Kimimasa Mayama, Associated Press
TOKYO — It's costly, risky and dependent on technologies that have yet to be fully developed. A decades-long journey filled with unknowns lies ahead for Japan, which took a small step this week toward decommissioning its crippled Fukushima nuclear power plant.
Nobody knows exactly how much fuel melted after the March 2011 earthquake and tsunami knocked out cooling systems. Or where exactly the fuel went — how deep and in what form it is, somewhere at the bottom of reactor Units 1, 2 and 3.
The complexity and magnitude of decommissioning the Fukushima Dai-ichi plant is more challenging than Three Mile Island or Chernobyl, say experts such as Lake Barrett, a former U.S. regulator who directed the Three Mile Island cleanup and now is an outside adviser to Fukushima operator Tokyo Electric Power Co.
One core melted at Three Mile Island in 1979, versus three at Fukushima, and it didn't leak out of the containment chamber, the outer vessel that houses the reactor core. At Fukushima, multiple hydrogen explosions caused extensive damage, blowing the roofs off three reactor buildings and spewing radiation over a wide area.
Chernobyl was a worse accident in terms of radiation emitted, but authorities chose an easier solution: entombing the facility in cement.
At Fukushima, TEPCO plans a multi-step process that is expected to take 40 years: Painstakingly removing the fuel rods in storage pools, finding and extracting the melted fuel within the broken reactors, demolishing the buildings and decontaminating the soil.
"This is a much more challenging job," Barrett said during a recent visit to Japan. "Much more complex, more difficult to do."
Also, water must continuously be channeled into the pools and reactor cores to keep the fuel cool. Tons of contaminated water leaks out of the reactors into their basements, some of it into the ground.
Uncertainty runs high as Japan has never decommissioned a full-size commercial reactor, even one that hasn't had an accident. TEPCO has earmarked about 1 trillion yen ($10 billion) for the decommissioning, and says it will agree to Prime Minister Shinzo Abe's request to set aside another 1 trillion yen to fight water leaks.
The government itself has contributed or promised 145 billion yen, and is expected to step up its involvement in the years to come, following criticism over its lack of support and growing concern that the technical and funding challenges are beyond TEPCO's capabilities.
TEPCO began removing fuel rods Monday from a storage pool at Unit 4, whose building was severely damaged but didn't have a meltdown because the fuel had been removed from the core for maintenance. In an underwater operation, 22 of the 1,533 sets of fuel rods in a pool on the building's top floor were transferred to a cask that will be used to move them to safer storage. By 2018, the utility hopes to remove all 3,100 fuel assemblies from storage pools at the four damaged units.
After that would come the real challenge: removing melted or partially melted fuel from the three reactors that had meltdowns, and figuring out how to treat and store it so it won't heat up and start a nuclear reaction again.
"This is an unprecedented task that nobody in the world has achieved. We still face challenges that must be overcome," said Hajimu Yamana, a Kyoto University nuclear engineer who heads a government-affiliated agency that is overseeing technological research and development for the cleanup.
Closing the holes and cracks in the containment vessels is the biggest hurdle in the decommissioning process, experts say. Every opening must be found and sealed to establish a closed cooling system. Then, under the current plan, the next step would be to fill the reactor vessels with water and examine the melted fuel.
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