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European Gas Cooled Fast Reactor

Periodic Report Summary - GOFASTR (European gas cooled fast reactor)

Project context and objectives:

Fast reactors have the unique ability to be sustainable, not only by generating their own fuel, but by burning minor actinides to reduce the quantity and radiotoxicity of nuclear wastes. The latter ability enables fast reactors to burn the minor actinides that they produce as well as the minor actinides arising from legacy wastes and thermal reactors in the nuclear park. The Generation IV International Forum (GIF) identified six systems which merit development to achieve the goals of sustainability, proliferation resistance, economics and improved safety. Of these six systems, three are fast reactors, the gas-cooled fast reactor (GFR) being one of these.

GOFASTR concentrated on the GFR option with a view to developing the GFR as a more sustainable version of the very high-temperature reactor (VHTR), also one of the six Gen IV systems. The design goals for GFR are ambitious, aiming for a core outlet temperature of around 850 degrees Celsius, a compact core with a power density of about 100 MWth / m3, a low enough plutonium (Pu) inventory to allow wide deployment, a self-sustaining core in terms of Pu consumption and a proliferation resistant core that does not use specific Pu breeding elements.

The GOFASTR consortium consisted of 23 partners: 8 industrial organisations, 7 national research centres, 4 universities, 3 technical support organisations (TSOs) for regulators and 1 research centre.

The project was aimed at the development of the Gen IV GFR system through its viability phase. For GFR, the main issues are centred around the development of a suitable fuel and achieving the necessary diversity and reliability of the safety systems. GFR requires a robust fuel that can operate continually at high temperature and high power density whilst achieving good fission product retention and economically viable burnup. With regard to GFR-specific safety systems, unlike gas-cooled thermal reactors, GFR does not have a large solid moderator structure so there is little thermal inertia in the core structure. To limit the fuel temperatures, therefore, in fault conditions the safety systems have to supply a flow of coolant through the core with high reliability. The challenge in this instance is providing the reliability without compromising the economics of the system.

Many of the objectives of the GOFASTR project were strongly aligned with those of the Gen IV GFR system. Consequently, the structures of the GOFASTR design, safety and fuel work packages were aligned to those of the Gen IV projects. Objectives of the design and safety work packages (WPs) included demonstrating the viability of the basic designs of the reactor unit (including core and fuel subassemblies), safety systems, the balance of plant and the containment concept. The fuel and other core materials work package aimed at contributing towards the development of a robust fuel concept in terms of its structure, fissile compound and cladding material. Irradiation of test fuel specimens was beyond the scope of GOFASTR, but one objective was to perform the necessary development work for irradiation capsule design and preparation of the supporting safety documentation.

In addition, GOFASTR included generic safety studies to enable the TSO’s to become familiar with GFR technology and to make a positive contribution on licensing whilst maintaining distance from developing the design and safety case. Another objective of GOFASTR was to forge links with other European projects and initiatives. The most important of these was the Sustainable Nuclear Energy Technology Platform (SNETP) - GFR features strongly in its roadmap and in the European Sustainable Nuclear Industry Initiative (ESNII), which is proposed as the vehicle via which fast reactor elements of the SNETP roadmap are to be implemented. GOFASTR also featured a dedicated education and training WP which aimed to coordinate training of masters and Doctor of Philosophy (PhD) students and stage formal courses on GFR technology.

Project results:

The project aimed to progress the designs of the GFR core, primary systems and specific safety systems to the point where the viability of the system can be established. The studies undertaken included neutronics, thermal hydraulics and core mechanics, to demonstrate that a practical ceramic core can be produced and that it will be sufficiently robust to withstand handling and operation in a commercial power reactor. GFR primary system studies developed the concepts for the power conversion system and for the primary pressure boundary together with exploration of alternative concepts for the pressure boundary. Conceptual design studies for the experimental demonstration reactor, ALLEGRO, were performed with emphasis on the design and analysis of the different cores required.

An overall safety approach and probabilistic methodology were developed for GFR, as well as reliability and severe accident analysis to develop the requirements for the safety systems. Risk minimisation studies were performed for GFR, covering issues such as water ingress, rod ejection, concrete / steel vessel, and dynamic analysis of guard containment integrity under different depressurisation scenarios to assess potential risks and provide further design information. Results showed that it would be possible to eliminate a number of risks by design. Extended transient analysis was performed for GFR and ALLEGRO covering a number of accident scenarios to analyse system behaviour, relevance of the current plant protection parameters and identify threats to component integrity. The analysis confirmed that the current GFR design is reliant on the active protective measures and provided additional guidance for sizing of safety measures, whilst the current safety provisions in the ALLEGRO design were adequate in most cases and recommendations for further improvements were provided. A set of licensing and generic safety studies were performed based on the technologies currently favoured for GFR. The objectives were to assess the acceptability of GFR safety concepts in terms of current licensing requirements, to identify the most important transients for safety demonstration and to carry out independent safety studies relevant to the GFR concept.

A number of benchmarking and neutronic studies were performed to develop core neutronics, thermal hydraulic and transient analysis methods. Benchmark activities were performed based on experiments at the L-STAR/SL facility and tests at the helium-cooled HE-FUS3 facility using different codes and modelling solutions. The study provided several recommendations for the GFR and ALLEGRO transient analysis regarding the modelling of different aspects of the gas system dynamics.

Studies were performed to address some key issues on fuel and other materials needed for the deployment of ALLEGRO and its test assembly positions. Benchmark studies were done on the ALLEGRO ceramic fuel design and parametric tests suggest high sensitivity of the simulated fuel swelling to the input data, as well as the dominating impact of the gap size on fuel temperatures. Potential materials have been identified for the ceramic-based ALLEGRO fuel design, considering technology readiness and availability. Studies were performed to provide initial data for proposed irradiation tests to investigate carbide fuel swelling, where small fuel discs would be irradiated at well-defined temperatures in an MTR.

In addition to the normal work of the universities in educating and training young researchers, a specific education and training package on GFR (consisting of a workshop and a course) was devised to attract a wider audience of students and researchers.

Links were established between GOFASTR and the different consortia working on advanced reactor concepts within European Atomic Energy Community (Euratom), including links with other Euratom initiatives such as the SNE-TP and ESNII. GOFASTR also represented Euratom in the Gen IV GFR System steering committee and project management board.

Potential impact:

The results from the project are presented in 67 contractual deliverables, of which 18 have been identified as being Euratom's contribution to the Gen IV GFR system. The three main outputs from the project are the GFR viability report, the Allegro viability report and the fuel irradiation test preparation documents, all three of which are deliverables to Gen IV.

The objective of this project was to address the main challenges to the viability of the GFR system, particularly fuel development and primary system studies as well as performance and fuel handling operations for an all-ceramic core.

Allegro is being developed as a GFR demonstrator by the Czech Republic, Hungary and Slovakia. GOFASTR provides information on the design, safety assessment and viability to these nations to enable fabrication costs to be refined beyond the provisional costing developed within ESNII.

The top level goals of the GFR system are to provide a versatile, sustainable, competitive and safe nuclear energy system. These goals are in-line with the overall goals of Gen IV and the SNETP. This project is aligned closely with the Gen IV programme and the priorities of the strategic research agenda of the SNETP.

For the goals of the GFR system to be realised, it has to be demonstrated that GFR is a viable system. Whilst it is believed that the concept is viable, it must be demonstrated that detailed problems, such as establishing a fuel design that can work continuously at high temperature and high power density, and providing sufficiently robust decay heat removal systems, can be solved.

This project has:

(i) provided one of Euratom's ongoing contributions to the six Gen IV systems;
(ii) fulfilled the need, identified by the SNETP, for GFR and LFR systems to be developed as longer term alternatives to sodium cooled reactors; and
(iii) given researchers in all Member States the opportunity to contribute to Gen IV, particularly as most European nations are not signatories within the GIF.

Beyond the goals of the GFR system, the project has a major impact both in maintaining fast reactor technology within Europe and in extending this technology to nation states that have not had a historical association with the technology. In this respect, activities of GOFASTR are complementary to other European fast reactor projects and the ESNII. There has been significant effort made in GOFASTR to link with other Euratom activities, centred on collaboration with other Seventh Framework Programme (FP7) projects, participation in the ESNII and collaboration with the Central European Allegro consortium.

Education and training is an important route by which the technology will be maintained and developed, and the project has provided a variety of training opportunities. It is important that young engineers and scientists are exposed to challenging technical projects whilst at university to encourage them to take up careers within the nuclear industry and to develop them to be able to lead future research projects.

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