TEPCO has published a digest of a three-phase plan to decommission Fukushima Daiichi units 1-4, which is expected to take 40 years.
Diagram of the final stage of decontamination: fuel debris removal. Starting these operations relies on lots of preparatory work, including decommissioning reactor building interiors, sealing leaks in lower and upper parts of PCV, multiple investigation and sampling missions, R&D, filling PCV with water, constructing new reactor building cover and removing RPV head.
Phase one ends with the start of removal of fuel from the spent fuel pools (beginning with unit 4), and is targeted to end in two years (that is, by the end of 2013). In this operation, a fuel handling machine mounted above the pool would place spent fuel into containers under water, and then the reactor’s overhead crane would lower the containers to ground level. Other tasks in phase one include maintaining on-site dose below 1 mSv/yr, maintain stable reactor cooling and accumulated water processing, starting fuel debris removal R&D and decontamination and starting radwaste processing and disposal R&D.
Phase two ends with the start of removal of fuel debris—solidified material from melted fuel, and is targeted to end in 10 years (that is, by the end of 2021). Other tasks in phase two include completion of spent fuel removal (unit 3 would be the second pool emptied), perform preparations for fuel debris removal, including decontaminating reactor building interiors, fixing PCV leaks and flooding PCVs, continuing stable reactor cooling, completing processing of accumulated water, continuing fuel debris removal R&D, and starting R&D on reactor facility decommissioning. The detailed plan to remove fuel debris consists of these steps: investigation of PCV leaks in early 2015; verify PCV repair technology on-site in early 2016; flood bottom of PCV; verify PCV inspection technology on-site in early 2017; investigate; repair upper parts of PCVs, and then flood them with water; after installing building cover, open RPV head; verify RPV internal inspection technology by mid-2019; investigate; develop removal methodology; develop debris container; establish method to weigh fuel debris; begin removal.
Phase three ends with total decommissioning of the site, in 30-40 years (by 2041-2051). Other tasks in phase three include completing fuel debris removal (in 20-25 years, that is by 2031-2036), and implementing radioactive waste processing and disposal.
For now, however, the document says that TEPCO is working to a three-year plan from a safety directive produced by the government regulator Nuclear and Industrial Safety Agency called ‘Ensuring mid-term safety’. Targets and schedules will be released on an annual basis.
The document says that TEPCO’s on-site project structure, which includes the input of 400 subcontractors, will continue, although it will work with outside agencies for R&D.
The mid-to-long-term roadmap also said:
-In 2012, the accumulated water processing equipment will receive new a processing system to remove ‘multi-reactive nuclides’ that cannot be removed with the current caesium decontamination systems.
-By 2014, water shielding walls will be built around the Fukushima Daiichi harbour to protect the sea from radioactive nuclide leaks. Inside the plant’s breakwater, the seafloor will either be dredged or covered, depending on the location, to further reduce the risk of leaks.
-By 2013, the team will develop a plan to establish R&D for post-accident waste.
The mid and long-term roadmap report was drafted by TEPCO and Japanese government agencies Nuclear and Industrial Safety Agency and the Ministry of Education, Trade and Industry’s Agency for Natural Resources and Energy (ANRE).
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