Improvement in the design of shielding containers for intermediate-level radioactive waste

Abstract

The aim of this study is to improve the concrete shielding containers employed for the disposal of conditioned radioactive waste (RW), which is in the form of sorbents containing isotopes Co-60 and Cs-137. The application of additional shielding consisting of a metal shell with various fillers, intended to increase the total radioactivity of the conditioned RW included in a single concrete shielding container, is investigated based on the radiation safety requirements. This paper presents the simulation results of applying additional shielding for RW in protective containers with increased radioactivity capacity. Monte Carlo simulations are performed to estimate the dose rate generated by conditioned RW at a distance of 1 m from the container. The improved container has three areas. The outer wall, with a thickness of 15 cm, is made of concrete. The center of the container consists of a cylindrical shell made of a metal or an alloy, with a thickness of 0.5–3 cm, containing a sorbent saturated with cesium and cobalt isotopes. The influences of the material and the thickness of the shell and filler on the equivalent dose rate are studied. The average absorbed dose is found to decrease from 8.11E-19 Gy to 2.93E-19 Gy, and the equivalent dose is found to decrease exponentially from 1946.30 μSv/h to 704.35 μSv/h when the capsule thickness is increased from 0.5 cm to 3 cm, respectively. A 3-cm capsule made of 80PbO +20Zn is found to reduce the equivalent dose to 183.81 μSv/h.