NRC Validates Oyster Creek Severe Accident Venting Strategy

Jun 28, 2017

The Nuclear Regulatory Commission approved severe accident venting plans at the Oyster Creek Nuclear Generating Station while relaxing its mandated enhancements to boiling water reactors for reliable hardened vents to manage the aftermath of such an event. The approval comes after Exelon Corp., the Illinois-based utility company that owns and operates the nuke plant, requested the relaxation of orders.

“The NRC staff evaluated Exelon’s proposed venting strategy, and associated water management guidance,” William M. Dean, director of the NRC’s Office of Nuclear Reactor Regulation, wrote in a June 20 letter to Exelon officials,” and concluded that the guidance and containment venting strategy, including preservation of the containment wetwell vent path, will make it unlikely that Oyster Creek would need to vent from the containment drywell during severe accident conditions, or during an extended loss of alternating current power event.”

The order to enhance nuclear power plants like Oyster Creek came in the aftermath of the Fukushima incident in March 2011, making reliable hardened vents from both the wetwell – the torus, or doughnut-shaped reservoir of cooling water at the base of the reactor building – and the drywell, which encloses the reactor, mandatory.

“The difference between our reliable hardened vent order and the existing vent system at Oyster Creek has to do with compliance with certain specifications in our order, specifically having to do with the hardware,” said Neil Sheehan, NRC public affairs officer for Region 1. “The company successfully argued it will have venting strategies in place to cope with a severe accident.”

Sheehan said the probability of a severe accident at the plant is remote, especially given the limited amount of operational life left at the Lacey Township-based facility. Exelon notified the NRC on Jan. 7, 2011 of its intention to permanently shut down Oyster Creek no later than Dec. 31, 2019. The company subsequently asked the NRC for relaxation of the reliable hardened vent order for the nuke plant. The extension request was based on the limited remaining operational time for the plant, existing plant safety features, existing containment vent enhancements to address venting under severe accident conditions, and FLEX equipment and strategies put in place at the plant under a separate NRC post-Fukushima requirement, he said.

“What’s more, the post-Fukushima addition of portable generators and pumps at the plant, the development of accident response strategies and other factors give us reasonable assurance that the plant will remain safe,” Sheehan said, adding Oyster Creek has a hardened containment vent system that can be used during a severe accident to limit reactor containment building pressurization.

That system is intended to be used as one element of the plant’s reactor core damage prevention strategies. Other elements include safety-grade isolation condensers that are specifically designed to remove decay heat from the reactor vessel following a loss of power and FLEX equipment acquired by the site after Fukushima, according to Sheehan. FLEX equipment includes portable generators and pumps that could be used in the event that all off-site power to the plant is lost. Power to emergency diesel generators and emergency batteries on-site would also need to be lost for the FLEX equipment to work.

“In other words, Oyster Creek has a plan for dealing with a severe accident even though it will not fully comply with our reliable hardened vent order,” Sheehan said.

The base-load nuclear generating station is a single unit boiling water reactor, located on 800 acres along neighboring Oyster Creek. It first came online in December 1969. It is licensed to operate through April 9, 2029, but is slated to come offline permanently Dec. 31, 2019.

— Gina G. Scala

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