) analysis for vacuum relief assumes the operation of one vacuum relief line fully open, while the redundant line is assumed to be inoperable. The transient includes activation of all containment fan coolers concurrent with operation of both trains of the containment spray system. The vacuum relief line fully opens within a few seconds to prevent the differential pressure between the containment and the shield building atmosphere from exceeding the design basis limit of 0.70 psig. The maximum differential pressure from the analysis is 0.66 psig. Failure of the vacuum relief function could challenge the containment liner; however, the inadvertent containment-cooling transient is not a core damage or fission product release design basis accident.

Likewise, during design bases accidents that require containment integrity to contain fission products, the containment structure is not subjected to vacuum conditions.

Therefore, this condition bad no adverse effect on the health and safety of the public.

This condition is not applicable to St. Lucie Unit 2 as the containment vacuum relief line valve actuators do not use the St. Lucie Unit 1 QEV design. These QEVS are not used in any other applications for St. Lucie Units 1 and 2.

Corrective Actions

1. The actuators for FCV-25-7 and -8 were repaired and returned to service.

2. A preventive maintenance change request was submitted to overhaul the actuator OEVs for FCV 25-7 and -8 on a 36-month basis.

lZli NW 36U Moto NU 1.111 386111-26111 LER NUMBER (6)

Failed Components

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