The government and Tokyo Electric Power Co. (TEPCO) are set to extract a small sample of melted nuclear fuel from the bottom of the No. 2 reactor's containment vessel at the disaster-stricken Fukushima No. 1 nuclear plant as early as fiscal 2019.
The operation will be a test before starting full-scale collection of the fuel, targeted for 2021 or earlier. If development of technologies for debris retrieval shows promise, the operation may be moved up to the end of fiscal 2018. The government and TEPCO hope to ascertain the properties of the melted fuel and use the information for developing collection devices and debris containers.
This will be the first attempt to sample nuclear fuel debris from a reactor. Other materials, including those floating in contaminated water and substances stuck to robot probes, have been extracted from the plant's reactors before. The No. 1, 2 and 3 reactors at the Fukushima No. 1 plant melted down in the March 2011 nuclear disaster.
The road map for collecting the melted fuel, last revised in September 2017, states that TEPCO would choose a first reactor to tackle by the end of fiscal 2019 and decide on a collection method. The utility would then start the retrieval process in 2021. As deciding on this process requires finalizing ways to contain, transfer and store the debris, the government and utility concluded that they would need to grasp the fuel's current condition by extracting samples beforehand.
In January this year, a camera and dosimeter were sent into the containment vessel of the No. 2 reactor through an existing passage to find pebble- and clay-like masses at its bottom believed to be melted fuel. A source close to the government says the plan is to remotely guide a robot arm equipped with a camera and dosimeter into the containment vessel through the same passage, and extract a small amount of the suspected fuel debris.
The January probe of the containment vessel revealed radiation around the pebble-like masses measured 8 sieverts per hour -- a level potentially lethal to humans after just one hour of exposure. Due to the ultrahigh radiation, the sampled material will be placed in a special radiation-shielded container before being removed from the reactor. After that, the sample will be brought to a Japan Atomic Energy Agency facility in Ibaraki Prefecture for analysis.
A government source told the Mainichi Shimbun that sampling the suspected fuel debris is different from the debris collection specified in the road map, and stressed that extracting samples should be beneficial to determine a method for retrieving the fuel.