Decay Gamma Dose Rates in the EVEDA Accelerator: Impact of the Deuteron Loss Uncertainties in Accelerator Maintenance

Before starting with the construction of the International Fusion Materials Irradiation Facility, the objective of the Engineering Validation and Engineering Design Activities (EVEDA) phase will be to demonstrate feasibility of design. For this EVEDA prototype, analysis of the dose rate evolution during the beam-off phase is necessary for radioprotection and maintenance feasibility purposes. The key points for determining the dose rates of the beam-off phase are on one hand the neutron source produced along the accelerator beam line and on the other hand the deuteron losses giving rise to this neutron source.

A new methodology to compute the neutron source coming from the deuteron interactions with the intercepting material as well as with the deuterium previously implanted has been developed. This new procedure consists of evaluation of the low-energy deuteron-induced neutron source that is not calculated by most transport codes and assessment of the deuterium concentration evolution in the material, which is generally not taken into account in this type of calculation. The impact of this new approach on the neutron source and dose rate results is very relevant.

In addition, different sets of deuteron losses computed during the last 3 yr have been compared and used for neutron activation and dose rate calculations. The effect of the deuteron losses upon neutron source production and residual dose rates in the vicinity of the accelerator components is evaluated, and implications for hands-on maintenance activities are discussed. The impact of the differences in the sets of deuteron losses has been found to be very important for dose rate evaluations. Using the most recent deuteron loss information, we obtain dose rate values more than one order of magnitude lower than those obtained using the former data.