Developping European research into Very High Temperature Reactors (VHTR).
RAPHAEL - ReActor for Process heat, Hydrogen And ELectricity generation - is an international cooperation project of the European Commission's 6th RDFP (Research & Development Framework Programme) in which the IRSN is participating. Pursuing the work begun by several smaller projects supported by the EU since 1998, the RAPHAEL project began on 15th April 2005 to last 4 years. The aim of the project is to conduct research and development actions supporting the design of an innovative nuclear fission system for the next generation IV of nuclear reactors, the Very High Temperature Reactor (VHTR). The VHTR technology, an evolutionary concept of the HTR technology, would allow the production not only of electricity but also of industrial heat and hydrogen without emitting CO2. It could find applications in the chemicals industry, the desalination of seawater and urban heating.
Coordinated by AREVA NP, the project involves thirty five organizations from ten European countries involved in HTRs: manufacturers, operators, universities, and research organizations.
The principal objectives of the RAPHAEL project were:
To provide the elements necessary for the verification and validation of the tools and the calculation models.
To evaluate the behaviour and performance of the fuel (special fuel of the TRISO type - TRistructural ISOtropic - comprising a core and coating materials) in normal operation and in accident situations at temperatures exceeding 1600 °C.
To analyze the behaviour of the spent fuel in storage conditions.
To develop innovative technologies for the system components, more particularly by exploring the interfaces with the production of hydrogen or utilization of the heat.
To develop an acceptable nuclear safety approach.
To integrate all the results in order to provide preliminary evaluations of the concepts of VHTR plants coupled with hydrogen production processes.
Promote the HTR/VHTR technology as the primary option to ensure a sustainable energy supply for Europe in the future, and to organize educational actions to promote employment in this domain.
The IRSN was involved in four areas:
How the TRISO fuel evolves in terms of isotopic composition when irradiated – utilization of neutronic calculation codes and comparison with experimental results deduced from irradiations of bursts of particle in the HFR reactor in Petten (the Netherlands);
Modelling of the behaviour of the fuel when irradiated on the basis of the above experimental results;
Thermohydraulic modelling of the helium circuit - utilization of the CATHARE
code – Gases in the framework of the benchmarking on the basis of transients conducted on the HE-FUS3 loop (ENEA, Italy);
A review of the behaviour of the fission products in the primary circuit of a VHTR (chemical forms, transport, deposition and interaction with dust) and analysis of the chemical forms of the fission products in the graphite.
Most of the IRSN's involvement concerns themes that were relevant for other reactor concepts, such as gas-cooled rapid neutron reactors.
Alongside this, the IRSN has participated in three meetings of the Safety Advisory Group created to assist the RAPHAEL project players in the orientations to choose: the SAG brings together a number of experts, some of whom belong to or act as advisors to the safety authorities (IRSN, US NRC, NNR in South Africa, etc.).
The results and prospects
The majority of the RAPHAEL project actions has ended in 2010, an extra year having been granted to all the projects but one, given the delay in the availability of experimental results.
Following on from RAPHAEL, the European project EUROPAIRS (End-User Requirements fOr industrial Process heat Application with Innovative nuclear Reactors for Sustainable energy supply), ended in December 2011, had the objective of defining the specifications and development programme for a VHTR demonstrator coupled to an industrial process. This step had been defined in the SNE-TP platform and has contributed to the continuation of VHTR research. The IRSN had put forward its candidacy to participate in certain actions of this new project.
The Raphael project provided the IRSN with the opportunity to test, for HTR fuel, patterns of behaviour of fission products developed for PWRs. It also allowed for an update on the available data regarding primary circuit fission product behaviour. This research was also based on the comparison of the irradiation experiment HFR-EU1 results, conducted in the HFR Petten reactor, with digital simulations (RSFF facility and Mephista database). The results on this point concerning the use of PWRs are encouraging, but there is still much physical evidence to be gathered. The IRSN has issued suggestions in this area with a view to future experimental irradiations. The Raphael project has also highlighted the lack of precise data on the diffusion of certain radionuclides through the HTR fuel container.
With regard to the calculations of how fuel evolves, the results remain relatively disperse. The Archer project will provide the opportunity to progress in this area.
Finally, discussions concerning the approach to safety, through contact with foreign experts, have facilitated the understanding of the specific features of the concept, such as the investigation of the efficiency of passive systems, as well as containment management.