On January 27, 2005, Crystal River - Unit 3 (CR-3) discovered an installation subject to a single failure that could prevent both
Emergency Diesel Generators (EDGS) and both offsite power sources from supplying power to their respective Engineered Safeguards (
ES) Busses. This is a condition contrary to
10CFR50.72 (b)(3)(ii)(B).
The installation involves the 4.16 Kv supply breakers from the offsite power transformer (OPT) and the Back-up Engineered Safeguards Transformer (BEST) which are the two required offsite power sources. From the OPT, one breaker supplies the 'A' ES Bus and a second breaker supplies the 'B' ES Bus. From the BEST, one breaker supplies the 'A' ES Bus and a second breaker supplies the 'B' ES Bus. A traditional (non-nuclear) design for such pairs of supply breakers includes current transformers that are connected to each other for each phase and a watt hour meter from those connections to monitor power. These circuits were installed around 1990 to support the coordination of the new 230 Kv breakers to supply the OPT and the coordination with the 230 Kv supply breakers for the new BEST.
Should a failure of the wire connecting the current transformers or the watthour meter occur such that the ES Bus supply breakers' lockout relays are actuated, all breakers supplying and receiving power via the ES Busses would be opened and locked out. The result is that neither EDG nor the offsite power source would be able to automatically supply power to its respective ES Bus.
CR-3 is currently disconnecting and isolating the watthour meters and removing the connection between the respective breakers' current transformers.
Licensee entered Tech Spec 3.8.9.1 at 1830 hours0.0212 days <br />0.508 hours <br />0.00303 weeks <br />6.96315e-4 months <br /> based on single failure but considers both ES busses operable.
The NRC Resident Inspector was notified of this event by the licensee.
- Update on 01/28/05 at 1655 EST from Guy McCallum to MacKinnon ****
On January 28, 2005, Crystal River - Unit 3 (CR-3) corrected the single failure vulnerability associated with the Engineered Safeguards (ES) Busses.
A permanent modification which removed the single failure vulnerability for the offsite power transformer (OPT) was completed at (0152), and the modification for the Back-up Engineered Safeguards Transformer (BEST) was completed at (0644). R2DO (T. Decker) notified.
The NRC Resident Inspector was notified of this event by the licensee.
