Speaker
Description
Radiological dose mapping in the IFMIF-DONES accelerator system poses a demanding neutronics problem because the radiation field is not governed by a single source term, but by the superposition of multiple contributions with different physical origins and spatial distributions. During beam-on, biological dose and absorbed dose in silicon are largely driven by neutrons and photons produced in deuteron interactions with structural materials along the accelerator line, together with source contributions associated with the lithium target system. During beam-off, the radiological field is determined by decay-photon sources arising from activation in irradiated components and surrounding structures. A consistent treatment of these source terms is therefore required to obtain reliable dose maps for shielding design, radiological accessibility, maintenance planning, and assessment of risks to sensitive equipment.
In this work, a comprehensive methodology is presented for the calculation of beam-on biological dose, beam-on absorbed dose in silicon, and shutdown residual biological dose distributions in the IFMIF-DONES accelerator system. The approach is based on detailed MCNP neutronics models combined with dedicated source treatments for the relevant prompt and decay radiation contributions. A major difficulty in accelerator radioprotection calculations involving light ions is that deuteron-induced nuclear reactions in matter produce a very low number of secondary particles per primary history, so that direct Monte Carlo transport of the resulting neutron and photon fields becomes statistically inefficient and often computationally prohibitive. This difficulty is especially relevant when secondary source production is distributed along extended beamline regions and must be coupled to complex facility geometries.
To address this problem, the UNED-developed source methodology srcUNED-Ac is used to generate and transport secondary-particle source terms associated with distributed deuteron losses along the accelerator line, enabling an efficient evaluation of neutron and photon fields arising from beam-loss interactions. Combined with the source contributions associated with the lithium target system and activation-induced decay sources, this methodology enables a consistent description of the radiological environment under both operational and shutdown conditions. The resulting spatial dose maps provide a comprehensive radiological characterization of the accelerator system and identify the most relevant regions for shielding optimization, ALARA-oriented access planning, maintenance strategy, and component protection. More broadly, the methodology demonstrates how advanced source-generation and transport treatments are required to perform statistically reliable dose mapping in fusion neutron source facilities.
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