Monte Carlo based operational and shutdown dose rate calculations of HT-7U tokamak

The superconducting tokamak HT-7U will perform D–D plasma experiments and the production rate of 2.45 MeV neutrons will achieve the level of 1015 n/s. The dose rates during operation and after shutdown of HT-7U have been calculated based on a detailed three-dimensional model with the Monte Carlo code MCNP-4C, the inventory code FISPACT and the FENDL-2 nuclear data library. The so-called R2S method was used to perform the shutdown dose rate analyses. The results confirm that personnel access into the tokamak hall must be prohibited during operation. In addition the results show that the dose rate level near the outer wall of the tokamak hall slightly exceeds the dose limit. Additional shielding may be required. The shutdown dose rates of various experimental campaigns have been calculated and the waiting times for personnel access into the hall have been assessed. The results indicate that the in-vessel components of HT-7U will be considerably activated by neutrons and the shutdown dose rate level around the machine after long D–D plasma discharges is serious within a certain range of cooling time regarding the maintenance work.