Kansai outlines plans for dismantling Ohi units

22 November 2018

Kansai Electric Power Company has submitted a detailed decommissioning plan to the Nuclear Regulation Authority (NRA) for units 1 and 2 at its Ohi nuclear power plant in Japan's Fukui Prefecture.

Ohi units 1 and 2 (Image: Kansai)

The utility announced last December that it had decided not to seek permission to restart the two 1175 MWe pressurised water reactors. At that time, it informed Ohi town and Fukui Prefecture of its decision to decommission the units, which began operating in March 1979 and December 1979, respectively. Kansai submitted an application to Japan's Ministry of Economy, Trade and Industry in March formally seeking approval to decommission the units.

Ohi 1 and 2 - which have been offline since July 2011 and December 2011, respectively - are the only reactors in Japan to feature ice condenser emergency cooling systems. These systems employ blocks of ice in a basket installed around the containment vessel to rapidly cool steam generated to reduce pressure in the event of an accident. Kansai said that to comply with new safety standards, the walls of the containment buildings of Ohi 1 and 2 would have had to be widened. Kansai estimated it would have cost some JPY830 billion (USD7.3 billion) to make safety upgrades to the units to meet the required standards.

Kansai today announced that it has submitted a detailed decommissioning plan to the NRA outlining the facilities and equipment to be dismantled and a timetable for completing the work.

According to the plan, decommissioning of Ohi 1 and 2 will take about 30 years and will be carried out in four stages. The first stage, lasting about eight years, will involve preparing the reactor for dismantling (including the removal of all fuel and surveying radioactive contamination), while the second, lasting ten years, will be to dismantle peripheral equipment from the reactor and other major equipment. The third stage, taking about six years, will involve the demolition of the reactor itself, while the fourth stage, taking about three years, will see the demolition of all remaining buildings and the release of land for other uses.

During the first stage, all fuel is to be removed from the units. This includes 76 unused fuel assemblies and 323 used assemblies from unit 1 and 140 unused assemblies and 306 used assemblies from unit 2.

A total of 400 tonnes of high-level radioactive waste is expected to result from the decommissioning of Ohi 1 and 2, together with 2850 tonnes of low-level waste and 20,240 tonnes of very low-level waste. A further 13,200 tonnes of non-radioactive waste will also be generated through the clearance of the site.

In mid-March 2015, the Ministry of Economy, Trade and Industry's Agency for Natural Resources and Energy revised the accounting provisions in the Electricity Business Act, whereby electric power companies can now calculate decommissioning costs in instalments of up to ten years, instead of one-time as previously. This enhanced cost recovery provision was to encourage the decommissioning of older and smaller units.

So far, nine operable Japanese reactor have been declared for decommissioning since the Fukushima Daiichi accident in 2011.

Researched and written by World Nuclear News