Water cooled and gas cooled SEAFP fusion plant models comparison based on the outside-cryostat dose rates

The results of biological dose rate calculations for different locations in the vicinity of the concrete shield wall of the cryostat pit of the SEAFP-2 fusion plant are given in this paper. The Plant Model 3 (PM3) design (low-activation martensitic steel for first wall and blanket, Li4SiO4 as breeder material, helium cooled) is assessed and the results are compared with the corresponding ones related to the Plant Model 2 (PM2) design (low-activation martensitic steel for first wall and blanket, Li17Pb83 as breeder/multiplier material and water as coolant). Dose rates are evaluated both during plant normal running operation and after plasma shutdown before long-term maintenance activity. Contribution due to neutrons and gamma-rays are considered through a coupled n-γ Sn transport calculation. Effects of streaming are also evaluated. The dose rate values into pit cells result to be slightly higher for PM3 with respect to the PM2. In any case that area can be classified as ‘Green zone’, i.e. with unlimited access for radiation workers, according to the ITER zone classification.