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Japanese Nuclear Crisis - Do We Need to
Worry?
by Robert Piccioni
March 22, 2011
The
recent earthquake and tsunami off Japan have created a nuclear reactor
crisis that concerns everyone. I’ve asked my friend and fellow
Osher instructor Dr. Jerry Clifford to provide his insight and answer
questions that many are asking. Jerry is a Ph.D. physicist and
expert in nuclear energy plants. What follows is a collaborative effort.
What caused the
nuclear reactor crisis?
The earthquake did no
significant damage to the reactors, which shut down properly following
the shaking. Even when reactors are “off”—no longer producing
electricity—they still have to be cooled. Nuclear reactors create
heat by fission, breaking uranium nuclei into smaller nuclei called
fission products. These fission products are radioactive and
continue to produce heat, diminishing rapidly at first, then more
gradually over decades.
The earthquake
disrupted the electric power grid, cutting power to the water pumps
that cool the reactors. Emergency diesel generators immediately
started to keep the pumps running. But when the tsunami hit about
ten minutes later, the generator building flooded, shutting off power
to the pumps. Emergency back-up batteries were engaged, but ran
out after several hours. After that, there was no cooling for the
reactors.
Water in the reactors
and the spent-fuel cooling pools heated up and ultimately boiled into
steam, leaving the fuel exposed to air. Steam (H2O) decomposed,
oxidizing the fuel rod casings, leaving hydrogen gas, which
exploded—remember the Hindenburg?
The remedy is to cool
the fuel rods with water as rapidly as possible. This is difficult
because the exposed fuel rods have increased radiation within the
facility to dangerous levels. Water cannons are being used to
fill the cooling pools, hoping to eventually cover the rods and provide
shielding to protect the workers. Boron is being added to the water to
absorb free neutrons thus reducing further nuclear reactions.
How serious is the
situation and how bad can it get?
The situation is very
serious because hydrogen and/or steam explosions could rupture the
containment vessels, which are still believed to be essentially intact
and which prevent radiation escaping the facility and becoming
airborne, as happened in Chernobyl.
If the reactor or
pools dry out and sufficient heat is generated, then, hypothetically
the fuel rods could melt into a liquid and restart the fission process,
as in an operating reactor. This would increase the problem
immensely with huge amounts of radiation. The scenario is scary
but improbable.
The facility
operators are trying to restore electrical power to the pumps, hoping
these will be operable, but no one currently knows the exact extent of
damage caused by the explosions and tsunami.
What are the
health dangers?
The main danger is
radiation from aerosolized fission products. As of March 18,
2011, the radiation levels were only high within the facility.
Monitoring is also ongoing at many places, both near the reactors and
throughout Japan. Current radiation readings are available at
http://www.mext.go.jp/english/. Luckily, the winds are generally
off shore taking any effluents out over the Pacific.
Only a barely
detectable level of radiation has reached California. Our
Department of Energy reports that radiation levels in Sacramento are
elevated by one-millionth of the normal background—a testament to the
precision of their instruments. Any radiation plume will be greatly
diminished by our distance from Japan. The EPA is monitoring
radiation levels along the coast; see http://www.epa.gov/japan2011/.
There is no need to
do anything now. If you want to worry, worry about driving to the
supermarket because that is much more dangerous than the radiation from
Japan.
Radiation Levels
and Backgrounds
The Japanese reactors
are inherently safer than the Chernobyl reactor. Chernobyl had no
containment vessel and used graphite for cooling rather than
water. The graphite caught fire and quickly spread radioactive
fission products, killing about 50 workers almost immediately. An
official international investigation concluded that 150,000 people were
exposed to over 20 times normal background radiation from Chernobyl,
which might result in 4,000 premature deaths (this number is strongly
contested).
Everyone on Earth is
exposed to background radiation; on average each of us gets 2.4
millisieverts (mSv) per year. About half of that is from radon gas
seeping up from the ground and being trapped within our buildings. We
also get 0.5 mSv from radioactive elements in the ground, 0.4 mSv from
cosmic rays from outer space, and 0.3 mSv from food. Man-made
radiation, from past nuclear weapons testing, nuclear power plant
operations and accidents (almost entirely Chernobyl) add 0.005 mSv, on
average.
However, background
radiation varies greatly. Those in well-insulated buildings can get up
to 4 times the normal dose, as do people in Denver, with less
atmosphere shielding them from cosmic rays. And, in Ramsar, Iran,
radiation levels are 200 times normal. Yet, residents of Denver and
Ramsar show no adverse health effects.
Flying also increases
radiation exposure (particularly polar routes): one round trip between
New York and Tokyo boosts your dose by 0.2 mSv. And eating a banana
every day will boost your annual dose by 30 mSv, over 12 times normal,
due to the potassium in bananas. Our bodies need potassium, but it is
radioactive, as is the carbon in everything we eat.
Medical procedure can
also expose us to radiation. With modern equipment and properly trained
staff, a chest x-ray delivers 0.02 mSv, dental x-rays deliver 0.003
mSv, and a CT chest scan delivers 7 mSv.
Life is Risky
We all want our loved
ones and ourselves to be safe, but the reality is that the world is
full of risks.
In 2008, 37,261
people died in motor vehicle accidents in the U.S. (much lower than
many prior years) — yet we drive. Do we really have a choice?
Our society consumes
vast amounts of energy, and wherever that energy is produced or stored
there will be life-threatening risks. The BP oilrig explosion in the
Gulf killed 11 workers, and a BP refinery explosion in Texas killed 15.
No one has ever died due to a commercial nuclear reactor accident in
the U.S.
According to Dana
Christensen, associate director of Oak Ridge National Lab, the
effluent from burning coal releases 100 times as much radiation into
the biosphere as does a nuclear reactor producing the same amount of
energy.
When the final grim
statistics are reported, the number of Japanese killed by the
earthquake, the tsunami, and by the explosions and fires from gas
systems will probably be hundreds of times higher than the number lost
due to their nuclear reactors.
Yes, we can and
should do better. Year-by-year technology advances and step-by-step we
reduce those risks that we can. That effort will proceed more
effectively if we are rational about our risks and our options.
Hysteria promotes media revenue, but not good public policy.
Best Regards,
Robert
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Dr Robert
Piccioni,
Author of "Everyone's
Guide to Atoms, Einstein, and the Universe"
and "
Can Life Be
Merely An Accident?"
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