05000266/LER-2010-004

LER-2010-004, Improper Controls for Breach of HELB Barrier

Docket Number
Event date:
Report date:
Reporting criterion:	10 CFR 50.73(a)(2)(ii) 10 CFR 50.73(a)(2)(v)(A), Loss of Safety Function - Shutdown the Reactor 10 CFR 50.73(a)(2)(ii)(B), Unanalyzed Condition
2662010004R00 - NRC Website

Event Description:

On June 25, 2010, the lock on the north control room door [DR] was replaced. This door is the normal access door to the control room [NA] and is a safe shutdown, security, and high energy line break (HELB) barrier. The door was blocked open for 24 minutes during lock replacement.

The potential consequences of a HELB event on the blocked open control room door had not been analyzed. The blocked open door could have resulted in a loss of control room functions if a HELB event had occurred during the 24-minute period the door was open.

The procedure in place at the time of the event allowed a control room HELB door to be open for no more than 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. The 12-hour time limit was not appropriate for a HELB barrier. The procedure was in the process of being revised so the door would be allowed to stay open for no more than one hour and could not be blocked open. An Operations Notebook entry was written that established interim guidance for HELB barriers pending issuance of the revised procedure. The interim action was not adequate to prevent the event.

This 60-day licensee event report is being submitted in accordance with the requirements of 10 CFR 50.73(a)(2)(ii)(8), as an unanalyzed condition, and 10 CFR 50.73(a)(2)(v)(A), and (D) as a condition that could have prevented fulfillment of the safety function of systems that are needed to shutdown the reactor and maintain it in a safe shutdown condition or mitigate the consequences of an accident. The event is classified as a safety system functional failure.

Event Analysis:

The north control room door is a HELB barrier. The door would mitigate the consequences of a potential HELB event in the turbine building by maintaining the control room operable and habitable.

Blocking this door open made the door inoperable as a HELB barrier. An inoperable HELB barrier cannot provide protection to the equipment in the room if a HELB occurs. This condition would require the equipment supported by the HELB barrier to be declared inoperable unless an evaluation was performed to determine that the equipment on the other side of the barrier would not be subject to a harsh environment.

A HELB barrier may be opened for routine ingress and egress with no effect on the HELB barrier's ability to perform its function. Since the control room door had been blocked open, the door was not open for routine ingress and egress.

Safety Significance:

During the control room door lock replacement, there was no loss of a safety-related system, structure or component. The door was blocked open for 24 minutes. The probability of a high energy line break occurring during that short time period is very low. Thus, the safety significance of the event was low.

There was no impact on the health and safety of the public as a result of this event.

Cause:

The cause of the event was a failure to communicate to station personnel the Operations notebook entry that established interim guidance for control of HELB barriers pending issuance of the revised plant procedure.

Corrective Actions:

The following corrective actions were taken:

• The permanent change to the site procedure that provides administrative controls associated with HELB barriers and doors was issued.

• An information sharing was conducted with Operations personnel on the proper use of Operations Notebook entries.

• Work instructions for replacement of control room door locks were revised to ensure that HELB barriers and doors are not blocked open.

Previous Occurrences:

None Failed Components Identified:

None