Improvements of the Control Rod Material for Long Lifetime by the High Power Millimeter-wave Ceramics Sintering Method

Idehara, Toshitaka*; Mitsudo, Seitaro*; Hoshizuki, Hisanori*; Ogawa, Isamu*; Shibahara, Itaru; Nishi, Hiroshi; Kitano, Akihiro ; Ishibashi, Junichi

Boron Carbide B4C pellet is an important part of control rod used to control the reactivity of nuclear reactors. B4C pellet put in a nuclear reactor suffers heavy radiation damage and deformation, which result in a partial destruction and shorten the lifetime of B4C. It is important to improve the characteristics of the B4C pellets for extension of its lifetime. As the results, if the control rod without the shroud will be available, we can realize much simpler structure. In order to improve, the B4C pellet, which was sintered by the hot-press methods, we have re-sintered it by high power millimeter wave ceramics nano-indentation test. The increase of the plasticity is observed. The same improvement of plasticity was observed in alumina pellets that were sintered by millimeter wave sintering methods. Such results imply that the further improvement is expected, if the B4C pellet is sintered from powder specimen by the high power millimeter-wave sintering method. To simulate a partial destruction of B4C pellet under the thermal stress, preliminary internal heating experiments of B4C pellet are performed by using high power millimeter-wave. At the difference between internal and surface temperatures of 1000C, the partial destructions and small cracks are observed in B4C pellet. Thes may be a kind of model experiment for destruction of B4C pellet irradiated by neutrons.