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Decommissioning Fukushima not quite so obvious

March 4, 2014

Technology and working conditions for decommissioning process still lacking





Fukushima No. 1 Nuclear Power Plant (above) on March 12, 2011, the day after it was struck by a massive earthquake and tsunami, and the same plant on Feb. 17, 2014. (Mainichi)



Workers at the Fukushima No. 1 Nuclear Power Plant began removing spent nuclear fuel rods from the No. 4 reactor's cooling pool in November 2013. But spent fuel in reactors No. 1, 2 and 3 has remained untouched, and we still lack technology that can withstand high levels of radiation in the decommissioning process. Considering this is a major undertaking that will take up to 40 years, we have barely taken the first step.

A decommissioning roadmap compiled by the government and Fukushima plant operator Tokyo Electric Power Co. (TEPCO) defines the period until removal of spent fuel rods is begun as period 1; the period until the removal of molten fuel in reactors No. 1-3 as period 2; and the period in which molten fuel removal is completed and the reactor buildings are dismantled as period 3.

Of the 1,533 spent fuel rods that were in the cooling pool of the No. 4 reactor, about one-fourth or 418 rods had been extracted as of March 3. The majority of the fuel rods have remained intact, and TEPCO plans to remove all of them before the end of the year.

The biggest hurdle TEPCO faces is the removal of molten fuel in the No. 1-3 reactors. Effects of the March 11, 2011 tsunami left the three reactors without their cooling capacity, and temperatures in the reactor containment vessels rose at one point to at least 2,000 degrees Celsius. The majority of the reactors' 1,496 fuel rods are believed to have melted.

To remove the fuel, the containment vessels must be filled with water to block radiation. To do so, however, it is essential that working conditions are improved, damage to the vessels is identified and repaired, and more advanced technologies are developed.

If all goes smoothly, fuel extraction will begin in the No. 1 and 2 reactors in fiscal 2020, and in the No. 3 reactor in fiscal 2021. With the Summer Olympics set to be held in Tokyo in 2020, it will be up to the government to prove both domestically and internationally that we are headed toward decommissioning. There are a total 1,573 spent fuel rods in the three reactors' cooling pools, and removal will begin in fiscal 2015 for the No. 3 reactor, and in fiscal 2017 for the No. 1 and 2 reactors at the earliest.

Meanwhile, TEPCO decommissioned the No. 5 and No. 6 reactors on Jan. 31 this year at the behest of the government. The two reactors will hereafter be used as model reactors for decommissioning the No. 1, 2, 3 and 4 reactors. According to Japan Atomic Industrial Forum President Takuya Hattori, the No. 5 reactor is the same type of reactor as the No. 1-4 reactors, and using it for practice could help cut back on the time it takes to decommission the others.

However, it is unclear whether the quantity and quality necessary for upcoming work at the nuclear plant can be maintained. TEPCO calculates that radiation exposure levels among workers by the time spent fuel extraction from the No. 4 reactor's cooling pool is completed will be a maximum 32 millisieverts per person. While the figure falls below the maximum permitted figure of 50 millisieverts per year and 100 millisieverts within a five-year period, radiation levels at reactors No. 1-3 is high, and the success of the decommissioning process relies heavily on whether TEPCO can continue to secure technical staff and other workers.

"From the standpoint of the entire decommissioning process, we are now standing at the foot of the mountain range, where we cannot see the mountaintop. There are going to be steep slopes and drop-offs waiting up ahead, such as the removal of molten fuel," says Nagoya University professor Akio Yamamoto, who was involved in the creation of Japan's new nuclear safety standards. "Those on the ground face excessive burdens, including dealing with contaminated water. We urgently need to improve compensation for workers."

March 04, 2014(Mainichi Japan)


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