Chapter 22
Modification of the STACY Critical Facility
for Experimental Study on Fuel Debris
Criticality Control
Hiroki Sono, Kotaro Tonoike, Kazuhiko Izawa, Takashi Kida,
Fuyumi Kobayashi, Masato Sumiya, Hiroyuki Fukaya, Miki Umeda,
Kazuhiko Ogawa, and Yoshinori Miyoshi
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.
Keywords Critical facility • Criticality control • Criticality safety • Fuel debris
• Fukushima Daiichi • Simulated fuel debris sample • STACY
22.1 Introduction
In the severe accident at the Fukushima Daiichi Nuclear Power Stations (NPS),
most of the fuel loaded in the cores of Units 1, 2, and 3 was seriously damaged and
melted, resulting in a considerable amount of fuel debris [1]. It is believed that some
parts of the fuel debris involve molten structural materials such as zircaloy,
stainless steel, and concrete. This fuel debris, which contains much burned fuel,
H. Sono (*) • K. Tonoike • K. Izawa • T. Kida • F. Kobayashi • M. Sumiya
H. Fukaya • M. Umeda • K. Ogawa • Y. Miyoshi
Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki, 319-1195, Japan
e-mail: sono.hiroki@jaea.go.jp
© The Author(s) 2015
K. Nakajima (ed.), Nuclear Back-end and Transmutation Technology for Waste
Disposal, DOI 10.1007/978-4-431-55111-9_22
261
Modification of the STACY Critical Facility
for Experimental Study on Fuel Debris
Criticality Control
Hiroki Sono, Kotaro Tonoike, Kazuhiko Izawa, Takashi Kida,
Fuyumi Kobayashi, Masato Sumiya, Hiroyuki Fukaya, Miki Umeda,
Kazuhiko Ogawa, and Yoshinori Miyoshi
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.
Keywords Critical facility • Criticality control • Criticality safety • Fuel debris
• Fukushima Daiichi • Simulated fuel debris sample • STACY
22.1 Introduction
In the severe accident at the Fukushima Daiichi Nuclear Power Stations (NPS),
most of the fuel loaded in the cores of Units 1, 2, and 3 was seriously damaged and
melted, resulting in a considerable amount of fuel debris [1]. It is believed that some
parts of the fuel debris involve molten structural materials such as zircaloy,
stainless steel, and concrete. This fuel debris, which contains much burned fuel,
H. Sono (*) • K. Tonoike • K. Izawa • T. Kida • F. Kobayashi • M. Sumiya
H. Fukaya • M. Umeda • K. Ogawa • Y. Miyoshi
Japan Atomic Energy Agency, Tokai-mura, Naka-gun, Ibaraki, 319-1195, Japan
e-mail: sono.hiroki@jaea.go.jp
© The Author(s) 2015
K. Nakajima (ed.), Nuclear Back-end and Transmutation Technology for Waste
Disposal, DOI 10.1007/978-4-431-55111-9_22
261