05000395/LER-2008-004

LER-2008-004, Technical Specification Violation due to Alternate AC Unavailability

Docket Number
Event date:	02-15-2007
Report date:	03-17-2009
Reporting criterion:	10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications
3952008004R01 - NRC Website

PLANT IDENTIFICATION

Westinghouse - Pressurized Water Reactor

EQUIPMENT IDENTIFICATION

XTF5052, Alternate AC Transformer

IDENTIFICATION OF EVENT

On three occasions during Cycle 17, Virgil C. Summer Nuclear Station (VCSNS) extended Emergency Diesel Generator outages beyond 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> for maintenance by taking credit for Alternate AC (AAC) as allowed by LCO 3.8.1.1 Action b.4. Surveillance testing during Refueling Outage 17 identified voltage regulation problems and an incorrectly installed reverse power relay which tripped the AAC supply breaker to the VCSNS vital buses. These test results called into question the availability of AAC, and a subsequent past operability determination led to the discovery, on August 11, 2008, that the AAC power source may not have been available during these periods.

EVENT DATES

2/15/2007, 3/01/2007, 3/27/2008 Condition Reports CR-08-02381 and CR-08-02477 were initiated to address this event.

REPORT DATE

10/09/08, Revision 0 03/17/09, Revision 1

CONDITIONS PRIOR TO EVENT

Mode 1, 100% Power

DESCRIPTION OF EVENT

On three separate occasions VCSNS entered LCO 3.8.1.1 Action b.4. for Emergency Diesel Generator (EDG) outages:

EDG1A: 02/12 - 02/18/2007 EDG1B: 02/26 - 03/01/2007 EDG1B: 03/24 - 03/30/2008 In accordance with Technical Specification LCO 3.8.1.1, the EDG must 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 />. However, the requirement for restoration of the EDG to operable status within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> may be extended to 14 days if the AAC power source is or will be available within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. Since past availability of the AAC could not be assumed, VCSNS violated Technical Specification LCO 3.8.1.1 anytime an EDG was inoperable greater than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Therefore, VCSNS violated Technical Specification LCO 3.8.1.1 on 2/15/2007, 3/01/2007, and 3/27/2008.

�

CAUSE OF EVENT

The AAC unavailabilty resulted from voltage regulation problems, an inadequately designed Reverse Power Relay (351S-7), and improperly installed wiring on the 387 bus differential relay.

ANALYSIS OF EVENT

The incorrectly installed reverse power relay called into question the past availabilty of the AAC. During the RF-17 testing the relay actuated and tripped the AAC supply breaker to VCSNS, when a load was being added to the AAC. Further investigation determined that the relay had been installed incorrectly. Even with the relay installed incorrectly, post modification testing and subsequent surveillance testing were successful.

Although the potential unavailability of the AAC resulted in a Technical Specification violation, a PRA evaluation determined that the safety significance was low (

CORRECTIVE ACTIONS

To address the voltage regulation issues, an enhanced prejob brief and procedural guidance have been put in place for controlling the Parr hydro units when adding VCSNS loads to the AAC.

The reverse power relay trip function has been interimly addressed by jumpering out this function. To prevent recurrence of AAC unavailabilty due to a reverse power trip, an engineering modification has been initiated to permanently remove the reverse power trip function.

The improperly installed bus differential relay wiring has been corrected.

PRIOR OCCURRENCES

There have been no other instances of Technical Specification violations related to AAC unavailability in the past three years.