Chubu Electric Power Co has begun dismantling the reactor at unit 2 of its Hamaoka NPP in Omaezaki, Shizuoka Prefecture – Japan’s first commercial reactor to undergo the process.
Disassembly work started with removal of the top lid of the pressure vessel. The lid, with a diameter of about 6 metres, about 3 metres in height and about 80 centimetres thick, was removed by a crane. According to Chubu Electric, the first step involves cutting the lid into smaller sections approximately 4 metres long and 1 metre wide. This is set to begin on 27 March, 2025. Removal of the lid is expected to be completed by July 2025.
Dismantling of the reactor takes place in the third of the four phases in decommissioning nuclear installations. In December, the Nuclear Regulation Authority gave approval to Chubu Electric to begin this phase for the reactors at Hamaoka units 1&2. Chubu Electric first began preparation for dismantling the reactor at unit 2 while it secured a site to temporarily store its radioactive waste before beginning work on unit 1.
Units 1&2 are boiling water reactors. Unit 1 (540 MWe) began operating in 1976 and unit 2 (840 MWe) in 1978. Due to updated seismic regulations introduced after the 2006 earthquake, Chubu Electric decided in 2008 to decommission both units. Initial work began in 2009. Used fuel from the reactors has been transferred to the used fuel pools of units 4&5 on the same site and all fresh fuel has been removed from removed. The facility has undergone extensive decontamination work, as well as decommissioning turbines, generators, and some reactor building components since 2015.
Chubu Electric initially planned to begin dismantling the reactors in fiscal 2023, but postponed the start of work for a year to study measures against radiation exposure. In 2024, it then extended the duration of dismantling work from six to 12 years. Chubu Electric plans to begin the fourth decommissioning phase – tearing down the reactor building – in fiscal 2036 and to complete decommissioning work in fiscal 2042.
However, decommissioning of the reactors is the most difficult procedure because of the high radiation levels present. To manage the hazardous conditions, specialised robots will be deployed to operate remotely, ensuring the safety of the workers involved during the project.
The entire process is expected to generate around 450,000 tonnes of metal and concrete waste, approximately 20,000 tonnes of which will be classified as low-level radioactive waste. The waste will be structured classified according to contamination levels: L1 (control rods), L2 (parts of the reactor pressure vessel), and L3 (peripheral piping). However, as yet a disposal site for this waste has not been decided, causing concern about the environmental impact.
Chubu Electric estimates that the decommissioning of the unit 1 reactor will cost about JPY37.9bn ($254.4m) and the unit 2 reactor about JPY46.2bn.
