Modification and resumption of the Static Experiment Critical Facility (STACY)

Ishii, Junichi; Seki, Masakazu; Aizawa, Eiju; Sumiya, Masato; Maekawa, Tomoyuki; Arakaki, Yu; Hasegawa, Kenta; Araki, Shohei   ; Izawa, Kazuhiko ; Gunji, Satoshi  

The removal of fuel debris is one of the most important and challenging tasks in the decommissioning of power reactors damaged in the 2011 accident at Fukushima Daiichi Nuclear Power Plant (1F). The Japan Atomic Energy Agency (JAEA) has implemented a renewal program of the Static Experiment Critical Facility (STACY), transitioning it from a homogeneous solution system to a heterogeneous water-moderated system, in order to verify the criticality calculations that consider the fuel debris from the 1F accident. The first criticality of the modified STACY was achieved in April 2024. After a series of performance inspections, an experimental campaign for the investigation of fuel debris characteristics was started in August 2024. In this paper, we describe the main equipment of the modified STACY. In addition, the experimental equipment for the debris-simulated core configuration is also introduced.