05000397/LER-2015-007

LER-2015-007, REACTOR BUILDING PRESSURE GREATER THAN TECHNICAL SPECIFICATIONS REQUIREMENT

Columbia Generating Station
Event date:	11-09-2015
Report date:	01-07-2016
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
3972015007R00 - NRC Website

LER 15-007-00 for Columbia Regarding Reactor Building Pressure Greater Than Technical Specifications Requirement

ML16007A756
Person / Time
Site:	Columbia
Issue date:	01/07/2016
From:	Hettel W G Energy Northwest
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
GO2-16-010 LER 15-007-00
Download: ML16007A756 (4)

Plant Conditions

At the time of the event the plant was operating in Mode 1 at 100% power. The Division 1 Standby Gas Treatment (SGT) [BH] system was inoperable and unavailable due to annual system maintenance.

Event Description

On November 9, 2015 at 20:40 PST, Secondary Containment [NG] became inoperable as pressure increased above the -0.25 inches water gauge (inwg) required by Technical Specification (TS) Surveillance Requirement (SR) 3.6.4.1.1. This was due to failure of a power supply (E-E/S-299) [JX], which supplied power to the Secondary Containment Division 2 Pressure Controller (REA-DPIC-1B) [PDC]. Consequently, the Division 2 Reactor Building Exhaust Fan (REA-FN-1B) [FAN] dropped to minimum exhaust flow, and for approximately seven minutes, the Secondary Containment pressure rose above -0.25 inwg, which exceeded the TS limit.

High pressure alarms were received in the Control Room and Operators proceeded to manually start the safety related Division 2 Standby Gas Treatment [BH] lead fan (SGT-FN-1B2) [FAN] to restore negative pressure. The flow controller for this lead fan (SGT-DPIC-1B2) [PDC] also had failed as a result of the loss of power, causing its vortex damper (SGT-AD-1B2) [FAN] to remain fully open, resulting in the restoration of Secondary Containment pressure to within TS limits. The Division 1 Reactor Building Heating, Ventilation and Air Conditioning System (HVAC) [VA] was then placed in automatic mode, which maintained Secondary Containment pressure within TS limits, thus allowing Operators to manually secure SGT- FN-1B2.

During the event, there were no radioactive releases or other safety system malfunctions, other than the systems involved in the inoperability of Secondary Containment as affected by the electrical power supply failure.

Cause

Secondary Containment was lost when power supply E-E/S-299 failed. The direct cause for the loss of the power supply E-E/S-299 was an inappropriate lug size installed within the fuse block. The lug used was thicker than required for the fuse block connection and a tight mechanical connection in the lug landing area did not exist, which resulted in a loose fuse block termination. The station determined that the apparent cause of the event was a latent human performance error, in which an incorrectly sized lug was installed during initial construction. A review of the work history for E-E/S-299 showed that no work had been performed on this component after initial installation.

Immediate Corrective Action Operators manually started the Division 1 SGT lead fan to restore Secondary Containment pressure. The lead fan operated at max flow (due to the failure of E-E/S-299) resulting in the restoration of Secondary Containment pressure to within TS limits. Operators then placed Division 1 Reactor Building HVAC into automatic to maintain Secondary Containment pressure within TS limits.

A temporary alteration in support of maintenance was performed to provide temporary power while a new terminal block for E-E/S-299 was installed.

26158A R3 A condition report was initiated to document the potential degradation of critical power supplies and to ensure operability review of the potentially degraded components.

Additional Corrective Actions An extent of condition will be performed to inspect the terminations for critical power supplies located inside the Main Control Room and Remote Shutdown Room that were fused with the same style fuse block as E-E/S- 299.

Columbia currently has adequate barriers in place to prevent installation of an oversized lug. Guidance in Maintenance procedures prevents installation of an incorrectly sized lug; specifically, Maintenance procedures provide instructions on the correct way to terminate a lug connection, and instructions on terminal blocks and acceptable ways to install the terminations. Additionally, Quality Control hold points are utilized to independently verify correct installation, and Human Performance Error Prevention Tools such as pre-job briefs and procedure use/adherence are used in the field to reduce human performance errors.

Operating Experience and Previous Occurrences An extent of condition and cause review was performed for similar LERs. There have been multiple secondary containment events reported by Columbia, with several being weather-related events caused by improper tuning of the Reactor Building Outside Air differential pressure controllers. Specifically, LERs 2014-001-01 and 2013-007-01 were weather-related. LERs 2013-001-00, 2012-007-00, and 2012-003-00 describe Secondary Containment events not caused by weather. Other reported secondary containment event causes are not applicable to the current cause of an initial construction issue.

Assessment of Safety Consequences

This event resulted in an unplanned entry into LCO 3.6.4.1.A. Secondary containment pressure was greater than - 0.25 inwg for seven minutes. While the actual pressure was beyond the range allowed by Technical Specifications, the SGT system is designed to maintain Secondary Containment at a negative pressure with respect to atmosphere to minimize the release of airborne radioactive material during emergency operation.

During this event Division 2 SGT was utilized to restore Secondary Containment to TS required pressure of less than -0.25 inwg. There were no potential or actual safety consequences during this event.

This event was investigated as an event that could have prevented the fulfillment of the safety function of systems that are needed to control the release of radioactive material and mitigate the consequences of an accident, in conformance with reporting requirements in 10 CFR 50.73(a)(2)(v)(C) and 10 CFR 50.73(a)(2)(v)(D) as a result of the temporary loss of Secondary Containment. However, because it was demonstrated in this event that SGT had the ability to restore Secondary Containment pressure within the time frame allowed by the safety analysis, this event does not affect the NRC Performance Indicators. Columbia Generating Station (Columbia) reported this under Event Notification No. 51526.

Energy Industry Identification System Information Energy Industry Identification System information codes from IEEE Standards 805-1984 and 803-1983 are represented in brackets as [X] and poq throughout the body of the narrative.

26158A R3