Measurements of prompt fission -rays from the reaction U ()

Makii, Hiroyuki   ; Nishio, Katsuhisa   ; Nishinaka, Ichiro; Hirose, Kentaro  ; Orlandi, R.  ; Smallcombe, J. ; Lguillon, R.; Sekimoto, Shun*; Takamiya, Koichi*; Otsuki, Tsutomu*

The Japanese government has a plan to remove the melted reactor fuel for the full deconstruction of Fukushima I Nuclear Power Plants, which have been seriously damaged in the Great East Japan Earthquake. The removal of the fuel must be carried out without reaching the criticality of the fuel. However, it is quite difficult to detect prompt neutrons accompanied by fission to monitor the increased fission rate due to the background -rays from the fission products in the fuel. On the other hand, the spontaneous fission of Cf shows a high energy -ray component around = 14 MeV, which is significantly larger than that for the background -rays from the fission products. We are proposing to develop a system based on the use of the high energy -rays accompanied by fission. In order to design the system, it is essential to know the spectrum of prompt fission -rays up to more than 8 MeV for thermal neutron-induced fission of U. However, no data are available in the energy range larger than 7 MeV. This prompted us to make a new measurement to extend the known prompt ray energy spectrum up to 20 MeV. In this contribution, we will present the results of a test experiment to know the measuring condition such as background -ray yield and spectrum.