Development of Neutron Shielding Concrete Containing Colemanite and Peridotite

The present paper describes development of Neutron shielding (NS) concrete and its application to the shield for a neutron spectrometer, SPICA at BL-09 beamline of J-PARC (Japan Proton Accelerator Research Complex). NS concrete is a new concrete using colemanite and peridotite rocks as an aggregate of concrete to build a compact and low-activation shields in the facilities of the high energy particle accelerators, instead of conventional radiation shields composed of normal concrete and some kinds of shielding materials such as a boric acid resin, polyethylene and/or iron. The shielding performance of the present NS concrete was evaluated with the Monte Carlo code PHITS and clarified through the transmission experiments by using 252 Cf spontaneous fission source. Additive mechanical and chemical tests showed better properties than those of the normal concrete. The present concrete was applied to the SPICA shields of a 52 m long neutron beam line and a neutron scattering room. Simplification of the shields and much shield thickness saving was attained comparing with a conventional shielding design. The shields were constructed in September 2011. It was also clarified in calculation that the neutron-induced activities in the NS concrete applied to the shields for a BNCT (Boron Neutron Capture Therapy) facility are several order magnitude lower than those even in the limestone concrete.