Evaluation of activation, inventories and dose rates induced by deuterons and neutrons along the RFQ and DTL parts of IFMIF Accelerator due to deuteron beam losses

The present report summarises the main features of the methodology approach developed for this assessment and its application to the IFMIF accelerator parts: the RFQ (Radio Frequency Quadrupole), that accelerates the deuteron beam up to 5 MeV, and the DTL (Drift Tube Linac) that accelerates the deuteron beam from 5 MeV up to 40 MeV. The analysis points out that in the RFQ deuteron energy range the nuclear models used by MCNPX-2.5b code don’t produce secondary neutrons in the deuteron nuclear interactions with the RFQ copper structural material. This implies that there is no contribute to the dose rates outside the RFQ due to both secondary neutrons and prompt gammas. The maximum value of beam-off dose rate, due to the structural material activated by deuterons, is 5.6E-02 μSv/h at the surface of RFQ section 10 (5 MeV deuterons), value much less than 10 μSv/h, the maximum allowable dose rate limit for workers’ access. In DTL, the last Tank 10 (highest deuteron energy, 40 MeV, and highest deuteron lost current, 246nA) gives the largest values of dose rates at beam-on and beam-off phases. The total beam-off dose rate, that is significant for the ORE, calculated considering a continuous irradiation scenario of 1 year, is 3.25 μSv/h at 1 m from the tank surface and at 1 week of cooling time. The area around the accelerator can be considered a restricted access area for maintenance, with specific procedures for worker protection .