Tokyo Electric Co.: Chance of chain reaction ‘not zero’

Japan nuclear crisis: Is massive water dump making any difference?

Peter Grier
Christian Science Monitor
March 18, 2011

As Japan races against time to control its nuclear crisis, the cooling pools for the spent fuel rods at the Fukushima nuclear plant remain a source of major concern. On Friday water levels in at least one pool – housed in the Unit 3 reactor building – were dangerously low, according to Japanese authorities.

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The bad news is that enough fuel rods remain in the pools that, if exposed to air for a long enough period of time, it is theoretically possible that they could burn and melt into a pile of fissile rubble dense enough to restart a nuclear chain reaction.

Tokyo Electric Power said earlier this week that the possibility of such “recriticality” occurring in the pools is not zero. If it happened the pools would then in essence have turned into running mini-reactors, and begin emitting much more heat and dangerous radiation.

Pouring water laced with boron into a pool would help stop such a reaction, as boron absorbs neutrons which are emitted during a nuclear reaction. Japan on Thursday announced plans to import 150 tons of boron from South Korea and France to replenish its stocks.

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Nuclear update: Entire reactor core stored in fuel pond

Zena Iovino
New Scientist
March 18, 2011

Japan has raised the accident level at the Fukushima Daiichi nuclear power plant to 5 on an international scale of 7, according to the Kyodo news agency and NHK. The partial meltdown at Three Mile Island in 1979 also ranked as a level 5. But there was some good news.

The International Atomic Energy Agency (IAEA) said on Friday that the situation at reactors 1,2 and 3 appears to remain fairly stable. The spent-fuel ponds at units 3 and 4, however, remain an important safety concern. Reliable, validated information is still lacking on water levels and temperatures at the spent fuel ponds, but the IAEA announced on Friday that prior to the earthquake,

The entire fuel core of reactor Unit 4 of the Fukushima Daiichi nuclear power plant had been unloaded from the reactor and placed in the spent fuel pond located in the reactor’s building.

This would explain the fear yesterday that the spent fuel in the Unit 4 pond could go critical (see 18:20, 16 March update, below).

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This article was posted: Friday, March 18, 2011 at 5:54 pm

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