05000397/LER-2017-003

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LER-2017-003, Momentary loss of Secondary Containment due to Weather
Columbia Generating Station
Event date: 6-26-2017
Report date: 8-24-2017
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
3972017003R00 - NRC Website
LER 17-003-00 for Columbia Generating Station Regarding Momentary Loss of Secondary Containment due to Weather
ML17236A455
Person / Time
Site: Columbia Energy Northwest icon.png
Issue date: 08/24/2017
From: Javorik A L
Energy Northwest
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
GO2-17-154
Download: ML17236A455 (4)


comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), 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 collection.

05000- Columbia Generating Station 397 [2017 003 00

PLANT CONDITIONS

At the time of the event, Columbia Generating Station (Columbia) was in Mode 1 operating at 98% reactor power. There were no structures, systems, or components that were inoperable that contributed to the event.

EVENT DESCRIPTION

On June 26, 2017 at 1756 PDT Secondary Containment (Reactor Building) [NG] pressure was not maintained at a vacuum greater than 0.25 inches water gauge (inwg) during a period of inclement weather. The Secondary Containment alarm was received and Secondary Containment pressure peaked at 0.08 inwg. Secondary Containment vacuum was restored to greater than 0.25 inwg by system response and operator action was not required.

EXTENT OF CONDITION

The extent of condition for Secondary Containment vacuum momentarily dropping below the required value is specific to the Reactor Building Heating Ventilation and Air Cooling (HVAC) [VA] and Standby Gas Treatment (SGT) [BH] systems, and their capability to establish and maintain Secondary Containment vacuum. No other systems were affected as a result of this condition.

IMMEDDIATE CORRECTIVE ACTION

The Reactor Building Exhaust Air (REA) flow in-service differential pressure controller (DPIC) automatically restored Secondary Containment vacuum to greater than 0.25 inwg.

CAUSE

The sudden change in wind speed and direction has been shown to cause pressure transients on the exterior walls of the Secondary Containment. When wind direction changes and wind speed increases, the auctioneering function designed into the Secondary Containment differential pressure controller will select the lowest differential pressure input. The direct cause was Secondary Containment HVAC not responding quickly enough to maintain a vacuum of greater than 0.25 inwg during a period of inclement weather.

PLANNED CORRECTIVE ACTION

The interim planned corrective action is to verify proper operation and tuning of Secondary Containment differential pressure controller.

Additionally, Energy Northwest plans to submit a license amendment request to adopt TSTF-551, Revise Secondary Containment Surveillance Requirements, to address TS 3.6.4.1 Surveillance Requirement (SR) 3.6.4.1.1.

ASSESSMENT OF SAFETY CONSEQUENCES

This event resulted in an unplanned entry into Technical Specification (TS) Action Statement 3.6.4.1 Condition A, in which Secondary Containment vacuum was less than 0.25 inwg for approximately four minutes. The peak Secondary Containment pressure during this event was 0.08 inwg. While the actual vacuum was beyond the range allowed by TS the comments regarding burden estimate to the FOIA, Privacy and Information Collections Branch (T-5 F53), 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 collection.

Columbia Generating Station 397

3. LER NUMBER

003 2017 00 05000- purpose of maintaining a slight vacuum is to assist in drawdown of Secondary Containment to support accident response of the safety related 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 Reactor Building HVAC did in fact restore Secondary Containment vacuum, and there was no loss of safety function or potential for radiological release.

PREVIOUS OCCURENCES

A loss of the ability to maintain Secondary Containment vacuum greater than required by TS has occurred at Columbia three times in the past two years as reported in LERs 2015-007-00, 2016-002-00, and 2016-003-00.

ENERGY INDUSTRY IDENTIFICATION

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.