A Preliminary Study on the Radiation Dose Distribution in the Hot Cell Environment of the Pyroprocess for Safeguards

Abstract

Pyro-processing has positive effects on management of disposal spent fuels by reduction of high-level radioactive waste and the effectiveness usage of energy resources. As well known, pyro-processing should be operated under high radiation environment in hot-cell structures. For the reliable safeguards system of pyro-processing, it was recognized that an evaluation of the radiation dose distribution in the hot-cell environment is necessary in order to determine which technologies or instruments can be utilized on or near the process as the safeguards are measured. In this study, the flux and dose distribution of neutron and gamma-ray on the surface of each process and in the hot-cell environment were calculated based on a hot-cell geometry and specification with simplified process modeling. Gamma-ray and neutrons in an air cell and two separated argon cells were simulated respectively using Monte Carlo N-Particle Transport Code (MCNP6). Contribution to flux and dose distribution by particle types was also analyzed. Information such as material composition and process specification provided by Korea Atomic Energy Research Institute (KAERI) were applied to the simulation. F2 tally and t-mesh with and without a dose conversion factor were used in order to obtain the flux and dose rate. In the calculation, particle history up to 5e7 was employed to minimize relative error, most of which was less than one percent. Results showed that the dominant contributor on the flux and dose distribution was gamma-ray both in the air and argon cells. Because of its significant impact, it seems that gamma-ray would be much more critical when considering safeguards system utilized in the hot-cell, whereas gamma emission by gamma-neutron reaction in which neutron source interacted with the process surface was negligible. It is typical phenomenon that the flux and dose rate abruptly increased as their distances got close to each process. The radiation level, both of the flux and dose rate, was higher in the air cell than argon cells because air cell contains more gamma sources of which the flux and energy were significantly higher than that of neutrons. Considering radiation-resistance requirements for instruments utilized in the hot-cell, simulation results indicated the gamma-ray shielding plays an important role. A viability assessment of the special structures for Non-Destructive Analysis (NDA) measurement and the various shielding design for radiation monitoring in the hot-cell would be followed as a further study