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I cite from the wiki en.wikipedia.org : "The low-pressure coolant injection system, the "heavy artillery" in the ECCS (emergency core cooling system, ed.), can be operated at reactor vessel pressures below 465 psi. The LPCI consists of 4 pumps driven by diesel engines, and is capable of injecting a mammoth 150,000 L/min (40,000 US gal/min) of water into the core. Combined with the CS (core sprayers, ed.) to keep steam pressure low, the LPCI is designed to suppress contingencies by rapidly and completely flooding the core with coolant."

Nuclear minister eyes standards for reactors' lifespan Goshi Hosono, Japanese minister tasked with handling the country's nuclear crisis, said Sunday that the government needs to set definitions and standards for how long existing nuclear power reactors should be allowed to operate before they are decommissioned. mdn.mainichi.jp

1988 study: www.annals.org
Insignificant risk of fatalities, major radiation release once per 100,000 years, fuel damage per 10,00 years.
the risk for acute fatalities is statistically insignificant (less
than 1 X 10~2 per year) and the risk of latent fatalities is less than
other societal risks (on the order often or less per year) (8). The
latter risk is also statistically small when compared with the normal
cancer rate.


Over a spectrum of reactor types, the frequency of a core melt
accident is estimated to be less than 1 X 10-4 per year (once in 10
000 years) (8). Also, not all core melt accidents lead to breach of
containment, with subsequent public health and economic consequences.
Because no American or European containment has ever failed due to a
core-melt accident (Chernobyl did not have a conventional
containment), we can only estimate the conditional probability of
failure. Depending on containment type, this probability has been
estimated to range from 0.01 to 0.90, with a best estimate of 0.1 (8).
The probability of a major release of radioactivity from a nuclear
plant in the United States is thus thought to be less than 1 in 100
000 years (8).

The probability of a core melt had been estimated at about one chance in 10,000 reactor years of operation, he said. "We've had now three core melts in 30 years in less than 500 reactors, he said, referring to Three Mile Island, Chernobyl and now Japan. "So the probability of a partial core melt is one chance in several hundred instead of one chance in 10,000. So, it's not a good statistic." articles.cnn.com CNN

Tochigi moving radioactive ash to 6 sewage plants

Tochigi Prefecture, northeast of Tokyo, has begun moving radioactive sludge from a temporary storage site to several sewage plants, where it can only be kept for the time being.

Following the accident at the Fukushima Daiichi nuclear plant, high levels of radioactive material were detected in sludge at waste water plants across eastern Japan.

Tochigi Prefecture had incinerated the sludge from its sewage plants at its waste water recycling plant, and melted the ash to reduce its volume. But the amount of ash has reached 1,000 tons, close to the storage capacity.
www3.nhk.or.jp
To deal with the problem, the prefecture decided last month to keep the radioactive waste at 6 of its waste water treatment plants.

On Monday, 50 tons of contaminated ash was being delivered by truck to a sewage plant in Kaminokawa Town. The ash contains around 30,000 becquerels of radioactive cesium per kilogram.

Tochigi Prefecture says the ash will pose no health hazards to residents or the environment, because it will be covered with water-proof sheets and stored at sites more than 20 meters from the nearest houses.

But the head of a local residents' group says that although they have agreed to the storage, they still have doubts about safety. He said he wants the authorities to be clear about how long they intend to keep the waste at the sewage plants.