International Fusion Materials Irradiation Facility-DEMO-Oriented NEutron Source (IFMIF-DONES) is a high-intensity neutron irradiation facility for qualification of fusion reactor materials, which is being designed as part of the European roadmap to fusion-generated electricity. Its main purpose is to study the behavior of materials properties under irradiation in a neutron flux able to simulate the same effects in terms of relevant nuclear responses as those expected in the first wall of the DEMO reactor which is envisaged to follow ITER. It is thus a key facility to support the design, licensing and safe operation of DEMO as well as of the fusion power plants that will be developed afterwards. The start of its construction is foreseen in the next few years. In this contribution, an overview of the IFMIF-DONES neutron source is presented together with a snapshot of the current engineering design status and of the relevant key results achieved within the EUROfusion Work Package Early Neutron Source (WPENS) as part of the 2014–2020 EURATOM Research and Training Programme, complementary to the EU Horizon 2020 Framework Programme (FP8). Moreover, some information on the future developments of the project are given.

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.

Fusion technology is progressing consistently, as evidenced many ongoing private and public initiatives, with long pulse projects like DEMO where materials behaviour is an important issue to address. To support the development of materials capable of tolerating the extreme conditions expected in future fusion reactors, the construction of the IFMIF-DONES facility has been planned. One of its systems are the Lithium ones, which includes the Primary Loop System responsible for supplying liquid Lithium to obtain the high flux, fusion-like neutron source to test materials. Since liquid Lithium is a hazardous material, emergency draining strategies are required to mitigate the consequences of emergency shutdowns and loss-of-coolant accidents (LOCAs) in the loop. There are currently two different draining strategies under consideration. The first strategy, referred to as Strategy 1, is based on maintaining the dump dank of the loop under near-vacuum conditions. The created pressure difference, together with gravity effects, allows the lithium to drain fast towards the dump tank. In contrast, Strategy 2 introduces a high-pressure argon injection system designed to push the lithium into the dump tank, which stays at a higher pressure.To compare the proposed draining strategies, a detailed model was developed using the MELCOR code. A validation exercise demonstrated that MELCOR is capable of accurately reproducing lithium transport under the expected IFMIF-DONES operating conditions. An additional exercise based on the subcooled Henry–Fauske model confirmed that draining velocity remained below the speed of sound in the two-phase mixture, excluding the appearance of complex-to-simulate choked flow phenomena.Then, both strategies were evaluated under non-LOCA and LOCA emergency shutdown, considering different parameters, like pipe dimensions, break sizes and locations and delay of actuations. The results show that, under emergency draining conditions, both strategies provide very similar performance, with Strategy 2 draining the lithium inventory approximately 12 seconds faster than Strategy 1. However, under LOCA conditions, Strategy 1 presents a clear advantage, reducing the leaked lithium inventory by approximately 20% to 45% compared to Strategy 2. Additionally, increasing the diameter of the draining pipes significantly improved the draining process while further reducing the leaked lithium inventory.