Investigation on the attenuation neutron and gamma rays in reactor concrete biological shield

Abstract

The biological shield of a nuclear reactor is required to attenuate both neutrons and gamma rays from the reactor core. Generally, materials having high densities are used as bio 1ogica1 shie1d materia1s in a nuc lear reactor. Concrete has been widely used as shielding materials due to its satisfactory material strength and good shielding properties. The density of conventional ordinary concrete is not adequate for.a biologiGal shield in a nU,clear reaGtor. Types of concrete possessing high density, should be developed in order to attenuate both neutron and gamma radiation emitted from the nuclear reactor. The heavy aggregates such as barite, magnetite, ilmenite, limonite etc. have been widely used for preparing a high dens~ty concrete for-biological shield in a nuclear reactor. While fabricating the high density concretes, due consideration should be given to the local availability of the aggregates. Since the magnetite and ilmenite aggregates are available as -by products in the beach sand processing pilot plant at Cox's Bazar of the Bangladesh Atomic Energy Commission, this work was undertaken to design and fabricate high density concrete shields indigenously with the objective of avoiding costly imports and also to develop -local know how. In this study, high density concrete with and without boron additives using ilmenite and magnetite sand have been studied. For comparison, ordinary concrete with and without boron additives have also been studied. In addition, mixed conc~ete used in the biologic~l shield of 3 MW TRIGA Mark-II research reactor of the Bangladesh Atomic Energy Commission has been studied with and without bo~on additives for comparison with the other three types of concretes with and wihtout boron additives. The density, compressive strength, modulus of elasticity and splitting strength were measured for these concretes. The densities of ilmenite and magnetite concretes are found considerably higher than that of ordinary concrete. The nuclear parameters such as attenuation coefficient, removal cross section, half value thickness, and relaxation length, which are of interest for reactor shielding have been evaluated for these concretes with a spontaneous fission source (252Cf). The investigation concerning the attenuation properties reveals that the shielding properties of boron loaded heavy concretes are better than those of ordinary concretes and slightly better than those of heavy concretes without boron additives.