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BRATTLEBORO -- How well prepared is= Vermont Yankee nuclear power plant to respond to an accident that cuts = off power to the plant’s spent fuel pool cooling system?
That’s a question the Nuclear Regulatory Commission will be ask= ing as part of its "lessons learned" review of the nuclear accident at F= ukushima in Japan.
In late July, the Union of Concerned Scientists suggested to the NRC = that now would be a good time to review how power plant operators would = respond to a "design basis accident" that compromises a spent fuel pool&= rsquo;s cooling system.
Earlier this month, the NRC agreed and is asking operators of power p= lants with reactors such as that at Yankee in Vernon how the plant syste= ms are capable of removing the combined heat loads, including the heat l= oad from the spent fuel pool, from the reactor building during an accide= nt.
In addition, the NRC is asking operators to prove that in a case in w= hich water in the spent fuel pool begins to boil, the additional tempera= ture, humidity and water wouldn’t affect safety systems that keep = their reactors from melting down.
"A design basis accident is something that might occur during the pla= nt’s lifetime," said David Lochbaum, director of the UCS’ Nu= clear Safety Project.
An accident such as the one at Fukushima is much worse, he said, caus= ed by conditions that were beyond what the plant was designed to withsta= nd.
The coolant system
"If you allow the pool to boil, the reactor building becomes like a s= pa or sauna," he said.
A boiling spent fuel pool can increase the heat and humidity in a rea= ctor building, which could affect safety systems, and water that condens= es from the steam could damage emergency control systems located at grou= nd level.
Much of the electrical equipment in the reactor buildings such as tha= t at Yankee is not designed to operate at high temperatures or with incr= eased humidity, he said.
Generally speaking, plants with reactors such as at Yankee have spent= fuel pool cooling systems that can’t be powered by the diesel gen= erators, which would be used to operate reactor cooling systems in case = of a loss of power from the grid.
Operators will have to tell the NRC how they are equipped to remove t= he increased heat load from their reactor buildings or how they plan to = keep their spent fuel pools from boiling in case of a design basis accid= ent.
"Mark I and Mark II containment vessels need to be provided with a re= liable means of putting water in spent fuel pools, rather than relying o= n helicopter drops and fire trucks," said Lochbaum
This issue has been simmering for at least two decades, said Lochbaum= , and it wasn’t until the Fukushima accident that the NRC agreed i= t was time to evaluate the issue, he said.
Bob Audette can be reached at raudette@reformer.com, or at 802-254-2311, ext. 160.
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