Development of an MCNP based direct one-Step (D1S) code for evaluation and mapping of shutdown dose rate in decommissioning of nuclear power plant

Abstract

The shutdown dose rate induced by the radionuclides produced during the operation should be evaluated to establish the decommissioning plan and to ensure the safety of the workers. However, it is virtually impossible to evaluate the shutdown dose rate in large facilities through the existing Rigorous 2-Step (R2S) method, such as nuclear power plants, due to the limitations resulting from its own calculation methods. Therefore, the Direct One-Step (D1S) method proposed in the ITER project was applied to the NPPs to perform the shutdown dose evaluation. The D1S code was developed based on MCNP and nuclear data was produced for D1S calculation. In addition, the time correction factors were calculated to correct the activities of radionuclides according to the operation and decay histories. To verify the developed D1S code, the estimated dose rates were compared using the R2S method and the relative error was approximately 1.2%. Furthermore, the D1S code was improved to be able to create the dose distribution map and the dose maps were displayed for the containment building of the Kori unit-1.