BRATTLEBORO -- In response to the nuclear disaster at Fukushima, Japan, the U.S. Nuclear Regulatory Commission has ordered the owners of certain types of commercial nuclear reactors to make improvements to their emergency venting systems.
In an order issued on Thursday, the NRC instructed the owners of GE Mark I and Mark II Boiling Water Reactors that they have until 2019 to make the necessary improvements, but should begin the work "promptly."
Vermont Yankee nuclear power plant in Vernon is a GE Mark I Boiling Water Reactor.
"Safety is always job one and we are using the lessons learned from Fukushima to further strengthen our operations," said Jim Sinclair, spokesman for Yankee, which is owned and operated by Entergy.
In its order, the NRC noted that the events at the Fukushima Dai-ichi nuclear power plant following the March 2011 earthquake and tsunami exposed weaknesses in boiling water reactors, and that "rare natural phenomena" could overwhelm traditional built-in safety systems. The disaster at Fukushima resulted in a release of radioactive materials, which forced an evacuation of the area surrounding the plant.
"(T)he operators were unable to successfully operate the containment venting system," noted the NRC. "These problems, with venting the containments under the challenging conditions following the tsunami, contributed to the progression of the accident from inadequate cooling of the core leading to core damage, to compromising containment functions from overpressure and over-temperature conditions, and to the hydrogen explosions that destroyed the reactor buildings (secondary containments) of three of the Fukushima Dai-ichi units.
"The NRC staff performed a detailed regulatory analysis of possible improvements to Mark I and Mark II reliable hardened containment vents, including the option of installing severe accident capable vents," stated Neil Sheehan, spokesman for the NRC, in an e-mail to the Reformer.
The NRC determined that plant modifications and procedure changes were necessary to provide a "reliable hardened venting system that is capable of performing under severe accident conditions is a cost-justified substantial safety improvement. These modifications are needed to protect health and to minimize danger to life or property because they will give licensees greater capabilities to respond to severe accidents and limit the uncontrolled release of radioactive materials."
The order requires the vents be modified to handle the pressures, temperatures, hydrogen concentrations and radiation levels from a damaged reactor. The enhancements also ensure plant personnel can operate the vents safely if the reactor core is damaged.
However, the NRC is not at this time requiring plant operators to install filtration systems. NRC staff has been ordered to develop a rule for the 31 plants affected by the order "to implement strategies to enhance filtering of radioactive material from any vented gases, as well as improve procedures for preserving containment integrity."
The staff expects to hold public meetings later this month to discuss both the technical basis for the rule and the preparation of guidance for complying with the order.
"We have been reviewing the NRC decision which separated the immediate issue of venting from the longer term topic of filtering," said Sinclair. "On the venting issue, the NRC has now directed the industry to move forward with ensuring that a venting system is in place that will remain functional during severe accident scenarios."
The cost for installing hardened vents and a filtration system were estimated during hearings to be about $15 million.
"Strengthened vents will help these plants continue to protect the public and the environment even if emergency systems can’t immediately stop an accident," stated NRC Chairwoman Allison M. Macfarlane in a press release. "By safely releasing built-up pressure and hydrogen, the plants will preserve the buildings that contain radioactive material."