05000341/LER-2012-002
| Docket Number Sequential Revmonth Day Year Year Month Day Yearnumber No. 05000 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv)(A), System Actuation |
| Initial Reporting | |
| ENS 47868 | 10 CFR 50.72(b)(3)(iv)(A), System Actuation |
| 3412012002R00 - NRC Website | |
Initial Plant Conditions:
Modee 4 Reactor Powere 0 percent
Description of the Event
On April 26, 2012, at 10:12 am EDT, during Refueling Outage 15 (RF15) with the Reactor Pressure Vessel (RPV) Hydrostatic Pressure Test, in progress, a high pressure reactor scram occurred. The test was being conducted in accordance with Infrequently Performed Test and Evolution (IPTE) 12-03, RPV Hydrostatic Test.
Operators were monitoring RPV pressure using an Integrated Plant Computer System (IPCS) [CPU] average pressure point. However, one input of the average pressure point was valved out for scheduled excess flow check valve (EFCV) testing. This resulted in a lowering of indicated pressure while actual pressure was rising. When actual pressure reached the scram setpoint, a valid scram occurred. The Reactor Protection System (RPS) RPV high pressure signals for trip system A, channel 1 and trip system B, channel 1 came in on a RPV high pressure.
All control rods were already fully inserted in the reactor core at the time of the scram. The RPS and other plant equipment responded as expected to the RPV high pressure condition.
The IPCS pressure indication selected by the Licensed Control Room Staff became inaccurate because of the EFCV testing. The inaccuracy was not recognized prior to RPV pressure reaching the high pressure setpoint.
RPV pressure lowered to 600 psig as expected following the scram. The plant was stable and the scram was reset at 10:13 am.
Significant Safety Consequences and Implications The plant was in Mode 4 "Cold Shutdown," at the time of the Reactor Scram. All Control Rods were already fully inserted in the Reactor Core. The RPS and other plant equipment responded as expected to the RPV high pressure condition.
RPV Steam Dome Pressure Transmitters [PIT] B21N078A and B21N078B remained in service during the pressure transient. Both transmitters detected the increase in RPV pressure accurately. When the pressure reached the trip setpoint of 1093 psig, a valid scram signal was initiated. Transmitter B21N078A provides input to the RPS trip system A and transmitter B21N078B provides input to the RPS trip system B. With a half scram signal in both RPS A and B trip systems, a full scram occurred as expected.
The plant responded as expected to the RPV high pressure condition and no safety limits were exceeded.
Therefore, there were no safety consequences and no effect on public health and safety as a result of this event.
This event was reported as an 8-hour non-emergency notification for a valid RPS system actuation per 1 OCFR5 0.72(b)(3)(iv)(A) as documented in event notification number 47868. This report is provided in accordance with 10 CFR 50.73(a)(2)(iv)(A), "Any event or condition that resulted in manual or automatic actuation of any of the systems listed in paragraph (a)(2)(iv)(B).
Cause of the Event
When the EFCV testing was released, the control room operators failed to recognize that one of the IPCS points being monitored would become invalid as part of the EFCV test. Inadequate impact evaluation for EFCV testing led to a failure to properly monitor a critical parameter. The IPCS point being monitored indicated a lowering pressure while actual RPV pressure was rising. The Control Room staff allowed the pressure to increase based on an IPCS computer point that averaged RPV pressure inputs where one of the inputs did not reflect the actual RPV pressure. The Licensed Operator did not use the indications specified in the RPV system leakage test procedure to validate reactor pressure.
Corrective Actions
This event was entered into the Fermi 2 Corrective Actions Program. The scram was reset and prior to resumption of the RPV hydrostatic pressure test (1) All instruments affected by EFCV testing were identified on the main control room panels, (2) A dedicated operator monitored reactor pressure on a wide range pressure recorder unaffected by EFCV testing and communicate pressure changes with shift personnel, and (3) IPCS screens were updated to display redundant RPV Pressure instruments not affected by EFCV testing.
Long term corrective actions include revisions to procedural requirements and inclusion of the event in operator requalification training as part of refuel outage preparation.
Additional Information
A. Failed Component:
None identified.
B. Previous Licensee Event Reports (LERs) on Similar Problems:
No similar events were identified.