Hybrid Monte Carlo approach for accurate and efficient shutdown dose rate calculation

A novel approach has been developed for accurate and efficient shutdown dose rate (SDDR) calculations on fusion reactor devices. The new approach is based on an assumption of linear relationship between the mono-energetic neutron flux and the decay gamma source, thus the coefficients between them can be obtained for every materials and neutron energy groups through an inventory calculation. These coefficients are used in an extended version of MCNP code to perform decay gamma transport calculation. Decay gamma generated in multiple cooling time steps can be simulated together with the neutron transport calculation. This new approach has been successfully verified through the comparison with the JET shutdown dose rate measurements, R2S and D1S results. The results obtained demonstrate the reliability and efficiency of the new approach in estimation of the SDDR in fusion devices.