R&D needs for near-term HTRs

Recently some high temperature reactor (HTR) projects evolved towards application to cogeneration of power and industrial process steam. Gas direct or indirect cycles, previously favored, are no longer appropriate for this application. For AREVA and other vendors, the present reference concept is therefore the steam cycle with a core outlet temperature not exceeding 750 °C. Because of the large development of this concept up to the 1980s in U.S. and Germany, present developments and risks will be minimized, but not eliminated. R&D and qualification remain necessary.Though many needs are common to different steam cycle designs, this paper focuses on R&D and qualification needs for AREVA block type design.There are different reasons why data from past programs are not sufficient: first, even for components or fuel concepts formerly demonstrated, adequate performance of their present implementation, with recreated design and manufacturing processes, might have to be shown. Moreover increased performance expected in some cases (fuel burn-up, reactor power) for economic competitiveness has to be demonstrated and might require design evolutions that need validation.Materials also require significant R&D. Qualification needs for present commercial graphite grades, different from past ones, and for new materials like composites are well known. But, with operating conditions different from LWR ones, new data might be needed even for usual materials, like the vessel material SA-508.Computer codes experienced large evolutions in last decades: more refined physical modeling, advanced calculation and software techniques. HTR design tools followed the general trend, and now some new experimental data might be needed for their qualification, as the qualification domain evolved (e.g. higher burn-up) and compliance of old data with quality standards is often no more traceable.Though in a first step HTR can simply substitute fossil fuel boilers for industrial steam supply without change in users’ applications, developments of materials, fuel and heat exchanger technologies for higher temperature will allow in the longer term widening the potential application market. But in that perspective some developments on the application side will also be needed: optimization of industrial processes for adaptation to specific features of HTR heat supply, heat transport technologies, heat exchangers for operation in severe environment, etc.Last but not least, the evolution of licensing requirements will force to reconsider some past demonstrations and solutions.There are conditions for this R&D to be useful for HTR industrial development:(1)A close coordination with design, for R&D to focus on relevant issues and to provide data in due time.(2)Availability of appropriate HTR specific R&D facilities, like irradiation rigs for fuel and materials or large helium loops that, for some of them, do not exist yet.

► For near term HTR meant at cogeneration of electricity and industrial process steam, R&D needs are minimized, but should not be neglected. ► Though steam cycle HTR technology is a proven technology, new developments should incorporate recent technology advances (e.g. NDE, material science, magnetic bearings, computer code techniques, etc.) and should address new safety requirements and new competitiveness challenges. ► The near term HTR technology is not a closed technology and should lead in the longer term to HTR with higher performance (in terms of temperature, fuel burn-up, etc.) as long as the corresponding R&D (materials, advanced fuel, intermediate heat exchanger, etc.) is not neglected. ► There is a high risk for R&D not to be relevant if launched blindly without referring to data needs from a specific design. ► R&D needs must take into account process heat user requirements and must not address only the nuclear domain, but also the application domain (process heat transport, process development).