Criticality safety control of fuel debris produced by the accident of Fukushima Daiichi nuclear power plants - technical development in Japan from 2012 and the future

Full text of publication follows: On 11 March 2011, Japan was attacked by the '2011 off the Pacific coast of Tohoku Earthquake'. It was the greatest earthquake ever recorded around Japan. It caused big tsunami and it also attacked Tohoku sea coast area severely and violently. Approximately 16,000 people passed away and still about 2,600 people are lost by the earthquake and the tsunami. This extraordinary natural disaster affected the society of Japan deeply. But more serious problem is the severe accident occurred in Fukushima Daiichi Nuclear Power Plants (1FNPP) after the earthquake and tsunami attack. By the tsunami after the earthquake, because of loss of ultimate heat sink (LUHS), three reactors of 1FNPP were damaged and the intact fuel became fuel debris. After the accident, Government of Japan setup the council for the decommissioning of TEPCO's Fukushima Daiichi Nuclear Power Plant and it released the general plan for countermeasure of the severe accident occurred in Japan, i.e. 'Mid-and-long-Term Road map towards the Decommissioning of Fukushima Daiichi Nuclear Power Units 1-4'. According to the road map, nuclear power reactor vendors and research institutes in Japan have started the national project to carry out the decommissioning activity. International Research Institute for Nuclear Decommissioning (IRID) is the association for technical development for Fukushima site decommissioning. Under this umbrella, nuclear power reactor vendors in Japan, i.e. Toshiba, Hitachi and Mitsubishi, and Japan Atomic Energy Agency (JAEA) have carried out the technical development required for the criticality safety control of the Fukushima fuel debris. Furthermore, JAEA has a plan to use the criticality assembly STACY for obtaining the neutronics characteristics of the fuel debris by modifying STACY from the solution system to heterogeneous system. This program is conducted by entrustment of Nuclear Regulation Authority of Japan, independently from IRID framework. It is expected that it will reach first criticality in FY2018. Researchers in universities in Japan also have own research program to control reactivity of fuel debris. This presentation will summarize the on-going research programs in Japan for the criticality safety control in order to remove and store the fuel debris from Fukushima site. (author)