SALEM TWP. — A secondary containment boundary door that was left open for 6 1/2 hours at the PPL Susquehanna nuclear power plant resulted in no safety consequences, but the Nuclear Regulatory Commission said it could have been significant under an accident scenario.
The NRC said a secondary containment boundary door is “a door that leads into the large steel-reinforced concrete building that houses the reactor.”
According to PPL, the door was found ajar on Feb. 12 in the secondary containment area of the Unit 1 reactor building. PPL stated in a news release that “boundary door-612” was found propped ajar with a secondary containment boundary sign stuck in the door jamb, holding the door open.
“Upon discovery, the sign was removed from the door jamb and the door was verified closed,” the PPL release stated. “A status walk-down was performed and no other doors were found in this condition.”
Neil Sheehan, spokesman for the NRC, said that even though safety was not at risk, the situation was reportable to the NRC because it could have been significant.
“While there were no actual consequences for this door remaining open for 6 ½ hours, it could have challenged the effectiveness of a ventilation system that filters plant air prior to its release to the atmosphere and thereby ensures that there is no unfiltered pathway for radioactive gaseous releases to the environment,” Sheehan said. “It is too early to say whether the plant will face NRC enforcement action over this event. We are continuing to review the event, and that will include the more detailed report due to us within 60 days.”
PPL stated although secondary containment differential pressure was maintained throughout the time period that the door was open, the door serves as a secondary containment boundary and is required to be closed for secondary containment operability.
PPL reported the incident to the NRC as a “loss of safety function.” PPL also notified the on-site NRC resident inspector.
Sheehan said once the problem was identified, PPL immediately restored the boundary and determined that there were no issues with similar doors in the plant. He said PPL is evaluating the condition and its cause in accordance with station processes and will submit a written report to the NRC within 60 days.
“The NRC resident inspectors assigned to the Susquehanna plant on a full-time basis will review the adequacy of this report and PPL’s response once it is available,” Sheehan said. “They were notified of the problem shortly after it was identified.”
He said primary containment for the two reactors is the liner immediately around them. Secondary containment is the larger building that houses the reactors.
He said both serve as barriers to prevent the release of radioactivity as the result of a severe accident, though the integrity of primary containment is of greater importance.