ELSEVIER Journal of Nuclear Materials 212-215 (1994) 1720-1723 Investigation of neutron shielding efficiency and radioactivity of concrete shields containing colemanite Yasemin Yarar Yddu Technical University Physics Department, 80270 Sisli, Istanbul, Turkey Ahmet Bayiilken Istanbul Technical University Institute for Nuclear Energy, 80626 Maslak, Istanbul, Turkey Abstract In this work, colemanite, a boron-bearing ore, was added to ordinary Portland concrete as aggregate. Some concrete blocks containing different amounts of colemanite were produced and their neutron permeability and compressive strength were determined. From the results of the experiments, taking into account the nuclear and structural properties of shielding material, a proper colemanite adding ratio was presented. A neutron transport calculation of the shield containing colemanite was made by using the removal-diffusion technique and the decrease in shield thickness, compared to ordinary Portland concrete, was found. Assuming a 20-year stepwise irradiation, the neutron-induced activity within the shield was calculated. Cooling time after shutdown was taken up to 10’ years. By comparing the total and elemental activities of the ordinary and colemanite-added Portland concretes, the contribution of colemanite to the shield activity was investigated. 1. Introduction In all nuclear installations, concrete is the most commonly used shielding material to protect from neu- tron radiation. It is a common practice to add boron to concrete in order to try to enhance the thermal neu- tron attenuation properties and to suppress secondary gamma-ray generation. Since pure boron is difficult to obtain by common extraction methods, the use of boron-bearing minerals is more economical and practi- cal [1,2]. 60% of the world boron reserve is found in Turkey. Among the minerals, colemanite (2CaO . 3B,O, 5H,O) and borax (Na,O. 2B,O,. lOH,O) have com- mercial importance. Because of the Na content, borax is not suitable for shielding purposes. Due to the high B,O, content, up to 51%, and low price, colemanite is more attractive for neutron shielding [3]. In the past, colemanite was used, with a maximum of 7 wt.%, together with some heavy aggregates such as barite, steel punchings or with some special cements such as lumnite, magnesium oxychloride [2]. However, non-conventional materials require special pouring and handling techniques, thus increasing concrete costs. Therefore, in this work, colemanite was used in larger amounts together with conventional materials to pro- duce an economical shield. 2. Experimental procedure and results To eliminate deleterious effects of colemanite, the following precautions were taken in the experiment: - Colemanite was ground in the form of a coarse aggregate. - The Portland cement dosage was chosen to be high to tolerate the drop in the mechanical resistance of concrete. - For the initial setting of concrete, blocks were kept longer in their mold under the condition of con- stant moisture. At a basis of an ordinary Portland concrete (OPC), 0022-3115/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SSDIOO22-3115(94)00204-2