Modification of the STACY Critical Facility for Experimental Study on Fuel Debris Criticality Control

Abstract

For the decommissioning of the Fukushima Daiichi Nuclear Power Stations, fuel debris involving molten structural materials should be retrieved from each reactor unit. The fuel debris, which is of uncertain chemical composition and physical state, needs to be treated with great care from the standpoint of criticality safety. For developing criticality control for the fuel debris, the Japan Atomic Energy Agency (JAEA) has been planning to modify the Static Experiment Critical Facility (STACY) and to pursue critical experiments on fuel debris. STACY, a facility using solution fuel, is to be converted into a thermal critical assembly using fuel rods and a light water moderator. A series of critical experiments will be conducted at the modified STACY using simulated fuel debris samples. The simulated fuel debris samples are to be manufactured by mixing uranium oxide and reactor structural materials with various chemical compositions. This report summarizes a facility development project for an experimental study on criticality control for fuel debris using the modified STACY and simulated fuel debris samples.

Criticality Characteristics and Sensitivity Analysis of Fukushima Debris Beds Containing MCCI Products

“…Only few quantitative results have been published until now [6][7][8]. The critical experiments will be conducted with the Static Experiment Critical Facility (STACY) whose core is currently being modified [9,10]. Meanwhile, the situation inside the damaged reactors is being surveyed in order to gather new information that will enable a more realistic estimation of the criticality risks.…”