05000443/LER-2007-002
| Seabrook Station | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4432007002R00 - NRC Website | |
I. Description of Event
On April 5, 2007 with the unit in Mode 1 at 100% power, Seabrook Station declared the turbine-driven emergency feedwater pump (TDEFWP) [BA, P] inoperable because the turbine steam supply valve (MS-V395) [SB, V] stroke time was outside its acceptable limit. The noncompliance was discovered during an NRC Component Design Basis Inspection. The design basis stroke time for MS-V395 is five to 15 seconds; however, a review of past surveillance tests revealed that the actual stroke time was less than five seconds. This condition, which rendered the TDEFWP inoperable, existed on three occasions because the surveillance test for measuring the valve's stroke time incorrectly specified a minimum stroke time of four seconds rather than five seconds. While the technical specifications (TS) require a plant shutdown if an emergency feedwater pump is 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 plant continued to operate in Mode 1 for more than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> with the TDEFWP inoperable.
Consequently, this event resulted in a condition prohibited by the technical specifications.
II. Cause of Event
The cause of the event was a human error, which resulted in a failure to identify that a design change inserted an incorrect minimum stroke time for MS-V395 in station documents. Design change DCR 87-12, implemented in 1989, changed the maximum opening time for MS-V395 from ten to 15 seconds; the five second minimum opening time was unaffected by this change. However, the drawings that were marked up to incorporate this change inappropriately changed the minimum stroke time for MS-V395 from five to four seconds. Subsequent reviews of these revised documents failed to detect this error. As a result, the incorrect stroke time for MS-V395 was translated from the drawings into the surveillance procedure that measures the valve's stroke time.
III. Analysis of Event
The steam supply for the TDEFWP is from either of two main steam headers via branch lines connected upstream of the main steam isolation valves. The branch lines contain normally closed, fail-open air-operated isolation valves, MS-V393 and MS-V394 [SB, V]. These branch lines join a common steam supply line that contains MS- V395, a normally closed, fail-open air-operated valve. MS-V393 and MS-V394 open in response to an emergency feedwater (EFW) actuation signal to admit steam to MS-V395, which is timed to open sequentially following opening of either MS-V393 or MS-V394. The sequential opening of MS-V395 allows for pressurizing the EFW steam header to discharge accumulated condensate prior to introducing steam to the turbine governor valve.
Operability of the TDEFWP is contingent on the ability of the steam supply valves to perform their specified function as designed. Consequently, following discovery that MS-V395 did not meet its minimum required stroke time, the TDEFWP was declared inoperable at 1930 on April 5, 2007. The TDEFWP returned to operable status at 0518 on April 6, 2007 when the stroke time for MS-V395 was restored to an acceptable value. A review of test data showed that the stroke time for MS-V395 was less than the allowable minimum value between April 30 and October 5, 2005; between December 28, 2005 and March 22, 2006; and from June 14, 2006 to April 6, 2007.
Because the plant operated in Mode 1 for more than the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowed outage time permitted by the TS for an inoperable EFW pump, this event was a condition prohibited by the TS.
Although this event rendered the TDEFWP inoperable due to the failure to meet the stroke time, no adverse consequences resulted from this occurrence and the EFW system remained functional and fully capable of performing its specified function. MS-V395 is a dual train valve that actuates on train A and train B initiation signals. The stroke time for a train A actuation remained within acceptable limits and only the train B stroke time was affected by this event. Further, the shortest observed train B stroke time of 4.49 seconds did not adversely impact performance of the TDEFWP. During past testing, the TDEFWP started and operated satisfactorily with MS-V395 opening in less than five seconds. In addition, the incorrect stroke time did not impact the time delay for the sequential opening of MS-V395 following opening of either MS-V393 or MS-V394. Therefore, the condition did not involve a safety system functional failure.
This event is of regulatory significance because it met the reporting criterion of 10 CFR 50.73(a)(2)(i)(B) for a condition prohibited by the TS. The event had no adverse impact on the plant or on the health and safety of the public or plant personnel. No plant transients, systems actuations, or consequences resulted from the event. No other inoperable structures, systems, or components contributed to this event.
IV.Corrective Action The stroke time for MS-V395 was adjusted and restored to an acceptable value.
This event will be reviewed with engineering personnel to reinforce the use of human error prevention techniques.
V. Similar Events Seabrook Station has experienced no similar events in the past three years.