The situation at Fukushima continues to worsen, with now 2 more reactors experiencing cooling problems and the radiation released so far surpassing that of Three Mile Island. General Electric designed the troubled, 40-year old reactors, which were due for decommissioning at the end of this month.
The Fukushima nuclear incident will likely be upgraded from level 4 to a 5 on the International Nuclear and Radiological Event Scale (INES). The scale runs from 0-7, with 7 being the most severe. It will remain “an event with local consequences” – although this doesn’t count the consequences for the spread of nuclear power generation around the world. Three Mile Island was a level 5. I doubt Fukushima will be as bad as Chernobyl, which was a level 7 event – and the only level 7 event so far.
Chernobyl (1986) was caused by design flaws and operator error, spewing radioactive graphite and clouds all over Ukraine, Belarus and reaching as far as Sweden – the first country to detect something was up was Russia, who, in its pre-Glasnost days, didn’t care to notify the world. The Russians did not begin evacuation until 36 hours after the first explosion. Firefighters and liquidators (clean-up workers) were inadequately informed/equipped about the dangers they were facing. Cleanup took decades and is not over yet. There was never a cleanup in terms of fuel disposal – 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 $235 billion. Add to that another billion or two to replace the sarcophagus.
Three Mile Island (1979) experienced a cascade of events more similar to Fukushima. 3 Mile was a PWR (pressurized water reactor). Fukushima was a BWR (boiling water reactor). There’s little difference between the two insofar as both used water to drive turbines, except that 3 mile 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 during Fukushima). TMI-2 also experienced a small hydrogen explosion that tore off the exterior walls of the containment building as well as a partial core meltdown. Supposedly the released radiation did not raise cancer incidence in the area. Cleanup cost $975 million and took 14 years to complete. TMI-1 will continue to operate until decommissioning in 2034.
The problem with light water reactors in general is the vicious cycle between venting off coolant to relieve pressure but then having even less coolant to cool the core, hence generating more heat and pressure that needs to be relieved somehow. 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. (A basic containment building contains a reactor vessel where fission occurs, turbines driven by the heat generated by the fission, and a cooling system).
Add to this the problem with Fukushima in particular, which is that once the main power supply (the nuclear plant) is shut off (earthquakes tripped the automatic shutdown – sort of like circuit breakers in your home), the reactors still need an alternative power supply to run the cooling systems. Fukushima 1’s batteries last only 8 hours and the emergency diesel generators brought in lasted only a total of 24 hours.
Longer term impact:
Once the core is damaged and seawater is poured over reactors to cool them, Fukushima 1 (and possibly a plant in Tokai as well) will be useless beyond repair – hence a permanent loss in Japan’s power supply. If things don’t get much worse, I think cleanup efforts and medical claims for Fukushima will be similar to that of Three Mile. 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 1,557 micro Sieverts have been detected outside the plant – far below the 1 Sievert minimum for radiation sickness.