|Columbia Generating Station|
|Reporting criterion:||10 CFR 50.73(a)(2)(v)(C), Loss of Safety Function - Release of Radioactive Material|
10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident
|ENS 52966||10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material, 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident|
|3972017005R00 - NRC Website|
|Person / Time|
|From:||Hettel W G|
Document Control Desk, Office of Nuclear Reactor Regulation
|Download: ML17313A741 (4)|
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information Columbia Generating Station 05000- 397 2017 - 005 - 00
At the time of the event, the plant was operating in Mode 1 at 100% power. There were no structures, systems, or components that were inoperable at the start of the event that contributed to the event.
On September 12, 2017 at 1227 PDT, Operations personnel received trouble alarms for the Off Gas System [WF], Fuel Pool Cooling System [DA], and Condensate Blowdown System [SD]. A Reactor Building [NG] exhaust valve [ISV] and supply valve [ISV] closed due to a loss of power. Concurrently, station electricians called to report an electrical spark while replacing the motor control center bucket [MCC] for the Reactor Core Isolation Cooling [BN] vacuum pump [P]. For a time period of approximately one minute, Secondary Containment differential pressure increased above -0.25 inches of water gauge (inwg), resulting in Technical Specification (TS) Surveillance Requirement 220.127.116.11.1 not being met.
This event is reportable as an event that could have prevented fulfillment of safety functions needed to control the release of radiation, and mitigate the consequences of an accident per 10 CFR 50.73(a)(2)(v)(C) and 10 CFR 50.73(a)(2)(v)(D).
This condition was reported under 10 CFR 50.72(b)(3)(v)(C) and 10 CFR 50.72(b)(3)(v)(D) via Event Notification #52966 for an event or condition that could have prevented fulfillment of a safety function needed to control the release of radioactive material, and needed to mitigate the consequences of an accident.
Immediate Corrective Actions
Operations personnel took manual control of the Reactor Building exhaust air controller [DCC] and restored Reactor Building differential pressure to normal. Both the supply and exhaust valves were re-opened, and the Reactor Building exhaust air controller was then returned to automatic function.
Assessment of Safety Consequences
This event resulted in an unplanned entry into TS Action Statement 18.104.22.168.A, in which Secondary Containment pressure was greater than -0.25 inwg for approximately one minute. The peak pressure during this event was -0.18 inwg. While the actual pressure was beyond the range allowed by Technical Specifications, the purpose of maintaining a slight vacuum is to assist in drawdown of secondary containment to support accident response of the safety related Standby Gas Treatment [BH] (SGT) system. Existing engineering analysis demonstrates that for this event, the drawdown credited in Columbia's accident analysis could have been attained using either of the two available trains of the SGT system, thus there were no potential safety consequences. There was no actual safety consequence associated with this event since there was no loss of safety function and no potential for radiological release.
Cause of Event
The apparent cause of the event was that station personnel did not deliberately and conservatively perform work tasks.
Workers failed to update work instructions when work was rescheduled, and did not verify power sources at the work site.
comments regarding burden estimate to the Information Services Branch (T-2 F43), U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, or by e-mail to used to impose an information collection does not display a currently valid OMB control number, the NRC may not conduct or sponsor, and a person is not required to respond to, the information Columbia Generating Station 05000- 397 2017 - 005 - 00 Similar Events A loss of the ability to maintain Secondary Containment pressure greater than required by Technical Specifications has occurred at Columbia Generating Station four times in the past two years. One event was due to inclement weather, one event was due to degraded lubrication on a circuit breaker  fan [FAN], and two events were due to latent errors from initial construction of the plant. Energy Northwest has implemented corrective actions for these previous events.
Further Corrective Actions A Maintenance workshop will be held to strengthen understanding and knowledge of standards, and management's expectations of Maintenance personnel. Focused observations will be conducted to determine the effectiveness of the workshop. Additionally, human performance issues will be addressed.
Energy Industry Identification System (EIIS) Information codes from IEEE Standards 805-1984 and 803-1983 are represented in brackets as [XX] and [XXX] throughout the body of the narrative.