[FoRK] Why Fukushima made me stop worrying and love nuclear power
dmorton at bitfurnace.com
Fri Mar 25 09:07:59 PDT 2011
Tokyo (CNN) -- Authorities in Japan raised the prospect Friday of a likely
breach in the all-important containment vessel of the No. 3 reactor at the
stricken Fukushima Daiichi nuclear power plant, a potentially ominous
development in the race to prevent a large-scale release of radiation.
Contaminated water likely seeped through the containment vessel protecting
the reactor's core, said Hidehiko Nishiyama of the Japan Nuclear and
Industrial Safety Agency.
Three men working near the No. 3 reactor Thursday stepped into water that
had 10,000 times the amount of radiation typical for a nuclear plant,
Nishiyama said. An analysis of the contamination suggests "some sort of
leakage" from the reactor core, signaling a possible break of the
containment vessel that houses the core, he said.
The workers have been hospitalized, according to the agency.
Nuclear power experts cautioned against reading too much into the newest
development, saying the burns suffered by the workers may not amount to much
more than a sunburn.
Moreover, evidence of radioactivity in the water around the plant is not
necessarily surprising given the amount of water sprayed onto and pumped
into the reactors, said Ian Hutchinson, professor of nuclear science and
engineering at the Massachusetts institute of Technology.
"I am not particularly alarmed," he said.
The reactor thought to be leaking contaminated water is the same one cited
in the dramatic evacuation last week of a small crew of workers who had
stayed behind after the plant's owner pulled most employees from the area.
The workers were pulled back March 16 after white smoke began billowing from
the reactor and radiation levels spiked.
At the time, the Japanese nuclear safety agency said it suspected damage to
No. 3's containment vessel, but a government spokesman the next day said
there had been no indication of a "major breach of containment."
That reactor is of particular concern, experts have said, because it is the
only one at the plant to use a combination of uranium and plutonium fuel,
called MOX, that is considered to be more dangerous than the pure uranium
fuel used in other reactors.
Plant workers were also carefully watching the plant's No. 1 reactor,
concerned that an increase in pressure noted inside that reactor could be a
troublesome sign. Earlier, buildups of hydrogen gas had driven up pressure
that led to explosions at three of the nuclear plant's reactors, including
the No. 1 unit.
Nishiyama conceded that "controlling the temperature and pressure has been
difficult" for that reactor, which on Friday had been declared stable.
The hospitalized employees were working to reconnect power to the No. 3
reactor building when they encountered water that was about 5 inches (15
centimeters) deep. Water rushed over the boots of two workers, who received
what is called a "beta burn." The third worker had taller boots but was
hospitalized as a precaution, according to Nishiyama.
The men were exposed to the water for 40 to 50 minutes, said Tokyo Electric
Power Co., which owns the plant.
The two workers whose skin was exposed to the contaminated water had the
highest levels of radiation recorded so far, the power company said.
One, in his 30s, was exposed to 180.7 millisieverts and the other, in his
20s, tested at 179.37 millisieverts.
Nishiyama said the third man -- who was exposed to 173 millisieverts but at
first did not go to the hospital because his boots were high enough to
prevent water from touching his skin -- has also gone to the same research
hospital out of "an abundance of caution."
Beta rays given off by radioactive substances don't penetrate deeply into
materials, including flesh, said Nolan Hertel, a professor nuclear
engineering at Georgia Tech. Consequently, the danger is relatively limited,
"Basically, a beta burn would be akin to a bad sunburn," he said.
Some 17 people have been exposed to 100 or more millisieverts of radiation
since the plant's crisis began two weeks ago following a 9.0-magnitude
earthquake and subsequent tsunami struck.
A person in an industrialized country is naturally exposed to 3
millisieverts of radiation a year.
But Japan's Health Ministry recently raised the maximum level of exposure
for a person working to address the crisis at the nuclear plant to a rate of
250 millisieverts per year from the previous 100-millisievert standard.
It's not entirely clear where the contaminants in the water came from,
according to Nishiyama. But he said that based on the composition of the
radioactive material in the water, the likely source appears to be the
reactor core and not the open-air spent fuel pool onto which workers have
sprayed tons of water in recent days in an effort to keep it cool.
He said it if the water is from the reactor core, the problem may not be a
crack in containment vessel, but rather seepage from vents or valves. The
containment vessel is still holding pressure, he said, a sign that it may
not be cracked.
The incident raised questions about radiation control measures at the plant
as 536 people -- including government authorities and firefighters --
continued working there Friday, according to an official with Tokyo
The high measure prompted a top official with Nishiyama's agency to urge
Tokyo Electric to "improve its radiation management measures."
Workers are undertaking various measures to prevent the further release of
radioactive substances into the air and beyond.
Nishiyama said officials hope to start pumping in fresh water -- rather than
the corrosive seawater they have been using -- to cool the spent-fuel pool
at the No. 1 reactor and other locations.
Such pools have nuclear fuel rods that can emit radiation if the water that
normally surrounds them leaks out or boils off, which is more likely to
happen without any functional cooling system in place.
Switching to fresh water, instead of seawater, is also a priority for the
No. 2 reactor's core (as well as for its spent fuel pool), Nishiyama said.
The aim is to prevent further corrosion and damage inside, which may be
worsened by the buildup of salt.
A U.S. military barge loaded with fresh water to help cool the reactors left
Yokosuka Navy Base at 11 a.m., said Jose Schmitt, commander of Fleet
Activities at Yokosuka. A Japanese ship will escort the barge to the
Fukushima plant; U.S. personnel are not involved in the escort or
distribution of the water, according to Maj. Joseph Macri, a spokesman for
U.S. Forces Japan.
The U.S. military assistance follows a request by Japanese government and
utility authorities for large amounts of fresh water.
Beyond the seawater/saltwater issue, water in and around the Nos. 1 and 2
reactors had "high radiation levels," Nishiyama said Friday -- though not as
high as that of the No. 3 unit.
Thursday's incident has further made the latter reactor a prime focus, and
Nishiyama said Friday that "radiation levels are high" in some locales near
He said that authorities were considering "other routes" to accomplish their
goals of restarting the cooling systems around No. 3, keeping its spent
nuclear fuel pool in check and other aims. Later in the day, Nishiyama said
authorities hadn't yet determined how to get around the obstacle.
Firefighters from Tokyo and Kawasaki were expected to resume spraying toward
the No. 3 reactor and its fuel pool on Friday afternoon, according to
Efforts also continue at the Nos. 4, 5 and 6 reactors -- each of which have
their own concerns, though less pronounced because the units were on
scheduled outages when the quake struck. None of these three units had
nuclear fuel inside their reactors, though efforts are ongoing to control
temperatures inside the spent fuel pools.
On Friday morning, a concrete pump truck was used once again to inject
seawater into the No. 4 unit's fuel pool.
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