Spent Fuel Rods Drive Growing Fear Over Plant in Japan
Tomohiro Ohsumi/Bloomberg News
Reporters and Tepco workers at Reactor No. 4 at Fukushima Daiichi, which the environment and nuclear minister visited Saturday.
By HIROKO TABUCHI and MATTHEW L. WALD
Published: May 26, 2012
TOKYO — What passes for normal at the Fukushima Daiichi plant today would have caused shudders among even the most sanguine of experts before an earthquake and tsunami set off the world’s second most serious nuclear crisis after Chernobyl.
Fourteen months after the accident, a pool brimming with used fuel rods
and filled with vast quantities of radioactive cesium still sits on the
top floor of a heavily damaged reactor building, covered only with
plastic.
The public’s fears about the pool have grown in recent months as some
scientists have warned that it has the most potential for setting off a
new catastrophe, now that the three nuclear reactors that suffered
meltdowns are in a more stable state, and as frequent quakes continue to
rattle the region.
The worries picked up new traction in recent days after the operator of
the plant, Tokyo Electric Power Company, or Tepco, said it had found a
slight bulge in one of the walls of the reactor building, stoking fears
over the building’s safety.
To try to quell such worries, the government sent the environment and
nuclear minister to the plant on Saturday, where he climbed a makeshift
staircase in protective garb to look at the structure supporting the
pool, which he said appeared sound. The minister, Goshi Hosono, added
that although the government accepted Tepco’s assurances that
reinforcement work had shored up the building, it ordered the company to
conduct further studies because of the bulge.
Some outside experts have also worked to allay fears, saying that the
fuel in the pool is now so old that it cannot generate enough heat to
start the kind of accident that would allow radioactive material to
escape.
But many Japanese scoff at those assurances and point out that even if
the building is strong enough, which they question, the jury-rigged
cooling system for the pool has already malfunctioned several times,
including a 24-hour failure in April. Had the outages continued, they
would have left the rods at risk of dangerous overheating. Government
critics are especially concerned, since Tepco has said the soonest it
could begin emptying the pool is late 2013, dashing hopes for earlier
action.
“The No. 4 reactor is visibly damaged and in a fragile state, down to
the floor that holds the spent fuel pool,” said Hiroaki Koide, an
assistant professor at Kyoto University’s Research Reactor Institute and
one of the experts raising concerns. “Any radioactive release could be
huge and go directly into the environment.”
Senator Ron Wyden, Democrat of Oregon, expressed similar concerns during a trip to Japan last month.
The fears over the pool at Reactor No. 4 are helping to undermine
assurances by Tepco and the Japanese government that the Fukushima plant
has been stabilized, and are highlighting how complicated the cleanup
of the site, expected to take decades, will be. The concerns are also
raising questions about whether Japan’s all-out effort to convince its
citizens that nuclear power is safe kept the authorities from exploring
other — and some say safer — options for storing used fuel rods.
“It was taboo to raise questions about the spent fuel that was piling
up,” said Hideo Kimura, who worked as a nuclear fuel engineer at the
Fukushima Daiichi plant in the 1990s. “But it was clear that there was
nowhere for the spent fuel to go.”
The worst-case situations for Reactor No. 4 would be for the pool to run
dry if there is another problem with the cooling system and the rods
catch fire, releasing enormous amounts of radioactive material, or for
fission to restart if the metal panels that separate the rods are
knocked over in a quake. That would be especially bad because the pool,
unlike reactors, lacks containment vessels to hold in radioactive
materials. (Even the roof that used to exist would be no match if the
rods caught fire, for instance.)
There is considerable disagreement among scientists over whether such
catastrophes are possible. But some argue that whether the chances are
small or large, changes should be made quickly because of the magnitude
of the potential calamity.
Senator Wyden, whose state could lie in the path of any new radioactive
plumes and who has studied nuclear waste issues, is among those pushing
for faster action. After his recent visit to the ravaged plant,
he said the pool at No. 4 poses “an extraordinary and continuing risk”
and the retrieval of spent fuel “should be a priority, given the
possibility of further earthquakes.”
Attention has focused on No. 4’s spent fuel pool because of the large
number of assemblies filled with rods that are stored at that reactor
building. Three other reactor buildings at the site are also badly
damaged, but their pools hold fewer used assemblies.
According to Tepco, the pool at the No. 4 reactor, which was not
operating at the time of the accident, holds 1,331 spent fuel
assemblies, which each contain dozens of rods. Several thousand rods
were removed from the core just three months before so the vessel could
be inspected. Those rods, which were not fully used up, could more
easily support chain reactions than the fully spent fuel.
While Mr. Koide and others warn that Tepco must move more quickly to
transfer the fuel rods to a safer location, such transfers have been
greatly complicated by the nuclear accident. Ordinarily the rods are
lifted by giant cranes, but at Fukushima those cranes collapsed during
the series of disasters that started with the earthquake and included
explosions that destroyed portions of several reactor buildings.
Tepco has said it will need to build a separate structure next to Reactor No. 4 to support a new crane.
The presence of so many spent fuel rods at Fukushima Daiichi highlights a
quandary facing the global nuclear industry: how to safely store — and
eventually recycle or dispose of — spent nuclear fuel, which stays
radioactive for tens of thousands of years.
In the 1960s and 1970s, recycling for reuse in plants seemed the most
promising option to countries with civilian nuclear power programs. And
as Japan expanded its collection of nuclear reactors, local communities
were told not to worry about the spent fuel, which would be recycled.
The idea of recycling fell out of favor in some countries, including the
United States, which dropped the idea because it is a potential path to
nuclear weapons. Japan stuck to its nuclear fuel cycle goal, however,
despite leaks and delays at a vast reprocessing plant in the north,
leading utilities to store a growing stockpile of spent fuel.
As early as the 1980s, researchers, including those at the United States
Nuclear Regulatory Commission, started warning of the risks of storing
growing amounts of nuclear fuel in pools. The United States has since
concluded that densely packed pools are safe enough, but Tepco says that
it never even specifically studied the risks posed by the pools.
“Japan did not want to admit that the nuclear fuel cycle might be a
failed policy, and did not think seriously about a safer, more permanent
way to store spent fuel,” said Tadahiro Katsuta, an associate professor
of nuclear science at Tokyo’s Meiji University.
The capacity problem was particularly pronounced at Fukushima Daiichi,
which is among Japan’s oldest plants and where the oldest fuel
assemblies have been stored in pools since 1973.
Eventually, the plant built an extra fuel rod pool, despite suspicions
among residents that increasing capacity at the plant would mean the
rods would be stored at the site far longer than promised. (They were
right.)
Tepco also wanted to transfer some of the rods to sealed casks, but the
community was convinced that it was a stalling tactic, and the company
loaded only a limited number of casks there.
The casks, as it turns out, were the better choice. They survived the disaster unscathed.
http://www.nytimes.com/2012/05/27/world/asia/concerns-grow-about-spent-fuel-rods-at-damaged-nuclear-plant-in-japan.html?pagewanted=2&_r=1&smid=fb-share
