With the accident at the Three Mile Island nuclear plant as a guide, the government and Tokyo Electric Power Co. on Dec. 21 released a road map for decommissioning the stricken No. 1 through No. 4 reactors at TEPCO's Fukushima No. 1 nuclear power plant that will take decades.
The road map envisages removal of the melted fuel debris to be complete in 20-25 years, followed by a dismantling of the buildings to conclude the decommissioning process, which could take "30-40 years."
"We have come forward with a feasible road map and feasible timelines," Yukio Edano, industry minister, told a news conference.
Local government leaders reacted immediately to news of the decommissioning program, which may last up to 40 years.
"It will be an extremely long term, globally unprecedented and difficult effort," said Yuhei Sato, the governor of Fukushima Prefecture. "It will be essential to disclose information in a timely manner to make it clearly known how the work is proceeding and to take thorough safety measures."
The road map divides the entire process into three periods: Phase 1 (within 2 years), which lasts until the removal of spent fuel rods begins; Phase 2 (within 10 years), which lasts until the removal of melted fuel debris begins; and Phase 3 (until 30-40 years from now), leading up to the end of decommissioning. Necessary tasks and challenges were identified for each phase.
For Phases 2 and 3, the road map set a number of "confirmation points" where the decommissioning plan will be reviewed depending on the extent of technological advancements and the situation of the reactor interiors to be revealed by inspection cameras.
The new road map was based on a report, drawn up earlier this month by the Japan Atomic Energy Commission, which studied the decommissioning process at the Three Mile Island nuclear plant in the United States where a core meltdown occurred in 1979.
The envisaged time to start removing fuel rods from the spent fuel storage pools, or two years from now, was moved up one year from what was indicated in the JAEC report.
While the JAEC report said it will take "30 years or more" to end the decommissioning, the road map revised that estimate to "30-40 years from now" to allow for a possible prolonged process.
A new "government and TEPCO council on mid- to long-term measures," co-chaired by Edano and Goshi Hosono, state minister in charge of handling the Fukushima nuclear accident, endorsed the road map following the government's Dec. 16 announcement on the completion of Step 2 in a separate road map toward bringing the crippled nuclear reactors under control.
A senior official of the Fukushima prefectural government appeared cautious.
"High-level radioactive waste will keep piling up while the decommissioning work goes on," the official said. "We will have to keep talking to the central government over the long term so that Fukushima Prefecture will not end up turning into a final disposal field."
"Nobody has ever experienced any effort like that," said Toshitsuna Watanabe, the mayor of Okuma, home to the No. 1 through No. 4 reactors of the Fukushima No. 1 nuclear plant. "The schedule may have accounted for some safety leeway."
Katsutaka Idogawa, the mayor of Futaba, which hosts the No. 5 and No. 6 reactors of the same plant, also expressed concerns.
"There will be a lot of things that technologies and protocols, envisaged before the accident, will not be sufficient to deal with," he said.
That view was shared by Hosono as well.
"We have to prepare for a lot of obstacles along the road to decommissioning," the industry minister said Dec. 21 during a speech to kick off the meeting that approved the new road map.
While it took slightly over 10 years, following the Three Mile Island accident, to finish the removal of fuel, more than double that duration was seen for the same process at the Fukushima No. 1 nuclear plant.
At the Three Mile Island plant, a core meltdown occurred at only one reactor, where the fuel stayed inside the pressure vessel. During the Fukushima accident, core meltdowns occurred in three reactors and fuel fell through to the containment vessels, which forebodes enormous difficulties in the removal and repair work.
PHASE 1: REMOVAL OF SPENT FUEL RODS
Concrete tasks were specified for Phase 1, which will run through the end of 2013. Most of the tasks described are ones that could commence immediately.
The removal of spent fuel rods from the storage pools will be started, from the No. 4 reactor first, by the end of 2013. This will concur with preparations for the eventual removal of melted fuel debris--the central task in the decommissioning process--including research and decontamination of the building interiors.
During Phase 1, reactors will continue to be cooled by pumping in radioactive water treated with the "cyclic water injection and cooling system" that is currently in operation.
At present, water is being pumped through hoses and pipes that have a total combined length of 4 kilometers, but they will be shortened to about half that next year to enhance safety. However, the temporary facilities, where water leaks have occurred repeatedly, will continue to be used.
By way of preventing the spread of seawater contamination, seabed soil near the water intakes of the nuclear plant will be covered with concrete or other material by autumn 2012 to block the dispersion of radioactive substances.
The fuel to be removed from the spent fuel storage pools will be moved to a "storage pool for common use" beside the No. 4 reactor, where damage from the Great East Japan Earthquake, which triggered the nuclear accident, was relatively mild. To prepare for that displacement, the common-use storage pool will be inspected and restored by some time around the end of 2012.
The road map also contains a simulation of the workforce that will be required for the decommissioning work for the foreseeable future. The first year will require 11,700 workers if the annual radiation dose limit is set at 20 millisieverts, but there will be no shortage of a workforce, the document said.
PHASE 2: FILLING CONTAINMENT VESSELS WITH WATER
The decommissioning work will gain full steam during Phase 2. Shielding work will be done to prevent the leakage of radioactive water from reactor buildings into turbine buildings. A stable cooling system will be installed after all radioactive water has been removed from the buildings.
A key point in the process will be the filling of containment vessels with water. Removal of fuel from there will require that the surroundings be filled with water, both to shield radiation and to cool the fuel.
Determining the extent of damage to the containment vessels and deciding what method should be used to repair them will constitute an important "confirmation point."
The containment vessels will be repaired around 2016, followed by investigations of the containment vessel interiors around 2017 and of the pressure vessel interiors around 2019. The target date for starting the removal of melted fuel debris is by the end of 2021.
The repairs and investigations, however, will have to be conducted remotely. If the tasks take more time than expected or have to be abandoned, that will seriously affect subsequent work schedules.
PHASE 3: REMOVAL OF MELTED FUEL DEBRIS
The removal of melted fuel debris, assigned to Phase 3, will take 10-15 years. Completion of that stage will mean that the reactors are finally under safe control.
The goal is to dismantle the buildings and to decide on the method of fuel disposal by the time the road map is completed 30-40 years from now.
But many issues remain unanswered, including what the stricken nuclear plant site will look like when the process is over. Whether the grounds will be turned into a vacant lot or will still contain facilities to store the removed fuel "so far remains in limbo," said an official at the Agency for Natural Resources and Energy.
No estimate was given of the costs of the long-term decommission process. The road map also failed to address what to do with the No. 5 and No. 6 reactors.
(This article was written by Eisuke Sasaki and Tatsuyuki Kobori.)
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