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 Japan’s needs and its loss must be not be particularly significant.

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?

Vancouver happens to have a subsiding plate directly west of its location, yet there is little evidence of major tectonic activity in the past ten thousand years.  Surely this is because Vancouver Island acts as ballast to absorb all such shocks and its west coast is practically uninhabited.  We still know little about earthquake prediction, but simple physics can isolate promising areas that will usually be safer than others it coastal building is required.

Disaster Note Fukushima

By Mikka Pineda for Roubini

This year marks Chernobyl's 25th 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.

The Fukushima 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; Chernobyl was a level 7—the only level 7 event so far.

The 1986 Chernobyl disaster, caused by design flaws and operator error, spewed radioactive graphite and clouds over Ukraine and Belarus and reached as far as Sweden. The first country to detect the emergency was Russia 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 Chernobyl, the sarcophagus will be replaced with another shell financed by a multinational fund (Ukraine is still reeling from the ongoing costs of Chernobyl 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 Belarus to be around US$235 billion—add to that another billion or two to replace the sarcophagus.

In 1979, Pennsylvania’s Three Mile Island (TMI) power plant experienced a cascade of events more similar to those of Fukushima. 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, 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 Fukushima). 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.

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 Fukushima 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.

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 Japan's power supply. If things don't get much worse, cleanup efforts and medical claims for Fukushima 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.

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