Fukushima Daiichi decontamination and decommissioning: current status and challenges.

Abstract

It has been nearly 10 years since the accident at Fukushima Daiichi nuclear power plant. With the cooperation of those involved, the site, which was once in a crisis situation, has improved to the point where it is possible to look ahead and proceed with work on schedule. In the off-site area, conditions for returning home have been progressed, and evacuation orders for some areas have been lifted by the Japanese Government. This article describes, in respect of the various efforts being made on site at the moment, the current status of fuel removal from the spent fuel pools, preparations for fuel debris retrieval, improvement of the working environment, and future plans. Removal of fuel from the spent fuel pool for Unit 4 was completed in December 2014, and work is continuing with Unit 3 in order to complete by March 2021. The decision was made to install a large cover in advance for Unit 1 in consideration of the risk of dust scattering, and to conduct fuel removal for Unit 2 from the south side without dismantling the existing upper section of the building. The target is for fuel removal from the pools, including Units 5 and 6, to be complete by 2031. Regarding fuel debris retrieval, progress in various investigations has made it possible to grasp the distribution of debris in the reactor containment vessels of Units 1-3 to a certain extent, and it was decided that the first retrieval will start with the most-investigated unit (Unit 2). A robot arm will be used for retrieval; initially, a trial retrieval will be started, and once the retrieval method has been verified and confirmed, the scale of retrieval will be expanded in stages using a device with the same mechanism. The working environment of Fukushima Daiichi nuclear power plant has also improved. By reducing the stirring up of radioactive materials due to facing (paving), etc., it became possible to reduce the degree of protective clothing needed, and the area in which people can work with simple clothing such as general work clothes now represents 96% of the entire site. Due to various reduction measures, the effective dose of workers is currently approximately 0.2-0.4 mSv month-1 on average per person. The work environment will continue to be improved steadily in the future. Finally, I would like to briefly mention the direction of future decommissioning efforts. The decommissioning of Fukushima Daiichi nuclear power plant and contaminated water management are being implemented based on the national Mid-and-Long-Term Roadmap. The latest edition (5th revision) sets out the milestones until 2031, and we are on target to achieve the goals set forth here and the goals set forth in the Nuclear Regulatory Commission's risk map. To that end, the Mid-and-Long-Term Decommissioning Action Plan 2020, which shows the main work processes of the decommissioning, was announced. This will enable us to proceed with decommissioning work more systematically in the future while looking ahead. Local people who sometime are concerned about risk arising from Fukushima Daiichi may grasp the future work plan concretely in relief, and can consider taking part in the decommissioning work. The key lies in how we can contribute to the reconstruction of Fukushima through the decommissioning of Fukushima Daiichi nuclear power plant, and we will continue to take responsibility for decommissioning of the power plant and contaminated water management under the principle of 'striking a balance of reconstruction and decommissioning'.