Application of the Monte Carlo method to estimate doses in a radioactive waste drum environment

During refuelling operation in a Nuclear Power Plant, filtration is used to remove non-soluble radionuclides contained in the water from reactor pool. Filter cartridges accumulate a high radioactivity, so that they are usually placed into a drum. When the operation ends up, the drum is filled with concrete and stored along with other drums containing radioactive wastes. Operators working in the refuelling plant near these radwaste drums can receive high dose rates. Therefore, it is convenient to estimate those doses to prevent risks in order to apply ALARA criterion for dose reduction to workers. The Monte Carlo method has been applied, using MCNP 4B code, to simulate the drum containing contaminated filters and estimate doses produced in the drum environment. In the paper, an analysis of the results obtained with the MCNP code has been performed. Thus, the influence on the evaluated doses of distance from drum and interposed shielding barriers has been studied. The source term has also been analysed to check the importance of the isotope composition. Two different geometric models have been considered in order to simplify calculations. Results have been compared with dose measurements in plant in order to validate the calculation procedure. This work has been developed at the Nuclear Engineering Department of the Polytechnic University of Valencia in collaboration with IBERINCO in the frame of an RD project sponsored by IBERINCO