Mitsubishi Heavy Industries (MHI) said it recently started manufacturing casks for the transport and storage of used nuclear fuel for Shikoku Electric Power Company. The utility will use them at an interim dry storage facility at its Ikata nuclear power plant in Japan's Ehime Prefecture.

A dry transport and storage cask for used nuclear fuel (Image: MHI)

Shikoku plans to build and start operation of a dry storage facility at the Ikata plant by February 2025. The company began constructing the facility - which will store used fuel from the plant until it can be transported to the reprocessing facility in Rokkasho Village, Aomori Prefecture - in November last year.

The new facility - measuring about 60 metres in length, 40 metres wide and with a height of 20 metres - will have the capacity to store about 1200 fuel assemblies, contained within 45 dry casks.

MHI said it has started manufacturing at its Kobe Shipyard plant the first of 15 casks to be delivered to the storage facility once its construction has been completed. Fourteen of these casks will be used to store used fuel from units 1 and 2 of the Ikata plant, while the other one will hold fuel from unit 3.

Each cask - with a height of 5.2 metres and a diameter of 2.6 metres - will weigh about 120 tons once filled with fuel assemblies.

Ikata 3 is one of the few Japanese reactors to have been restarted since the March 2011 accident at the Fukushima Daiichi plant. The 846 MWe (net) pressurised water reactor (PWR) received approval from the Nuclear Regulatory Authority to resume operation in April 2016, having been idle since it was taken offline for a periodic inspection in April 2011. Shikoku declared the unit back in commercial operation on 7 September 2016.

Shikoku decided to decommission Ikata units 1 and 2 - both 538 MWe (net) PWRs - in March 2016 and March 2018, respectively.

MHI noted that demand for interim on-site storage of used fuel at Japanese nuclear power plants is increasing. The temporary storage - up to 60 years - of fuel allows it to cool over time prior to it being recycled.

"The dry cask, which forms the core of dry storage, is a dedicated container that can be used for both transportation and storage," it said. "After storing spent fuel on the premises of a power plant for a certain period of time, it can be taken out of the power plant without needed to be transferred into other transportation containers. It has high robustness and versatility."

MHI said it has "established a mass production supply system for high-quality casks with short delivery times and excellent economic efficiency by establishing a dedicated cask assembly factory with highly automated manufacturing and inspection while making use of our know-how in manufacturing nuclear equipment."

Researched and written by World Nuclear News