Japan Crisis Update: “Spent Fuel Rods Could Go Critical”

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Things are getting increasingly dicy at Japan's Fukushima Daiichi nuclear power plant: The Tokyo Electric Power Company has admitted that a nuclear chain reaction could restart if the spent fuel rods could go critical

The greatest danger comes not from the reactors, but from the spent fuel ponds, where the water level has fallen and temperatures have risen, which could result in the stored fuel rods breaking open and releasing their radioactive contents.

Japans Kyodo News reports that "Tokyo Electric Power Co. said Wednesday it is considering spraying boric acid by helicopter to prevent spent nuclear fuel rods from reaching criticality again, restarting a chain reaction, at the troubled No. 4 reactor of its quake-hit Fukushima No. 1 nuclear power plant. "The possibility of recriticality is not zero," TEPCO said as it announced the envisaged step against a possible fall in water levels in a pool storing the rods that would leave them exposed."

In Great Britain newscientist.com reports via BBC that the company is now 'caught between a rock and a hard place': "If the fuel rods are dry and hot, there could be damage to the cladding and the release of light radioactive nuclei. To prevent that, you would want to inject water. But water on its own is a neutron moderator and would enhance the chances, however small, of criticality… [water] reduces the speed of the neutrons, meaning they can be captured by uranium nuclei in the fuel rods,inducing them to split. Without water, the neutrons travel too fast, and are not captured.

"Hence the company's proposal to add boric acid, newscientist.comwhich would mop up the neutrons and hopefully stave off the reactivation of a nuclear reaction. If this did happen, it does not mean there would be a nuclear explosion, but the rods would heat up, the zirconium cladding would probably split, and the likely release of radioactive material into the atmosphere would be significantly higher."

The Daily Galaxy via Kyodo News and newscientist.com

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