SOMA, Japan (AP) — Water levels dropped precipitously Monday inside a stricken Japanese nuclear reactor, twice leaving the uranium fuel rods completely exposed and raising the threat of a meltdown, hours after a hydrogen explosion tore through the building housing a different reactor.
Water levels were restored after the first decrease
but the rods remained exposed late Monday night after the second episode,
increasing the risk of the spread of radiation and the potential for an
eventual meltdown.
The cascading troubles in the Fukushima Dai-ichi
plant compounded the immense challenges faced by the Tokyo government, already
struggling to send relief to hundreds of thousands of people along the
country's quake- and tsunami-ravaged coast where at least 10,000 people are
believed to have died.
Later, a top Japanese official said the fuel rods
in all three of the most troubled nuclear reactors appeared to be melting.
Of all these troubles, the drop in water levels at
Unit 2 had officials the most worried.
"Units 1 and 3 are at least somewhat
stabilized for the time being," said Nuclear and Industrial Agency
official Ryohei Shiomi "Unit 2 now requires all our effort and
attention."
In some ways, the explosion at Unit 3 was not as
dire as it might seem.
The blast actually lessened pressure building
inside the troubled reactor, and officials said the all-important containment
shell — thick concrete armor around the reactor — had not been damaged. In
addition, officials said radiation levels remained within legal limits, though
anyone left within 12 miles (20 kilometers) of the scene was ordered to remain
indoors.
"We have no evidence of harmful radiation
exposure," deputy Cabinet secretary Noriyuki Shikata told reporters.
On Saturday, a similar hydrogen blast destroyed the
housing around the complex's Unit 1 reactor, leaving the shell intact but
resulting in the mass evacuation of more than 185,000 people from the area.
So the worst case scenario still hung over the
complex, and officials were clearly struggling to keep ahead of the crisis.
Late Monday, the chief government spokesman said
there were signs that the fuel rods were melting in all three reactors, all of
which had lost their cooling systems in the wake of Friday's massive earthquake
and tsunami
"Although we cannot directly check it, it's
highly likely happening," Chief Cabinet Secretary Yukio Edano told
reporters.
Some experts would consider that a partial
meltdown. Others, though, reserve that term for times when nuclear fuel melts
through a reactor's innermost chamber but not through the outer containment
shell.
Officials held out the possibility that, too, may
be happening.
"It's impossible to say whether there has or
has not been damage" to the vessels, nuclear agency official Naoki Kumagai
said.
If a complete reactor meltdown — where the uranium
core melts through the outer containment shell — were to occur, a wave of
radiation would be released, resulting in major, widespread health problems.
The Monday morning explosion at the Fukushima
Dai-ichi plant's Unit 3 injured 11 workers and came as authorities were trying
to use sea water to cool the complex's three reactors.
While four Japanese nuclear complexes were damaged
in the wake of Friday's twin disasters, the Dai-ichi complex, which sits just
off the Pacific coast and was badly hammered by the tsunami, has been the focus
of most of the worries over Japan's deepening nuclear crisis. All three of the
operational reactors at the complex now have faced severe troubles.
Operators knew the sea water flooding would cause a
pressure buildup in the reactor containment vessels — and potentially lead to
an explosion — but felt they had no choice if they wanted to avoid complete
meltdowns. Eventually, hydrogen in the released steam mixed with oxygen in the
atmosphere and set off the two blasts.
Japan's meteorological agency did report one good
sign. It said the prevailing wind in the area of the stricken plant was heading
east into the Pacific, which experts said would help carry away any radiation.
Across the region, though, many residents expressed
fear over the situation.
People in the port town of Soma had rushed to
higher ground after a tsunami warning Monday — a warning that turned out to be
false alarm — and then felt the earth shake from the explosion at the Fukushima
reactor 25 miles (40 kilometers) away. Authorities there ordered everyone to go
indoors to guard against possible radiation contamination.
"It's like a horror movie," said
49-year-old Kyoko Nambu as she stood on a hillside overlooking her ruined
hometown. "Our house is gone and now they are telling us to stay indoors.
"We can see the damage to our houses, but
radiation? ... We have no idea what is happening. I am so scared."
Meanwhile, 17 U.S. military personnel involved in
helicopter relief missions were found to have been exposed to low levels of
radiation after the flew back from the devastated coast to the USS Ronald
Reagan, an aircraft carrier about 100 miles (160 kilometers) offshore.
U.S. officials said the exposure level was roughly
equal to one month's normal exposure to natural background radiation, and the
17 were declared contamination-free after scrubbing with soap and water.
As a precaution, the U.S. said the carrier and
other 7th Fleet ships involved in relief efforts had shifted to another area.
While Japan has aggressively prepared for years for
major earthquakes, reinforcing buildings and running drills, the impact of the
tsunami — which came so quickly that not many people managed to flee to higher
ground — was immense.
By Monday, officials were overwhelmed by the scale
of the crisis, with millions of people facing a fourth night without
electricity, water, food or heat in near-freezing temperatures.
International scientists say there are serious
dangers but little risk of a catastrophe like the 1986 blast in Chernobyl,
where there was no containment shells.
And, some analysts noted, the length of time since
the nuclear crisis began indicates that the chemical reactions inside the
reactor were not moving quickly toward a complete meltdown.
"We're now into the fourth day. Whatever is
happening in that core is taking a long time to unfold," said Mark Hibbs,
a senior associate at the nuclear policy program for the Carnegie Endowment for
International Peace. "They've succeeded in prolonging the timeline of the
accident sequence."
He noted, though, that Japanese officials appeared
unable to figure out what was going on deep inside the reactor. In part, that
was probably because of the damage done to the facility by the tsunami.
"The real question mark is what's going on
inside the core," he said.
Overall, more than 1,500 people had been scanned
for radiation exposure in the area, officials said.
Yamaguchi reported from Tokyo. Associated Press
writers Tim Sullivan in Bangkok contributed to this report.
Copyright
2011 The Associated Press.
(AP
Photo/Kyodo News)
