05000338/LER-2005-001
| North Anna Power Station | |
| Event date: | 10-03-2005 |
|---|---|
| Report date: | 11-29-2005 |
| 3382005001R00 - NRC Website | |
FACILITY NAME (1) DOCKET LER NUMBER 6) PAGE (3) 1.0 DESCRIPTION OF THE EVENT The Low Temperature Overpressure Protection (LTOP) System controls Reactor Coolant System (RCS) (EIIS System-AB) pressure at low temperature so integrity of the reactor coolant pressure boundary is not compromised by violating the LTOP System design basis pressure and temperature limit curve. LTOP prevention is most critical during shutdown when the RCS is water solid and a mass or heat input transient can cause a very rapid increase in RCS pressure when little time is available for operator action to mitigate the event. Technical Specification (TS) applicability includes Mode 4 when any RCS cold leg temperature is less than or equal to 280 degrees Fahrenheit, Mode 5, and Mode 6 when the reactor vessel head is on.
The potential for a low temperature overpressure event is minimized by limiting the mass input capability. To limit the coolant input capability a maximum of one low head safety injection (LHSI) pump and a maximum of one charging pump are verified capable of injecting into the RCS.
On October 3, 2005, with Unit 2 in Mode 5 for a scheduled refueling outage it was determined that all required actions for Low Temperature Overpressure Protection (LTOP) System controls were not implemented. A second independent means to prevent more than one low head safety injection (LHSI) pump (EIIS System-BP, Component-P) and charging pump (EIIS System-BQ, Component-P) from being capable of injecting into the Reactor Coolant System (RCS) was not being performed. The Technical Specifications (TS) Bases states two independent means are required to prevent a pump start such that a single failure or single action will not result in an injection to the RCS.
The procedures controlling the LHSI and charging pumps operations only required the pumps to be placed in pull to lock. They did not require the breakers (EIIS Systems-BP and BQ, Component-BKR) to be racked out under administrative control. The procedures also did not include an alternate method of control using at least two independent means to prevent an inadvertent injection into the RCS. This condition had existed since implementation of the Improved Technical Specifications (ITS) in August 2002.
2.0 SIGNIFICANT SAFETY CONSEQUENCES AND IMPLICATIONS This event posed no significant safety implications since the LTOP System design basis pressure and temperature limit curve were never violated. Therefore, the health and safety of the public were not affected by this event. This event is reportable pursuant to 10 CFR 50.73 (a)(2)(i)(A) for a condition prohibited by TS.
FACILITY NAME (1)� DOCKET LER NUMBER 6) PAGE (3) 3.0 CAUSE During the process of converting the original TS to the ITS, the requirement to implement two independent means to prevent an inadvertent injection into the RCS was not identified and therefore changes to the affected procedures that implement the Technical Specification requirements of LCO 3.4.12 were not completed.
4.0 IMMEDIATE CORRECTIVE ACTION(S) With Unit 2 in Mode 5 for a refueling outage, Operations personnel entered the action for TS 3.4.12. The Unit 2 discharge motor operated valves (EIIS Systems-BP and BQ, Component-ISV) for the LHSI and charging pumps were verified closed.
5.0 ADDITIONAL CORRECTIVE ACTIONS Operating and Emergency procedures for both units were revised to require a second independent action to prevent injection into the RCS. Maintenance Operating Procedures will be revised prior to their next required use.
6.0 ACTIONS TO PREVENT RECURRENCE The station has been using the ITS for over three years and this is the first incident where a condition identified in the TS Bases was not adequately addressed by the implementing procedures resulting in a condition prohibited by TS. The event is considered an isolated case. Revisions to the procedures controlling the LHSI and charging pumps operations will ensure the actions required by TS 3.4.12 are satisfied.
7.0 SIMILAR EVENTS None 8.0 ADDITIONAL INFORMATION None