An Investigation into the Radiological Shielding and Dose Distribution of Containers for Transportation of Intermediate Radioactive Waste of Boushehr Nuclear Power Plant

In operation of nuclear power plants, significant amounts of radioactive wastes are produced annually so that it is necessary to determine special ways for transportation and disposal of the radioactive wastes. According to the related standards, containers for transportation of radioactive materials should be designed in such a way that the equivalent dose rates on the outer surface and at a distance of 2m from the container do not exceed 2mSv/hr and 0.1mSv/hr, respectively. The purpose of this research is to design a radiological shielding for containers to transport the group II radioactive wastes of Boushehr Nuclear Power Plant. The dose distribution calculations and the container design were implemented through the Monte Carlo method using MCNP5 code. The code was run by the use of 8 processors in a parallel way. The total activity of one drum and inventory density were estimated to be 4.248 Bq and 2000 kgr/m3, respectively. A steel drum with a dimension of 79.5cm in height, 28.55cm of radius and 0.3cm in thickness was filled with the cemented inventory. The dose distribution for the bottom rest wastes was calculated. The simulation result showed a value of 15.67mSv/hr for the equivalent dose rate on the surface of the drum. The result was 10% higher than the FSAR prediction. In order to decrease the dose rate, 3 leaden packages with 4 drums in each were put on the trailer for the transportation. The suitable lead thickness for reducing the equivalent dose rate in order to meet the required standards for the lateral parts, floor and top were 2.2cm, 2cm and 1.5cm, respectively. With this calculated thickness, the equivalent dose rates on the surface and at a distance of 2m from the surface were 550µSv/hr and 94µSv/hr, respectively.