The IFMIF-DONES (International Fusion Material Irradiation Facility-DEMO Oriented NEutron Source) facility is being designed with the general objective of providing irradiation of representative samples of power fusion machine materials under prototypical conditions. A linear accelerator will deliver deuterons at high intensity to circulating lithium in a loop, which will produce neutrons capable of obtaining the required damage conditions. As a result of this process, radionuclides will be produced as a by-product, which is characterized by several degrees of mobility. Shielding and radiation protection measures will be required in the facility. IFMIF-DONES will be classified as a first class radioactive facility according to national regulations, with Spain being the European candidate to site the facility. Several aspects of the main safety instructions affecting the facility’s design are explained and discussed in this paper.

Integration of safety aspects in IFMIF-DONES design is a main objective of EUROfusion and European Commission projects. IFMIF-DONES will be a radioactive facility of the first category, and stringent safety objectives must be achieved and demonstrated. A very low acceptable risk for the worker, the public and the environment is the main principle in the design phase. The progress of safety activities is performed iteratively as detailed engineering develops, taking into account the uniqueness of the facility: a high-power deuterons accelerator (125 mA, 40 MeV), a target of flowing liquid lithium, traps for activation products, a dedicated-design module for irradiated samples, a massive shielding cooled room with confinement function, and a number of conventional systems with safety functions. Several phases are developed: (i) identification of sources and materials at risk, radioactive and nonradioactive, subject to potential mobilization, (ii) failure mode analysis and effects of systems, starting at the functional level, and support with probabilistic analysis, (iii) identification of scenarios leading to unacceptable risk if unmitigated, (iv) proposal of layers of defense by means of safety-credited components and design features, (v) deterministic analysis of scenarios in support of requirements, and (vi) definition and demonstration of safety requirements charged to components.

The IFMIF-DONES (International Fusion Materials Irradiation Facility – DEMO Oriented Neutron Source) is designed to reproduce neutron irradiation conditions in a fusion reactor. In this setup, a 5 MW deuteron beam collides with a liquid lithium target flowing at 15 m/s and maintained at 300°C. The resulting deuteron-lithium stripping reactions produce high flux neutrons with an energy spectrum comparable to that of future fusion reactors, thereby enabling testing of fusion-relevant materials, under controlled and homogenous conditions. A key component of this facility is the target assembly, where the ion beam interacts with the free surface of the liquid lithium target, which must maintain a thickness of 25 ± 1 mm to safely absorb the beam energy and minimize the neutron flux losses. This region of the facility is subjected to intense radiation, high temperatures, and lithium evaporation, making real-time diagnostics a challenging task. To address this hazard conditions, a radar-based system operating in the millimeter-wave (mmWave) range has been proposed. This system is able to continuously monitor the lithium thickness and to detect flow instabilities, interfacing with the Machine Protection System (MPS) to enable fast beam shutdown if the critical thickness is compromised. For initial technology feasibility tests, a commercial radar kit operating in the same frequency range planned for IFMIF-DONES has been acquired. Preliminary experiments include static-target tests that evaluate distance accuracy and material reflection characteristics using metallic and dielectric plates, followed by dynamic-target tests using water and liquid metals to simulate possible disturbances in the lithium flow. These experiments will validate the technology viability proposed as a solution for the fast MPS system and for quick monitoring of the Li surface homogeneity before implementing it in a real liquid lithium loop of IFMIF-DONES facility.