Fukushima Daiichi’s Achilles Heel: Unit 4′s Spent Fuel?

Phred Dvorak – Wall Street Journal Japan April 17, 2012

Just how dangerous is the situation at Japan’s crippled Fukushima Daiichi nuclear plant? Very, according to U.S. Senator Ron Wyden, a senior member of the Senate’s energy committee who toured the plant earlier this month.

Another big earthquake or tsunami could send Fukushima Daiichi’s fragile reactor buildings tumbling down, resulting in “an even greater release of radiation than the initial accident,” Mr. Wyden warned in a Monday letter to Japanese Ambassador to the U.S. Ichiro Fujisaki.

In particular, Japan isn’t moving fast enough to remove dangerous nuclear-fuel rods from the reactors, and the U.S. should offer its help to speed things along, Mr. Wyden urged, in letters to Ambassador Fujisaki, as well as U.S. Energy Secretary Steven Chu, Secretary of State Hillary Clinton and Nuclear Regulatory Commission Chairman Gregory Jaczko.

Yoshikazu Nagai, a spokesman for Fukushima Daiichi operator Tokyo Electric Power Co. said the company couldn’t comment on the letter, and that all it can do is “proceed steadily with the (cleanup) roadmap.” Japan’s Foreign Ministry declined to comment.

Mr. Wyden’s warning touches on what some experts think is the biggest problem at the Fukushima plant: another earthquake or tsunami that exposes the least protected of its nuclear fuel to outside air.

Fukushima Daiichi suffered meltdowns at three of its reactors last year after the March 11 earthquake and tsunami knocked out power in the area. Much of the nuclear fuel in those three reactors is thought to be in a melted lump at the bottom of the vessels that surround the core. That’s bad, but at least the vessels shield the outside world from the radioactive fuel.

But Fukushima Daiichi’s Unit 4 reactor was shut down for maintenance when last year’s accident took place, meaning the nuclear fuel rods were outside those protective vessels and sitting in a pool of water, high up in the reactor building, where they were being stored. The water in that “spent fuel pool” keeps the rods cool and insulates them from the outside. But if the pool should spring a leak, or another earthquake bring the pool crashing down, all that fuel would be exposed to the outside air, letting them heat up and release massive amounts of radiation. Other reactors have spent-fuel pools too, but they contain less fuel.

Tepco says an analysis it conducted on the Unit 4 pool showed the building didn’t need reinforcing, but it went ahead and reinforced the structure anyway, increasing its safety margin by 20%. Tepco says it’s working to remove the fuel rods as fast as it can. If all goes according to its timetable, the utility could start taking the rods out in 2014.

Mr. Wyden points out, though, that the schedule allows up to ten years to get all the spent fuel in all the Fukushima reactor pools out — something he says is too risky.

“This schedule carries extraordinary and continuing risk if further severe seismic events were to occur,” he wrote in his letter to Ambassador Fujisaki. “The true earthquake risk for the site was seriously underestimated and remains unresolved.”

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  1. [...] this month Opublikowano 22 czerwca 2012 Autor: admin Fukushima Daiichi’s Achilles Heel: Unit 4′s Spent Fuel?U.S. Senator Ron Wyden, who visited Fukushima earlier this month warns of continued risks from [...]