05000397/LER-2004-005
| Columbia Generating Station | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(iv), System Actuation |
| 3972004005R00 - NRC Website | |
Event Description
During a reactor startup on August 15, 2004, with reactor power at approximately 18%, plant operators manually initiated the Reactor Protection System (RPS) in response to decreasing water level in the Reactor Pressure Vessel (RPV) following a reactor feedwater pump (RFW-P-1A) trip. The steam driven RFW-P-1A tripped as designed due to high level in the pumped drain tank (MD-TK-1).
The Reactor Core Isolation Cooling [BN] system was used to maintain RPV level until pressure was reduced to within the capacity of the condensate booster pumps.
Immediate Corrective Action Associated normal operating and annunciator response procedures were updated to verify normal hotwell level conditions and refrain from continued operation in an alarm state during relevant plant conditions. Operating crews were briefed on the changes.
A walkdown was conducted to identify other controllers, which were set to operate at high or low ends of the control band. During this walkdown, two offgas level indicating controllers were found to have excessive offsets. These controllers were repaired to correct this condition.
Cause
The fundamental condition that resulted in the manual scram was a condenser hotwell level controller that was adjusted to maintain level above the high-level alarm setpoint in the high end of the control band. During plant startup, hotwell level expectedly decreased when plant operators increased demand for reactor feedwater during power ascension. The hotwell level controller responded by transferring makeup water from the Condensate Storage and Transfer system (CST) [KA] to the hotwell. Considering the elevated level controller setpoint and its reduced response characteristics at this setting, the result was a greater quantity of water than is typically present in the condenser hotwell during a plant startup. Some of this excess water in the hotwell overflowed into the reactor feedwater pumped drain tank actuating a high level switch [JK] causing the feedwater pump trip.
The high hotwell level condition was exacerbated by the elevated setpoint of the hotwell level controller and a higher than normal water inventory available for transfer being stored in the CSTs. Both of these operational factors were implemented to accommodate the water management strategy implemented during the shutdown period. The adjustment of the hotwell level controller to the high end of the band was caused by inadequate interface requirements between normal operating conditions and strategies for shutdown water management.
Assessment of Safety Consequences
After the manual initiation of the RPS system, the subsequent operational transition to mode 4 was normal in all respects and there were no safety consequences related to the event.
Similar Events There have been no previous similar events in which an RPS actuation resulted from actions taken to implement a water management strategy.
26158 R2