Thursday, March 17, 2011
Fukushima Compared to TMI and Chernobyl
This item places the present disaster in proper perspective and eliminates a couple of issues.
First the reactors are now well on the way to cooling down to safe levels, though just like TMI, partial melts in the core caused immense damage. However, we can expect three of the reactors to be taken apart almost routinely or at least mostly so. One however is likely suffering from a lot of fused metal and will not be routine.
Second, the pleasant surprise is that the plant itself was literally a month from decommissioning which explains the lack of proactive steps after the danger report two years ago, or rather the action was the planned shutdown and decommissioning. We just got unlucky.
Third, the plant was thus surplus to
needs and its loss must be not be particularly significant. Japan
The tsunami risk was not properly planned for and why this should be so escapes me. All reactors need to be evaluated for this obvious risk. At the least critical back up power can easily be installed in an upper floor of a stout building emplaced behind the reactors.
All plants of this nature should be located behind barrier islands. Please observe, the quake took place many miles from shore, yet the effects on land only affected severely the coastal area of
Honshu. Did anyone notice on the west coast?
By Mikka Pineda for Roubini
This year marks
anniversary, and how ironic it is that the world has a new nuclear emergency on
its hands: Japan's Fukushima power plant, operated by TEPCO. The
situation at Fukushima continues to
worsen, with explosions at two more reactors and the radiation released
surpassing that of Three Mile Island. The
40-year-old reactors, designed by General Electric, were due for
decommissioning at the end of this month.
nuclear incident will likely be upgraded from a level 4 to a 5 on the
International Nuclear and Radiological Event Scale. The scale runs from 0 to
7—the most severe. The incident will remain "an event with local
consequences," although this excludes the consequences for the expansion
of nuclear power generation around the world. Three Mile
Island was a level 5; Fukushima
was a level 7—the only level 7 event so far. Chernobyl
Chernobyl disaster, caused
by design flaws and operator error, spewed radioactive graphite and clouds over
Ukraine and Belarus and reached as far as .
The first country to detect the emergency was Sweden which, in its
pre-Glasnost days, neglected to notify the world and did not begin evacuation
until 36 hours after the first explosion. Firefighters and liquidators (cleanup
workers) were inadequately informed about and equipped for the dangers they
were facing. The cleanup took decades and is not over yet—180 tons of
radioactive material remains sitting in a concrete sarcophagus over the plant.
The sarcophagus cracked last year and is emitting radioactive gases. In 2011,
the 25th anniversary of Russia Chernobyl, the
sarcophagus will be replaced with another shell financed by a multinational
fund (Ukraine is still reeling from the ongoing costs of and lacks
enough funds to replace the shell alone). The total cost of resettling
inhabitants, cleaning and sealing the area and paying off medical claims is
estimated by Chernobyl
to be around US$235 billion—add to that another billion or two to replace the
Pennsylvania’s Three Mile
Island (TMI) power plant experienced a cascade of events more similar to those
TMI was a pressurized water reactor; Fukushima
was a boiling water reactor. There's little difference between the two
insofar as both used water to cool and regulate the reactors, except that TMI
had a pressurizer. Like Fukushima Fukushima, Three Mile
Island Unit 2 (TMI-2) was vented into the air to reduce pressure in the core,
releasing some fissile products (Cesium-137 and Iodine-131—the same
products released from ).
TMI-2 also experienced a small hydrogen explosion, which tore off the exterior
walls of the containment building, and a partial core meltdown. Cleanup cost
US$975 million and took 14 years to complete. Fukushima
The problem with light water reactors in general is the vicious cycle of needing to vent coolant to relieve pressure and then having less to cool the core, which progressively generates more heat and pressure that then needs to be relieved. If the core heats up enough, the zirconium cladding around the core causes the water to release hydrogen. The hydrogen builds up outside the reactor vessel, eventually causing the exterior walls of the containment building to explode.
Add to this the problem with
in particular, which is that once the main power supply (the nuclear plant) is
shut off—in this case because the earthquake triggered an automatic shutdown—the reactors
still need an alternative power supply to run thecooling systems. Fukushima 1's
batteries last only eight hours, and the emergency diesel generators lasted
only a total of 24 hours. Fukushima
Now that the core is damaged and seawater has been poured over the reactors to cool them,
Fukushima 1 (and possibly
a plant in Tokai as well) are damaged beyond repair—resulting in a permanent
loss in 's
power supply. If things don't get much worse, cleanup efforts and medical
claims for Japan
will be similar to those of TMI. The radiation exposure of the civilian
population so far remains light, and iodine tablets were promptly distributed
to counteract any radioactive iodine released. Though those tablets
only prevent thyroid cancer, so far only around 8,000 microsieverts have
been detected outside the plant—far below the one sievert minimum
for radiation sickness. Fukushima