Neutron shielding and low-activation characteristics of borated concretes

Abstract

This thesis aimed to investigate an effect of polymer aggregate on the mechanical and neutron perfor-mance of borated low-activation concrete. Computational and experimental studies were conducted to investigate the neutron shielding and activation characteristics. Mechanical properties were also investigated with different boron and polymer contents. The Monte Carlo simulation code MCNP-5 was employed to determine the transmission of neutron through concrete at different energies, from 0.025 eV to 1 MeV, and the result from 0.025 eV was compared with experimental data from HANARO Ex-core Neutron irradiation Facility. It was shown that the replacement of polyethylene in borated concrete greatly enhanced the shielding efficiency of the concrete in high energy neutron shields. The epithermal and fast neutron attenuation property did not highly depend on the boron amount but was improved by the polyethylene replacement. The activation characteristics of the concretes were estimated with ORIGEN-S code and cross section data from ENDF/B-VI. The radioactivities of concrete were calculated in 1 KeV and 10 KeV neutron sources. Obtained activity of polymer-aggregate replaced borated concretes were sufficiently low comparing to the borated concrete and ordinary concrete. The reduced activity level can be explained by (i) improved neutron shielding effectiveness and (ii) lowered contents of radionuclides as polymer replaces fine aggregates. As hy-drogen and carbon elements of the polyethylene aggregate play a role as a neutron moderator inside the shielding concrete, the neutron-capture performance of elements, particularly the performance of boron could be improved. Furthermore, a double-layered structure, with the first layer of polyethylene aggregate replaced concrete and the second layer of 2 wt% borated concrete, showed significant improvement of shielding efficiency compared to monolithic structure. The mechanical properties of flow, density, absorption rate and co...