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
Dr. Robert Piccioni
www.guidetothecosmos.com
Author of "Everyone's Guide to Atoms, Einstein, and the Universe"
and "Can Life Be Merely An Accident?"
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