Q: How long
has contaminated water been leaking from the plant into the
Pacific?
Shunichi Tanaka, head of
Japan’s
Nuclear Regulation Authority,
has told reporters that it’s probably been happening
since an earthquake and tsunami touched
off the disaster in March 2011. (See related: "Photos:
A Rare Look Inside Fukushima Daiichi.")
According to a
report by the French Institute
for Radiological Protection and Nuclear Safety, that initial
breakdown caused,
"the largest single contribution
of radionuclides to the marine environment ever observed."
Some of that early release actually
was intentional, because TEPCO reportedly had to dump 3 million
gallons of water contaminated with low levels of radiation into
the Pacific to make room in its storage ponds for more heavily
contaminated water that it needed to pump out of the damaged
reactors
so that it could try to get them under
control.
But even after the immediate crisis
eased, scientists have continued to find radioactive
contamination in the waters off the plant.
Ken Buesseler, a senior
scientist with the Woods Hole Oceanographic Institution who has
analyzed thousands of samples of fish from the area, said he’s
continued to find the high levels of cesium-134, a radioactive
isotope that decays rapidly.
That indicates it’s still being
released.
"It’s getting into the ocean, no
doubt about it," he said. "The only news was that they
finally admitted to this."
(See related: "Photos:
Japan's Reactors Before And After.")
Q: How much
and what sort of radiation is leaking from the plant into the
Pacific?
TEPCO said Monday that
radiation levels in its groundwater
observation hole on the east side of the turbine
buildings had reached 310 becquerels per liter for cesium-134
and 650 becquerels per liter for cesium-137.
That marked nearly a 15-fold
increase from readings five days earlier, and exceeded Japan’s
provisional emergency standard of 60 becquerels per liter for
cesium radiation levels in drinking water.
(Drinking water at 300 becquerels
per liter would be approximately equivalent to one year’s
exposure to natural background radiation, or 10 to 15 chest
X-rays,
according to the World Health
Organization.
And it is far in excess of WHO’s guideline advised maximum level
of radioactivity in drinking water,
10 becquerels per liter.)
Readings fell somewhat on Tuesday. A
similar spike and fall preceded TEPCO’s July admission that it
was grappling with leakage of the radioactive water.
Scientists who have been studying
the situation were not surprised by the revelation, since
radiation levels in the sea around Japan have been holding
steady and not falling as they would if the situation were under
control.
In a
2012 study, Jota Kanda,
an oceanographer at Tokyo University of Marine Science and
Technology, calculated that the plant is leaking 0.3
terabecquerels (trillion becquerels) of cesium-137 per month and
a similar amount of cesium-134.
While that number sounds
mind-boggling, it’s actually thousands of times less than the
level of radioactive contamination that the plant was spewing in
the immediate aftermath of the disaster, estimated to be from
5,000 to 15,000 terabecquerels, according to Buesseler.
For a comparison, the atomic bomb
dropped on Hiroshima released 89 terabecquerels of cesium-137
when it exploded.
Another potential worry: The makeup
of the radioactive material being leaked by the plant has
changed.
Buesseler said the initial leak had
a high concentration of cesium isotopes, but the water flowing
from the plant into the ocean now is likely to be proportionally
much higher in strontium-90, another radioactive substance that
is absorbed differently by the human body and has different
risks.
The tanks (on the plant site) have
100 times more strontium than cesium, Buesseler said. He
believes that the cesium is retained in the soil under the
plant, while strontium and tritium, another radioactive
substance, are continuing to escape.
Q: Why is
the plant continuing to leak?
There are at least a couple of
possibilities. In an effort to cool and control the damaged
reactors, TEPCO has pumped enormous amounts of water in and out.
But that water is contaminated with
radioactive material, and it has to go someplace. According to a
recent
report issued by the
International Atomic Energy Agency, the plant operator has been
storing highly contaminated water in seven underground storage
ponds, which have a total of 60,000 tons (14.4 million
gallons/54.5 million liters) of capacity.
In April, TEPCO workers discovered
that at least three of the ponds were leaking. The IAEA
concluded that the company’s monitoring system, which hadn’t
spotted the breach, was insufficient to spot such outflow.
So it could be that the faulty
containments, which are now being replaced, are the source of at
least some of the contaminated water that’s gotten into the
ocean.
But most experts seem to think that
ordinary movement of groundwater probably is the real culprit.
An estimated 400 tons (95,860 gallons/ 362,870 liters) of water
streams into the basements of the damaged reactors each day.
Keeping that water from continuing to flow into the ocean is
crucial.
As the IAEA noted in its report,
"the accumulation of enormous
amounts of liquids due to the continuous intrusion of
underground water into the reactor and turbine buildings is
influencing the stability of the situation."
"Big surprise - water does flow
downhill," said Dr.
Janette Sherman,
a medical expert on radiation and toxic exposure who once
worked as a chemist for the Atomic Energy Commission, the
forerunner of today’s U.S. Nuclear Regulatory Commission.
"If you’ve ever had a leak in
your house during a storm, you know how hard it is to
contain water. There’s a lot of water going into the plant,
and it’s got to go someplace. It’s very hard to stop this."
Q: What can
be done to stop the leaking?
According to TEPCO’s
latest full status report on
the cleanup of Fukushima Daiichi, issued in October 2012, the
utility company already had put in place an array of measures to
try to control the radioactive water.
It built a groundwater bypass
system, which tries to siphon off and reroute groundwater
flowing down from the mountain side of the complex, before it
can get into the basements of the reactor buildings and be
contaminated. But that doesn’t seem to have made much of a dent
in the problem.
Plant workers also tried to create
an underground barrier by injecting chemicals into the soil to
solidify the ground along the shoreline of the Unit 1 reactor
building.
But TEPCO officials Tuesday said the
water was seeping under or past this barrier. Officials also
believe the water is rising to the surface, which is a troubling
development because it could hasten leakage into the sea.
The company also continues to add to
a massive tank farm on the site, with capacity to store about
400,000 tons (95 million gallons/360 million liters) of
contaminated water, and is planning to add an additional 300,000
tons of capacity over the next three years.
Unfortunately, TEPCO must deal with
an ever-increasing amount of contaminated water - nearly 150,000
tons (35.9 million gallons/136 million liters) a year - so it’s
inevitable that the company is going to run out of storage
space.
That’s why TEPCO seems to be betting
heavily on another solution - an elaborate state-of-the art
system for filtering the accumulated water and removing
radioactive materials from it. According to New Scientist, the
new system supposedly can filter out 62 different radioactive
substances.
However,
the April IAEA report noted
that the filtering system is still a work in progress, and that
in tests so far, "it has not accomplished the expected result"
in terms of removing radioactive material from the water.
Additionally, the system doesn’t
remove tritium, which isn’t as radioactive as other materials in
the water, but which still is a health hazard if it is inhaled
or ingested.
The Wall Street Journal
recently
reported that TEPCO hopes
eventually to be able to discharge the cleansed water into the
ocean, though that plan would likely meet intense opposition
from local fishermen.
Sherman, who has a chemistry
background, said she’s skeptical that such a process could work
on the enormous scale required.
"You can precipitate these
things out in the laboratory, but you’re talking about
millions of gallons here," she explained.
In a
July 26 press release, TEPCO
also said it would continue construction of a shielding wall
along the waterline, but that structure will not be finished
until September 2014.
Marine scientist Buesseler isn’t
sure that will work, either.
"You can build a dam, but
eventually the water goes around it," he explained.
Q: How far
is the radiation spreading, and how fast does it travel?
The initial gigantic deluge of
contaminated water dispersed through the immediate Fukushima
coastal area very quickly, according to a
2012 report by the American
Nuclear Society.
But it takes years for the
contamination to spread over a wider area. A mathematical model
developed by Changsheng Chen of the University of Massachusetts
at Dartmouth and Robert Beardsley of the Woods Hole
Oceanographic Institute found that radioactive particles
disperse through the ocean differently at different depths.
The scientists estimated that in
some cases,
contaminated seawater could reach the
western coast of the United States in as little as
five years.
Buesseler thinks the process occurs
a bit more rapidly, and estimates it might take three years for
contamination to reach the U.S. coastline.
Q: What are
the potential risks to humans, and who might be affected by the
contamination?
This is a murky question, because
it’s not that easy to determine whether health problems that may
not show up for decades are caused by exposure to radioactive
contamination.
A
report released in February by
the World Health Organization, which was based upon estimates of
radiation exposure in the immediate wake of the accident,
concluded that it probably would cause "somewhat elevated"
lifetime cancer rates among the local population.
But figuring out the effect of years
of exposure to lower levels of radioactive contamination leaking
into the ocean is an even more complicated matter.
Minoru Takata, director of
the Radiation Biology Center at Kyoto University, told the
Wall Street Journal that the radioactive water doesn’t pose
an immediate health threat unless a person goes near the damaged
reactors. But over the longer term, he’s concerned that the
leakage could cause higher rates of cancer in Japan.
Marine scientist Buesseler believes
that the leaks pose little threat to Americans, however.
Radioactive contamination, he says,
quickly is reduced "by many orders of magnitude" after it moves
just a few miles from the original source, so that by the time
it would reach the U.S. coast, the levels would be extremely
low.
Q: Will
seafood be contaminated by the leaks?
As Buesseler’s
research has shown, tests of
local fish in the Fukushima area still show high enough levels
of radiation that the Japanese government won’t allow them to be
caught and sold for human consumption - a restriction that is
costing Japanese fishermen billions of dollars a year in lost
income.
(But while flounder, sea bass, and
other fish remained banned for radiation risk, in 2012 the
Japanese government
did begin allowing sales of octopus and
whelk, a type of marine snail, after tests showed no
detectable amount of cesium contamination.)
Buesseler thinks the risk is mostly
confined to local fish that dwell mostly at the sea bottom,
where radioactive material settles. He says bigger fish that
range over long distances in the ocean quickly lose whatever
cesium contamination they’ve picked up.
However, the higher concentration of
strontium-90 that is now in the outflow poses a trickier
problem, because it is a bone-seeking isotope.
"Cesium is like salt - it goes
in and out of your body quickly," he explains. "Strontium
gets into your bones."
While he’s still not too concerned
that fish caught off the U.S. coast will be affected,
"strontium changes the equation
for Japanese fisheries, as to when their fish will be safe
to eat."
