Owners of almost a third of all U.S. nuclear reactors, including Exelon Corp. and Entergy Corp., were ordered to upgrade the units in the next four years to guard against pressure-induced explosions.
The Nuclear Regulatory Commission directed that operators of the 31 units, among the oldest of 104 U.S. reactors, overhaul vent systems to prevent a build-up of hydrogen and limit the rise of temperatures in containment buildings, according to a statement. The NRC’s decision adds to a 2012 order and makes fixes to the units potentially more expensive.
“Strengthened vents will help these plants continue to protect the public and the environment even if emergency systems can’t immediately stop an accident,” NRC Chairman Allison Macfarlane said today in a statement. “By safely releasing built-up pressure and hydrogen, the plants will preserve the buildings that contain radioactive material.”
The NRC is considering rules to improve U.S. safety after an earthquake and tsunami in March 2011 triggered a triple meltdown at Japan’s Fukushima Dai-Ichi nuclear power plant. The U.S. reactors covered by the agency’s decision have General Electric Co.-designed containment buildings and which are similar to the structures damaged at Fukushima.
The NRC told owners including Exelon of Chicago and Entergy of New Orleans to upgrade, starting in June 2014, the “wetwell” structures that condense steam and control pressure. By June 2017, the owners must begin installing vents for the larger “drywell” surrounding a reactor, if an analysis deems the changes necessary, according to the statement. Duke Energy Corp. of Charlotte, North Carolina, and Southern Co. of Atlanta also own units covered by the order.
“The new order is in line with the with the industry’s ideas on the most effective means to address the venting issue, and we consider the timing of the phased approach to be achievable,” Steve Kerekes, a spokesman for the Nuclear Energy Institute, a Washington-based industry group that had raised concerns about the 2012 decision, said in an e-mailed statement. “We look forward to working with the NRC and stakeholders to develop the guidance for implementation of the order.”
The ruling supersedes the March 2012 order for the 31 units to have or improve their “hardened” vents that can withstand extremely high temperatures during an accident, according to today’s statement.
“This is an improvement over the original hardened vents,” Edwin Lyman, senior scientist for the Global Security Program at the Union of Concerned Scientists, said in a phone interview. “This order is making the reliable hardened vents even harder.”
Lyman said it remains to be seen how much weight the NRC will give to reactor owners’ studies of drywells. “They want to tie up the whole issue in analysis,” he said of the industry. “It’s kind of negative regulatory creep.”
The agency in March delayed until 2017 action on a staff recommendation that the 31 reactors be equipped with radiation-scrubbing filters on the venting systems. Those changes may have cost reactor owners as much as $20 million per unit, according to industry estimates.