* NRC chairman endorses hardened vents after Fukushima visit
* Nuclear critic Markey said agency action too lenient
HOUSTON, March 19 The U.S. Nuclear Regulatory
Commission (NRC) on Tuesday delayed a decision to order
operators of more than two dozen older nuclear plants to install
filtered vents as part of the agency's post-Fukushima safety
review, according to an NRC memo posted on its website.
The commission moved forward with an order requiring
operators at 31 boiling-water reactors with Mark I and Mark II
containments - similar to the Fukushima Daiichi design - to
modify or install "hardened vents" to more effectively and
safely release excessive containment pressure after a serious
But the commission's action fell short of requiring
operators to install so-called "filtered" vents able to retain
radioactive material during severe accidents as recommended by
The NRC instead will hold a lengthy rule-making process to
further study filter options and to develop a final rule by
March 2017, six years after reactors at Fukushima were damaged
by an earthquake and tsunami.
In January, the NRC staff recommended that filters be
installed with the vents while the nuclear industry presented
less costly proposals.
The inability of operators to open vents at the Fukushima
plant led to damaging hydrogen explosions.
NRC Chairman Allison Macfarlane said her decision reflected
a recent trip to the devastated Fukushima Daiichi plant and the
"I came away from the visit with a strong conviction that
this must never happen again," Macfarlane said in a separate
"Since we have now seen first hand the results of a severe
accident at a Mark I facility, it is time to align the approach
the NRC endorsed over 20 years ago to use containment vents to
mitigate severe accidents with the actual physical capability of
those vents to operate in severe accident conditions,"
U.S. reactors with the Mark I containment design already
have hardened vents that will likely only need modification to
meet NRC requirements. But operators of the nation's eight Mark
II reactors will have to install hardened vents.
None of the 103 U.S. reactors have filtered vents.
Macfarlane also seemed to favor the addition of filters.
"Other than the additional incurred cost, there are no
substantive downsides to implementation of filters and they are
the international standard," she wrote.
Nuclear power accounts for about 20 percent of the nation's
power, but the future of nuclear power is uncertain due to
competition from low-cost natural gas-fired generation and lack
of government action to limit greenhouse gas emissions.
The commission directed the staff to look at different
filter options, including adding filters to vents or using other
Rep. Edward J. Markey, a Massachusetts Democrat and nuclear
industry critic, said the NRC "abdicated its responsibility to
ensure public health and safety" by delaying a decision on use
of filtered vents for several years.
Markey has long called for the NRC to endorse its own
technical staff's work and to quickly adopt all recommendations
made by the agency's Near Term Task Force on Fukushima,
including the use of filtered vents that would work in a severe
nuclear accident situations.
"Instead of following its top experts' safety
recommendations, it chose to grant the nuclear power industry's
requests for more studies and more delays, and even after the
study is completed there is still no guarantee that the NRC will
ever make this common sense requirement mandatory," Markey said.