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ITER is the flagship fusion project, conceived as an experiment to select and develop the technologies for the first demonstration reactor, DEMO. Nuclear analysis is a core discipline in support of the design, commissioning and operation of the machine. To date, it has been conducted with increasingly detailed partial models, which represented toroidal segments of the tokamak. However, the limitations of this methodology became evident as estimates of quantities relevant to design, safety and operation showed unquantifiable uncertainties, which is a risk. Here, we present a detailed and realistic 360° MCNP model of the ITER tokamak called E-lite. We demonstrate the model’s usability and practicality. Two examples are used to illustrate qualitatively and quantitatively how it solves previously intractable problems with marked benefits for the future nuclear analysis of ITER, with applications to DEMO and future reactors. E-lite constitutes a milestone in the field of nuclear analysis in terms of realism in the evaluation of key quantities. The development of nuclear fusion reactors requires detailed nuclear analyses to ensure they run safely and effectively. These are currently typically done using partial models. Juarez et al. now present a complete 360° model of the ITER tokamak, which allows for more realistic and complete modelling of the system.

During the plasma pulses, the neutron-induced activation of the cooling water will produce an important contribution to the radiation levels in the ITER Tokamak Complex. The resulting radiation field has a complex spatial distribution due to the combination of decay and production of radioisotopes in the intricate cooling lines that feed the numerous systems inside and outside the bio-shield. An accurate estimation of the cooling water radiation field is necessary to ensure that the radiological zoning is respected. As of today, this issue has been studied using simple, manually defined geometries with limited representation of the tens of thousands of components that constitutes the cooling circuits. This work describes the first production of a realistic and up-to-date integral neutronics modelling of all the cooling systems containing activated water beyond the bio-shield. The work was enabled by the development of computerized geometry modelling techniques to automatically simplify and dimension the system components. An independent review of the method ensured the validity of the simplified model. Moreover, automated scripts produced the activated water radiation source associated with the geometry model. The latter was obtained by linking thousands of cylinders, representing the coolant volumes, in chains of MCNP cells that reproduced the paths of the water lines inside the Tokamak Complex and, eventually, by calculating the radioisotopes activity in each cell. This methodology greatly speeds up the modelling time, reduces the risk of human error and enables the representation of the Tokamak Cooling Water System radiation source with an unprecedented degree of realism.

In this work, the D1SUNED code has been used to characterize the shutdown dose rate (SDDR) in the ITER Upper Port (UP) interspace due to activation induced by two neutron sources: plasma prompt neutrons and 17N decay neutrons emitted from the activated cooling water conducted through the UP. Furthermore, shielding measures have been proposed to mitigate the SDDR in the UP interspace; a set of conceptual shields has been designed and inserted into the MCNP computational model C-lite v2 covering the Vacuum Vessel UP Stub Extension and the UP Connecting Duct. The results have shown that the integration of proposed shields has significantly decreased the SDDR due to the activation induced by plasma prompt neutrons, while the activation induced by 17N decay neutron has a negligible contribution to the total SDDR in the ITER UP interspace.

The depiction of the nuclear responses of the ITER European Test Blanket Modules (TBMs), Helium Cooled Lithium Lead (HCLL) and Helium Cooled Pebbles Bed (HCPB) is presented in this work. Following important components update, and important methodological advances, the nuclear heat and the tritium production have been revisited, giving new estimations 10% higher than the previous evaluation for nuclear heat in both TBMs and to 15% higher for HCPB T production. This has an impact on the thermo-mechanical design of the TBM and the tritium handling. In addition, the Shutdown Dose Rates in the respective port interspace have been characterized in local approach. It shows a performance that could imply compatibility with planned in-situ maintenance activities when analysed in global approach, an improvement with respect to previous evaluations.

ITER will be the largest Tokamak in the world, and it is expected to produce a total of up to 2.8•1027 neutrons during its operation. The Tokamak infrastructure will become radioactive as the machine operates, which is an aspect that needs to be considered in the design of the planed in-situ maintenance activities. The occupational radiation exposure (ORE) must be accounted for, and an ALARA program must be implemented to minimize it. It requires the determination and analysis of shutdown dose rates fields, the purpose of D1SUNED tool. Common to all Direct one-step-based approaches, this tool needs to be fed with a nuclear data set tailored for each problem and produced ex professo. In this paper, we characterize the radioactive inventory relevant for the ORE of ITER maintenance activities using ACAB activation code. The ITER reference irradiation scenario SA-2 and the cooling times of interest 105 s and 106 s are considered. A comprehensive list of typical materials has been studied with detailed impurities content. The nuclear data set covers 99% of the radioactive inventory of concern, and all the pathways responsible for 99% of its production. It has been prepared following the ITER recommendations of cross-sections libraries and it has been verified against Rigorous-two steps calculations. This batch of nuclear data complements D1SUNED for shutdown dose rate exhaustive analysis for ITER with the perspective of maintenance according to the latest ITER nuclear data standards.

The neutron fields alter the radioactive inventory of the irradiated materials leading to subsequent decay photon fields. In some cases, these fields are of relevance either intended or undesired, normally involving safety and economics aspects. The determination of these fields can be of paramount complexity if high spatial resolution is required. The determination of these fields requires both radiation transport and activation calculations. The Direct-one-Step methodology, under the assumption that the radioactive inventory activity is lineal with the neutron flux, can address the problem with only one coupled neutron-photon transport calculation. In this paper the D1SUNED code for the calculation of decay photon field and related quantities using D1S methodology is presented. Calculation capabilities including the determination of 3D decay photon sources, filtering options, and other relevant features are presented. In terms of computational load, D1SUNED, which is based on MCNP5 code, presents improvements with respect to MCNP. It can save a 79% of the RAM memory used to store the geometry, a 98% of the loading time, and an acceleration of a factor two by controlling the decay photon emission, boosting the simulations for ITER-like problems. D1SUNED has been validated with the FNG benchmark experiment considering the null hypothesis rejection test and the C/E ratio with very positive results. As a consequence, D1SUNED has become a reference tool for the design of ITER, and other relevant nuclear fusion facilities.

The ITER equatorial port plugs are submitted to a drained weight limit of 45 T. This limitation can conflict with their radiation shielding demands, although some weight margin is being discussed. The port interspaces are subject to a shutdown dose rate limit of 100 µSv h−1 after 106 s of cooling time. To meet it, the port plugs must show a neutron flux attenuation comparable to their neighborhood, despite considering penetrations to host systems. Most of this task relies on the drawer shield module (DSM). In this work, two DSM concepts are analyzed with this perspective: the box-based DSM and the modular DSM. Regardless the penetrations, the box-based DSM leads to unsatisfactory port plugs to meet both weight and SDDR requirements. On the contrary, the modular DSM shows a performance which allows for the adoption of such DSM concept, or equivalent, a port may comply with both requirements at the same time, provided the penetrations are well designed.