sabato 30 novembre 2013

Japan Expert: “All I can do is pray nothing goes wrong” at Fukushima Unit 4; Concern over “dangerous chain of events” — TV: “At least evacuate nearby residents” — NYTimes: No external supervision of Tepco; To start within 10 days 

New York Times, Nov. 10, 2013:
The Process
[...] In the next 10 days [Tepco] is set to start the delicate and risky task of using a crane to remove the fuel assemblies from the pool, a critical step in a long decommissioning process that has already had serious setbacks. Just 36 men will carry out the tense operation [...] A separate team will work overnight to clear any debris inside the pool that might cause the fuel to jam when a crane tries to lift it out, possibly causing damage. [...] the work will be carried out by a Tepco-led team and without external supervision. [...]

Underwater cameras will help engineers search for debris, left from the original explosion, that might jam the assemblies, and a robotic arm will be used to try to remove any debris that does get in the way. The crane is designed to hold its load if power is lost, and Tepco said it has doubled the cabling that will lift the cask, which could weigh as much as 90 tons when filled. The biggest fear is that an earthquake or tsunami will disrupt the fuel assembly transfer. [...]

The Risks
[...] The attempt to remove the fuel rods underscores the complicated, potentially hazardous work that lies ahead at the plant [...] it is still dangerous to have the fuel high up in a damaged structure that could collapse in another quake, experts warn. [...] An accident could expose the rods and — in a worst-case

scenario, some experts say — allow them to release radioactive materials beyond the plant. [...] some experts [are] wondering whether the company is up to the task. [...] The worst-case scenario of a breach in the pool, leaving the fuel rods uncovered, has not happened [...]
Shunichi Tanaka, the head of Japan’s Nuclear Regulation Authority: “There are potentially very big risks involved”
Yasuro Kawai, former nuclear plant engineer who now heads a group that is independently monitoring the decommissioning process: “All I can do is pray that nothing goes wrong” [...] He said much depends on whether the assemblies were damaged during removal — for example, if the casks carrying them were to accidentally fall to the ground, exposing the rods — and whether such damage was severe enough to force workers to evacuate. “If they drop the rods, will the situation be easily contained, or do we need to worry about a more dangerous chain of events? There are just too many variables involved to say for sure.”
Lake H. Barrett, special adviser to the president of Tepco and former U.S. Department of Energy official: When the job is done, [he] said, the overall danger will be reduced. This fuel “really needs to come back down to a ground-level pool that is not damaged. That’s going to improve the risk situation.”
France 24, Nov. 11, 2013 — Misa Redwolf, Metropolitan Coalition against Nuclear Power (at 5:30 in): “What if they drop this spent fuel? It wold release massive amounts of radiation. This is an unprecedented operation, so it’s hard to imagine what could happen. I think they should at least evacuate nearby residents before hand.”

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