Assessment of occupational radiation exposure for two fusion power plant designs

An assessment of the occupational radiation exposure issues of the fusion power stations has been performed focusing on the primary heat transport system (PHTS) of safety and environmental assessment of fusion power (SEAFP) reactor models. Fuel cycle systems have been considered for completeness, but not assessed. Fission reactor experience and fusion power reactor studies formed the basis of this assessment. Four assessments were performed. Two were based on SEAFP models 1 and 2, and the other two were based on improvements of these models suggested by an as low as reasonably achievable (ALARA) review. The following main conclusions are drawn from the assessments. The PHTS dose estimated for SEAFP model 1 (about 300 p-mSv/a) is below the current fission industry norm (about 500 p-mSv/a), but it is not ALARA. An ALARA value of 130 p-mSv/a is achievable and would be a reasonable target for the PHTS. The PHTS dose estimated for SEAFP model 2 (about 3000 p-mSv/a) is well above the current fission industry norm. Some design measures have been identified, that can reduce this dose to about 1200 p-mSv/a. While this is a substantial reduction, it is still well above the fission industry norm, therefore, additional effort is needed to obtain further reductions. The large difference in heat transport system doses between model 1 and model 2 is due to two main factors, the coolant and the coolant tubing material. The helium coolant eliminates the presence of corrosion products, and the vanadium alloy reduces the sputtering rate.