It has now been determined that the explosion at the Fukushima Dai-ichi nuclear power plant some 150 kilometers north of Tokyo was actually caused by efforts to avert a meltdown, technicians having taken a calculated risk with a decision to vent radioactive steam from the severely overheated reactor Number 1. The release set off a hydrogen explosion which partially destroyed the outer turbine building. This did relieve some of the pressure that has been building up in the reactor containment core since off-site power was lost due to the earthquake, halting the flow of coolant water. But the reactor has not yet been brought under control. Four workers were injured in the explosion, and three were later hospitalized for ­radiation exposure.

Up 160 people may have now been exposed to dangerous levels of radiation, an official from the Japan Nuclear and Industrial Safety Agency told a news conference. At the same time, authorities are emphasizing that the reactor containment core has not been breached, only the wall and roof of the outer turbine building. News accounts are generally failing to make clear that the blast itself was sparked by an attempted controlled release from the reactor—which means that some radiation certainly did escape. The evacuation zone around the plant has now been expanded to a 20-kilometer radius, affecting up to 200,000 residents. Authorities are distributing potassium iodine to the evacuees and other local residents, in an effort to block their bodies' intake of the radioactive iodine isotopes released from the reactor.

The myth of "permissible levels"
Radiation levels at the site are reported to be 1,015 micro-Sieverts per hour. This is roughly equivalent to 100 millirems/hour. The allowable annual dose for members of the public from nuclear facilities in the US is 100 millirems/year, under Energy Department guidelines. In other words, hourly radiation levels around Fukushima are now at what is considered acceptable for the general public in a full year. The allowable annual dose for nuclear workers in the US is 5,000 millirems/year. The average annual background dose from all radiation sources in the US is estimated at 360 millirems/year, with 300 coming from natural sources (radon gas, cosmic rays, etc.) and 60 coming from artificial sources (power plants, medical uses, past weapons testing, etc.). The average dose from a chest X-ray is 10 millirems, and we get about 3 millirems in a cross-country flight.

Japanese and US standards are roughly equivalent, although Japanese authorities use Sieverts to measure dosages and the US uses rems. However, the US-based industry watchdog, Nuclear Information and Resource Service (NIRS), warns, "'Permissible' does NOT mean safe." Unlike curies (the per-second count of radioactive emissions) and rads (the measure of energy absorbed by tissue that is exposed to radioactivity), rems are based on an estimate—combining the amount of radiation exposure (rads) with its alleged impact on health, or "biological effectiveness," arrived at through models. The Sievert unit used in Europe and Japan equals 100 rems. States NIRS: "Since dose in rems or millirems cannot be verified, our 'legal protection standards' for workers and the public cannot be verified. These standards must be taken for exactly what they are: a myth. Unfortunately, the radiation and its likely impacts on health are real."

Reactor Number 3 in peril
The emergency cooling system has now stopped functioning at Fukushima Dai-ichi's Number 3 reactor as well, the Japan Nuclear and Industrial Safety Agency admitted after the explosion at reactor Number 1. This means that a second unit is now also in danger of overheating—and potentially, of exploding or melting down.

Faulty design spells risk for US reactors?
There are six nuclear reactors at the Fukushima Dai-ichi complex, located near the town of Okama in the Fukushima Prefecture. Another site in the same prefecture, Fukushima Dai-ni, contains four nuclear reactors. All of these reactors are owned and operated by Tokyo Electric Power Co. (TEPCO). On June 17, 2010, the same Fukushima Dai-ichi reactor Number 1 experienced a loss-of-power accident, which was fortunately brought under control by the site's back-up diesel generator.

The Fukushima reactors, among Japan's oldest and dating to the 1960s, were built by General Electric on the "Mark 1" design, using a "pressure suppression" system. Rather than being built to withstand large pressure increases, this design attempts to reduce such increases in an accident scenario. The design has been criticized by independent nuclear experts and even officials of the US Nuclear Regulatory Commission for many years.

There are 23 GE Mark 1 reactors among the 104 reactors operating at United States, including Browns Ferry, AL; Dresden, IL; Fitzpatrick, NY; Nine Mile Point 1, NY; Oyster Creek, NJ; Peach Bottom, PA; and Vermont Yankee, VT. The nuclear plant at Shoreham, on New York's Long Island, also used this design, although it was scrapped following widespread protests in 1989 before it began generating energy. Safety concerns about Mark 1 were given greater weight by the 1986 disaster at the Chernobyl plant in the USSR, which (although not designed by GE, of course) also used a "pressure suppression" system. (AP, Reuters, Reuters, Reuters, Reuters, LAT, Mirror, RIA-Novosti, Karl Grossman on CommonDreams, March 12; LAT, Nov. 16, 1986; NIRS radiation factsheet; US Energy Department radiation factsheet)

See our last post on the Fukushima disaster.

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