J. Raeder

Report on the European safety and environmental assessment of fusion power (SEAFP)

Abstract The Safety and Environmental Assessment of Fusion Power (SEAFP) is being undertaken for the Commission of the European Union (EU) in the framework of their fusion programme. It was initiated in response to a recommendation of the European Fusion Programme Evaluation Board, which, under the chairmanship of U. Colombo, prepared in July 1990 the report “Evaluation of the Community Fusion Programme 1984–1990”. This recommendation emphasized the importance of safety research within the EU fusion programme and requested a more significant role for European industry in this area. On the basis of the tokamak concept, models of fusion reactors/power plants are being developed. This is done to the extent deemed necessary for credibility and for safety analyses, which must be robust in the sense that they do not overly depend on design details. One reactor model puts emphasis on low-activation materials, on the avoidance of hazardous chemical reactions and on the achievement of a reasonable overall plant efficiency. Another model emphasizes nearer term technologies and materials. To provide the substance for the outline design and for the related analyses, 11 model (M) tasks and 13 analysis (A) tasks have been defined. They have been allocated to the SEAFP participants: NET Team, UKAEA, a grouping of European industry (EFA-TGE), other European fusion laboratories, JRC Ispra, and the Canadian fusion programme. The M tasks cover the specification of plasma parameters, plasma operation, safety approach, technical concepts and materials; outline design of the reactor components and systems; maintenance design and procedures; and the layout of the overall plant. The A tasks range from the identification of the relevant accidents via the related safety analyses, calculation of inventories, estimates of normal operation effluents, radioactivity confinement analysis, dose estimates and assessment of radioactive waste to proliferation issues, materials resources and fusion-specific non-nuclear hazards. After an overview of the study concept and its implementation as a coherent European undertaking, the paper proceeds to safety concept, outline design (including parameters and materials) and overall plant layout. In accordance with the SEAFP schedule, the report on the safety assessment is limited to accident identification and to an outline of the analyses in progress.

LOCA, LOFA and LOVA analyses pertaining to NET/ITER safety design guidance

Abstract The analyses presented pertain to loss of coolant accidents (LOCA), loss of coolant flow accidents (LOFA) and loss of vacuum accidents (LOVA). These types of accidents may jeopardise components and plasma vessel integrity and cause radioactivity mobilisation. The analyses reviewed have been performed under the assumption that the plasma facing components are protected by a carbon based armour. Accidental temperatures and pressure transients are quantified, the possibility of reaction products combustion is investigated and worst case accidental public doses are assessed. On this basis, design recommendations are given and design features such as low plasma facing components armour temperatures (on almost the entire surface) and inert gas adjacent to the vacuum vessel have been implemented.

Net safety analyses and the European safety and environmental programme

Abstract The introduction outlines the Safety and Environment (S+E) part of the European Fusion Technology Programme and its relation to the NET device. The safety of NET proper is presented in terms of energy and radioactivity inventories, accident analyses, dispersion of radioactivity in the environment, radioactive wastes, and implications of component handling. The European S+E Programme is reflected by the expansion on these topics, as to a large extent, the basic information and quantitative results used have emerged from the collaboration between the European laboratories and NET under this programme. Where appropriate results acquired by the worldwide fusion community have been included to widen the understanding of the S+E aspects to be observed in the design of next generation fusion devices with burning DT plasmas.

Safety analysis and radioactivity confinement for ITER

Abstract The paper summarizes the main results of an collaborative effort by the ITER safety group (within the Systems Project Unit). The work was done in support of ITER design and evolved in collaboration with the other ITER groups. A safety approach has been defined and radioactivity dose limits have been quantified both in terms of target numbers for the design and of estimated limits expected to be requested by the regulatory bodies. Doses due to normal operation effluents of tritium and activation products have been estimated. Accidents of significance have been identified. Emphasis of accident analysis was put on events related to plasma (vacuum) chamber and cooling system. A confinement concept has been specified and assessed in terms of effective release fractions for accidental situations involving mobilization of both tritium and activation products. The masses of decommissioning and operational radioactive waste have been estimated and broadly characterized by the potential disposal options. Overall, the safety work resulted in safety features implemented in the design, recommendations pending for the EDA, and identification of potential problems to be resolved by EDA safety work as well as by safety related R&D.

Progress in the development of a first wall (FW) for net

During the initial physics phase of the development of a first wall (FW) for NET, an extensive plasma side protection of the steel FW structure was adopted in order to avoid damage by disruptions. Several novel protection concepts have been studied utilizing mechanically attached tiles in carbon based materials, which have demonstrated good performance in the present tokamaks. The FW structure in austenitic stainless steel is manufactured by electron beam welding and cooled by doubly contained low pressure water in order to achieve a reliable minimum leakage solution. For FW concepts with radiation cooled tiles, the permitted peak surface heat fluxes are limited by the tile temperatures to about 1 and 0.5 MW/m 2 for the physics and later technology phases, respectively. These heat fluxes are 2–6 times higher than the fatigue limits of other FW concepts with or even without protection. Hence, radiative tiles appear to provide robust protection against both disruptions and high normal heat loads. In order to demonstrate a credible FW design by 1990, emphasis is now being given to the manufacture and thermo-mechanical testing of prototypical FW test sections.

Lessons Learned from the ITER Safety Approach for Future Fusion Facilities

Safety has been an integral part of the design process for the ITER project since the conceptual design activities of the project. The safety approach implemented in the current ITER-FEAT design and the complementary assessments to be documented in the Generic Site Safety Report (GSSR) can provide valuable lessons for future fusion facilities. This paper summarises the ITER-FEAT safety approach and the assessments underway with a view to identifying key issues that have arisen and may have implications for such facilities. This paper discusses how these issues arose and are being addressed in the ITER project.

Extension of ITER waste assessment

The results, in terms of tons of radioactive materials and waste, reported in Volume V of the ITER Generic Site Safety Report (GSSR) were based on data available from the beginning of 2000 until spring 2001. However, some data of importance have been revised by ITER IT since GSSR was issued as well as aspects of importance have been addressed and investigated further.