Neutron analyses and design of components for iter

Resumo

The objective of this thesis is contributing to the development of the ITER project. ITER is the largest Tokamak ever conceived and the fifth largest scientific project in the human history. It is funded by 35 countries, among which the European Union provides with half of the budget. ITER, which is currently in construction in southern France, is meant to demonstrate the scientific and technological feasibility of fusion energy for peaceful purposes. ITER will be the first Tokamak with an extensive nuclear phase. In the deuterium tritium phase, it will operate the plasma at 500 MW of power, leading to an intense radiation field resulting from the spreading of the plasma neutrons, and their interactions. The neutron field represents itself a challenge to the design. But it produces additional radiation fields, which are, at the same time, additional challenges. The design of the ITER project presents a problematic that relates a set of radiation sources with a set of design requirements and regulation. A genuine need for nuclear analysis of high quality exists. When the project started, the field was mostly developed for the fission industry decades ago. It was not ready to face the diversity and the complexity of the problems identified. For the last years, the methods and tools have evolved in parallel to the nuclear analysis and the understanding of the diverse phenomena. The work presented here is part of it. The work is structured in three major blocks. The first one deals with the tool ACAB. It is a computational code to determine the evolution of the radioactive inventory over time in the presence of a radiation field. It was conceived in the 1990’s and first applied to the design of the National Ignition Facility. The last version of ACAB code was released in 2008, and it has been used in different works to ITER designs since. As part of this work, the numerical method of the code has been re-assessed in view of the ITER specifics. Enhancement of the results robustness is sought. The second block of work has to do the production of geometry models for radiation transport with MCNP, and the production of one of the ITER reference models: the Tokamak Complex. Since the early 2000’s some tools appeared enabling, for the first time, to translate complex 3D geometries into MCNP. They have represented a revolution in terms of precision and detailing in the geometry production. But they have also meant a revolution in terms of time dedication for the setting up of the models. New procedures have been produced as part of this work in response. And they have been applied to the production of the ITER Tokamak Complex MCNP model. This important model incorporates the latest approved baseline of the three main 7-stories buildings of the project. It represents a complex of 120 m x 80 m x 80 m, with thousands of penetrations, dozens of rooms, doors, shielding, ventilation conducts, etc … The Tokamak Complex MCNP model, produced as part of this work, plays two fundamental roles in the ITER project. On the one hand, it has been used to assess the compatibility of the complex design with the electronics allocation in the different parts of the building. On the other hand, it is being used in the implementation of the ALARA strategy to determine the workers radiation exposure in maintenance tasks outside the bio-shield. It is one of the most complex MCNP models ever built, and its conception and implementation was consequently adapted. The third block of work is related to the ITER Test Blanket Modules (TBMs). Themselves, the TBMs encapsulate one of the three technical goals of the project: “The device should test tritium breeding module concepts that would lead in a future reactor to tritium self-sufficiency, the extraction of high grade heat and electricity production.”. The TBMs are experiments with relevant deployments of technologies aimed at breeding the tritium, while recovering the kinetic energy of the neutrons and enabling the heat evacuation. The European Union is responsible for the design of 2 out of the 6 TBMs that will be hosted in ITER. One of them considers the Helium Cooled Pebbles Bed concept, and the other the Helium Cooled Lithium Lead concept. In this work, both TBMs have been evaluated in terms of nuclear heat, tritium production and shutdown dose rates with an unprecedent level of detail and robustness. This package of information will be the basis for the preparation of the TBMs Preliminary Design Review, the next and second in a sequence of three independent reviews before manufacturing.