Japan’s Tohoku Electric Power Company has filed an application with the Nuclear Regulation Authority (NRA) for approval of its decommissioning plan Onagawa 1 in Miyagi Prefecture.
Tohoku has requested preliminary talks with local authorities in Miyagi Prefecture, Onagawa Town and Ishinomaki City.
Tohoku Electric confirmed in October 2018 that it would decommission the 524MWe boiling water reactor (BWR), citing difficulties in implementing the additional safety measures needed following the 2011 Fukushima-Daiichi accident.
Tohoku said restricted space within Onagawa's containment vessel made it difficult to install safety equipment, such as fire extinguishing equipment, power supply equipment and alternative water injection pumps. The relatively small output of the unit made it unprofitable.
Onagawa 1 began commercial operation in June 1984 and is the oldest of four units owned and operated by Tohoku Electric – Onagawa 2 and 3 (both larger 825MWe BWRs, which began operating in 1995 and 2002) and Higashidori, in Aomori Prefecture, which started operation in late 2005.
The basement floors of Onagawa 2 were flooded following the March 2011 earthquake and tsunami and Tohoku Electric is building a 30-metre-high sea wall to comply with the new post-Fukushima stricter safety requirements. Tohoku Electric plans to restart Onagawa 2 in fiscal 2020 at the earliest, provided it meets current safety standards. Tohoku Electric filed a restart application for Onagawa 2 in December 2013 and for Higashidori 1 in June 2014.
Onagawa 1 was the tenth operable Japanese reactor to be declared for decommissioning since the Fukushima Daiichi accident. Tohoku’s decommissioning plan for the unit outlines the facilities and equipment to be dismantled and a timetable for completing the work.
Decommissioning will take about 34 years and will be carried out in four stages.
During the first stage, 821 used fuel assemblies stored in Onagawa 1's storage pool, will be transferred to the storage pool for Onagawa 3. These assemblies will eventually be transported for reprocessing.
Some 60 tonnes of high-level radioactive waste is expected to be generated through the decommissioning of Onagawa 1, together with 740 tonnes of low-level waste and 5340 tonnes of very low-level waste. A further 12,400 tonnes of non-radioactive waste will also be generated through the clearance of the site.
Tohoku said it expects the decommissioning of Onagawa 1 to cost a total of JPY41.9 billion ($392 million), with dismantling activities costing JPY30.0 billion and waste disposal accounting for the remainder.
Photo: Onagawa Nuclear Power Plan taken by Nekosuki600(talk / Contributions) in November 16th 2003 and uploaded by Nekosuki600(talk / Contributions) to Japanese Wikipedia in September 25th 2005