05000341/LER-2012-001
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No, 05000 | |
| Event date: | 04-11-2012 |
|---|---|
| Report date: | 06-08-2012 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(v)(B), Loss of Safety Function - Remove Residual Heat |
| Initial Reporting | |
| ENS 47826 | 10 CFR 50.72(b)(3)(v)(B), Loss of Safety Function - Remove Residual Heat |
| 3412012001R00 - NRC Website | |
Initial Plant Conditions:
Mode 5 Reactor Power 0 percent
Description of the Event
On April 11, 2012, at approximately 1807 EDT, with the plant in Mode 5 during Refueling Outage 15 (RF15) and with Shutdown Cooling (SDC) in operation, the E1150F009, "Division 1 and 2 Shutdown Cooling Inboard Containment Isolation Valve," automatically closed. The 'A' Residual Heat Removal (RHR) [BO] pump tripped as a result of the valve closure. The valve closure resulted in an interruption of SDC, the primary means of decay heat removal for approximately 11 minutes. During this period, there was not a measurable increase in reactor temperature. The calculated time to boil was approximately 23.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
During the restoration of the Bus 65E Safety Tagging Record (STR), operators did not identify that a ground truck was still installed in position 65E-E4. When attempting to energize Division 2 Bus 65E from Division 1 through the 64T crosstie breaker and the 65E-E9 breaker per System Operating Procedure (SOP) 23.321, "Engineer Safety Features Auxiliary Electrical Distribution System," the breaker [BKR] immediately tripped open. A voltage transient occurred due to a fault on Bus 65E which resulted in a Group 4 (Shutdown Cooling/Head Spray) isolation (closure) of the E1150F009 shutdown cooling suction valve. The 'A' RHR pump tripped on loss of suction flow path as the shutdown cooling suction valve closed.
The Fuel Pool Cooling system was in service at the time of the event and was capable of removing decay heat.
The Reactor Cavity was flooded for refueling and the gates between the Reactor Cavity and the Fuel Pool were removed. Abnormal Operating Procedure 20.205.01, Loss of Shutdown Cooling, was entered, the Group 4 isolation was reset, and SDC was restored at 1818 EDT.
This event was reported to the NRC as an 8 hour9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> event under 10 CFR 50.72 (b)(3)(v)(B), event or condition that at the time of discovery could have prevented fulfillment of a safety function of structures or systems that are needed to remove residual heat, as documented in event notification 47826.
Significant Safety Consequences and Implications For the duration of this event, Fuel Pool Cooling and Cleanup (FPCCU) was in-service. The Reactor cavity was flooded and the gates between the Fuel Pool and the Reactor Cavity were removed for refueling. The RHR shutdown cooling was available for the duration of this event. There were no component failures associated with this event that would have prevented the valve from being reopened and the system from being restarted. All of the affected equipment responded as designed to isolate the containment and protect safety equipment.
Therefore, there were no safety consequences and no effect on public health and safety as a result of this event.
This event is being reported as an event or condition that at the time of discovery could have prevented fulfillment of a safety function of structures or systems needed to remove residual heat under 10 CFR 50.73 (a)(2)(v)(B).
Cause of the Event
The STR was not properly cleared before authorizing the performance of the SOP to energize Bus 65E from the maintenance tie breaker. Procedure 23.300, Breaker Operations, and Operations Department Expectation (ODE) 19, Safety and Configuration Tagging were not correctly implemented by operations personnel. A "Ground Truck Installed" sign that should have been placed on the breaker cubicle for 65E-E4 was not in place as required by 23.300 Section 6.5. The STR was also not completely cleared before authorizing the performance of the SOP to energize the bus from the 64T maintenance tie breaker. A review of the STR and the equipment walkdown prior to implementation of the STR did not identify that the ground truck remained installed. Strict compliance with procedures 23.300 and ODE-19 along with appropriate self checking would have ensured the standards were met, and could have prevented the problem.
Corrective Actions
The Group 4 isolation signal was reset, the SDC common suction valve was reopened, and SDC was established in 11 minutes.
The station implemented several equipment control tools to avoid a repeat event or reoccurrence. A checklist was developed for the preparer and reviewer of STRs. The requirements of actions to be performed by reviewers of STRs were reinforced by Operations Management during crew briefings and further reinforced during Just In Time Training. Requirements were established for licensed operators to conduct a walkdown (eyes on) of the bus prior to energization to insure bus is ready for current. Additional operator awareness tools were used to convey equipment status including the use of placards at the point of ground installation and in the Main Control Room.
Oil samples were taken April 12, 2012, on System Service Transformer (SST) 64 and House Transformer 1 and analyzed to ensure the transformers were not degraded by the temporary short to ground. Oil Sample results were the same as for the samples taken in March, 2012; therefore, there was no damage to the transformers.
Technical Evaluation TE-R14-12-037 was performed for a 3 phase to ground fault analysis to confirm that the postulated short circuit current was within the ratings of breakers 64T, 65E-E9, 65E-E12 and buses 65E (R1400S001E) and 64T cable bus (R1100S061) when Division 2 Bus 65E is fed by maintenance tie breaker 64T.
The ground fault current was determined to be within the equipment's momentary capabilities and the breaker's interrupting capabilities.
Additionally, a detailed walkdown of bus 65E breaker positions was performed, which did not identify any signs of damage as a result of the event.
Additional Information
A. Failed Component:
None identified.
B. Previous Licensee Event Reports (LERs) on Similar Problems:
No similar events were identified.