Nuke plant has 38-hour margin for meltdown

Tokyo Electric Power Co. on Saturday released an estimate saying that if the water injections cooling its stricken Fukushima power plant are halted again, the fuel rods could start melting within 38 hours, unleashing another wave of cancerous radioactive fallout.

If the plant is hit by another quake and tsunami as powerful as the March 11 disasters, resuming water injections into reactors 1, 2 and 3 will take three hours at most, the beleaguered utility said.

The cores melted down after the plant's electricity and backup cooling pumps were knocked out by the quake and tsunami.

The estimate said the temperature of the fuel — which is believed to have solidified into a solid mass at the bottom of the pressure vessels — will rise about 50 degrees each hour until it hits its melting point of 2,200 degrees in about 38 hours.

The reactors will then start emitting massive amounts of radioactive fallout, raising levels around the premises to over 10 millisieverts — the threshold for evacuation.

Tepco, however, did not assess the likelihood of newly melted fuel leaking from the pressure vessel — which holds the core — to the containment vessel — the next layer of protection before the buildings, which are damaged.

If any component of the current makeshift water-pumping system is lost, Tepco said it can resume injections in about 30 minutes by activating emergency pumps that have been installed at an elevated position nearby. In the event of multiple functions being lost, the utility projected it will require about three hours to resume water injections.

Japan is attempting to tweak its nuclear evacuation protocol by adding a new, smaller type of danger zone, disaster minister Goshi Hosono said Saturday.

The establishment of a "precautionary action zone" during a nuclear incident would require all residents inside it to immediately leave. The PAZ would be smaller than the government's so-called emergency planning zones.

Under current disaster preparedness guidelines, the radius of the EPZ is between 8 and 10 km. This is being reviewed in light of the Fukushima crisis, which eventually forced the government to set up a no-go zone with a 20-km radius around the plant, and another advisory zone 20 to 30 km away weeks later.

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