Dave Lochbaum was one of nine experts testifying on emergency pressure-relief vents at an NRC hearing last Wednesday, December 9.
These vents can relieve the buildup of pressure inside the primary containment—the steel and concrete housing surrounding the reactor vessel—during an accident. The focus of the hearing was containment vents at General Electric Mark I and Mark II boiling water reactors. Five of the six reactors at Fukushima were Mark I reactors; the remaining one was a Mark II design. During the March 2011 accident in Japan, radioactive releases through the vents, which did not have filters, caused widespread contamination around the plant.
There are 23 Mark I and eight Mark II reactors in the United States. Following the recommendations of its staff following the Fukushima accident, the NRC last March issued an order requiring all of these reactors to have reliable hardened vents to allow such venting. Wednesday’s hearing was to discuss a subsequent NRC staff recommendation that those vents should be required to have filters that would reduce the amount of radioactive material released into the environment if those vents were used. The staff recommendation said:
“Based on its regulatory analyses, the staff concludes that installation of engineered filtered venting systems for Mark I and Mark II containments is the option that would provide the most regulatory certainty and the timeliest implementation. The vast majority of Mark I and Mark II severe accident sequences would benefit from a containment vent, (whether the vent includes an engineered filter or not) and the addition of an engineered filter reduces the release of radioactive materials should a severe accident occur.
“A comparison of only the quantifiable costs and benefits of the proposed modifications, if considered safety enhancements, would not, by themselves, demonstrate that the benefits exceed the associated costs. However, when qualitative factors such as the importance of containment systems within the NRC’s defense-in-depth philosophy are considered, as is consistent with Commission direction, a decision to require the installation of engineered filtered vent systems is justified.”
Dave’s slides with the comments he used for his presentation to the NRC are available here. The slides themselves are here. The NRC website includes the agenda of the hearing, with the list of speakers; the full set of slides from the presenters, and a video of the webcast.