ENS 46977
ENS Event | |
|---|---|
15:14 Apr 23, 2011 | |
| Title | Invalid Primary Containment Isolation System Actuation Due to Unrecognized Design Conflict |
| Event Description | This event is reportable under 10 CFR 50.73(a)(2)(iv)(A) as an automatic actuation of general containment isolation signals affecting containment isolation valves in more than one system. This 60-day telephone notification is being made in accordance with 10 CFR 50.73(a)(1) for invalid actuations reported under 10 CFR 50.73(a)(2)(iv)(A). This actuation was invalid since it was caused by maintenance activities and not by any actual plant condition warranting containment isolation.
On April 23, 2011, at 0814 hours0.00942 days <br />0.226 hours <br />0.00135 weeks <br />3.09727e-4 months <br />, during implementation of a clearance order for ongoing work, Reactor Protection System (RPS) Bus A was transferred from the normal to alternate power supply. The power transfer functions as a break before make, and the momentary loss of power caused an unexpected actuation of the Groups 3 and 4 outboard containment isolation valves. Outboard isolations occurred in the reactor building drain and ventilation systems, and reactor closed cooling systems. Control room emergency ventilation and standby gas treatment systems also started. All systems functioned as designed, excluding those components that were already removed from service. Following the event, the RPS Bus A was re-energized and the plant was restored to normal operating condition for the current configuration per plant procedures. The unexpected actuation was due to a latent design conflict between a new design modification and existing equipment that was not discovered until during the implementation phase of the modification. The subsequent investigation cited inadequate review and engagement in the design process by station personnel of the vendor supplied design change modification package as the cause. As part of the implementation of the modification package an interposing relay was introduced into the Nuclear Steam Supply Shutoff System (NSSSS) logic circuit. The work for this modification was performed on the two days prior to this event, April 21st and 22nd. The new design was such that the source of power for the added relay was the same power supply which supplied the alternate logic channel. The resulting condition created a scenario where loss of the RPS-A power supply would complete both halves of the NSSSS outboard trip logic. The design has been revised such that loss of RPS-A or RPS-B power supply will not result in loss of both halves of the NSSSS trip logic circuit. Planned corrective actions will enhance procedures to ensure key design parameters and performance objectives are established early in the design process. There were no actual safety consequences associated with this event since all affected equipment responded as designed. The NRC Resident Inspectors have been notified. |
| Where | |
|---|---|
Columbia Generating Station  Washington (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation | |
| Time - Person (Reporting Time:+1419.43 h59.143 days <br />8.449 weeks <br />1.944 months <br />) | |
| Opened: | Rick Garcia 18:40 Jun 21, 2011 |
| NRC Officer: | Steve Sandin |
| Last Updated: | Jun 21, 2011 |
| 46977 - NRC Website
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WEEKMONTHYEARENS 566252023-05-17T10:39:00017 May 2023 10:39:00
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