International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators

4-8 May 2009, Vienna
ADS/ET-03

Subcriticality Measurements in Accelerator-Driven System at Kyoto University Critical Assembly

C.H. Pyeon, T. Misawa, J.Y. Lim and S. Shiroya

Kyoto University, Osaka, Japan

Corresponding Author: pyeon@rri.kyoto-u.ac.jp

Subcriticality measurements in the Accelerator-Driven System (ADS) at the Kyoto University Critical Assembly (KUCA) are described in this paper. The Kyoto University Research Reactor Institute is going ahead with an innovative research project on ADS using a Fixed Field Alternating Gradient (FFAG) accelerator. The goal of the research project is to demonstrate the basic feasibility of ADS as a next-generation neutron source using KUCA coupled with a newly developed variable energy FFAG accelerator. The construction of the accelerator complex has been completed and its beam commissioning is currently being conducted. It is expected that the ADS experiments using the FFAG accelerator could start in February 2009. At the ADS with the FFAG accelerator, the high-energy neutrons generated by nuclear reactions with 150 MeV proton beams in a tungsten target will be injected into a solid-moderated and reflected core (A-core) in thermal neutron field of KUCA. The maximum power of the A-core and maximum neutron yield at the target are limited to 100 W and 1x1010 n/s, respectively, and the average beam current is 1 nA. Prior to the ADS experiments with 150 MeV protons, the ADS experiments with 14 MeV neutrons, which is a conventional pulsed neutron generator of the Cockcroft-Walton type accelerator, have been conducted in KUCA, including subcriticality, neutron multiplication, reaction rate distribution, neutron spectrum, neutron decay constant. Among these reactor physics parameters, an exact measurement of subcriticality is an interesting issue in the ADS studies. At the KUCA A-core, subcriticality measurement experiments the ADS with 14 MeV neutrons are carried out by using several methods: Feynman-alpha, Rossi-alpha, Neutron source multiplication and Pulsed neutron methods. In these subcriticality benchmark problems, these facts are demonstrated experimentally that the dependence of subcriticality on the detector positions is found, and that the measurement precision varies both in accordance with the degree of subcriticality and each measurement technique.