[en] Modern HTR nuclear power plants which are now under development (projects GT-MHR, PBMR) are based on the direct cycle concept. This concept leads to a more important efficiency compared to the steam cycle but requires the use of high performance components such as an helium/helium heat exchanger called recuperator to guarantee the cycle efficiency. Using this concept, a net plant efficiency of around 50% can be achieved in the case of an electricity generating plant. As geometric constraints are particularly important for such a gas reactor to limit the size of the primary vessels, compact heat exchangers operating at high pressure and high temperature are attractive potential solutions for the recuperator application. In this frame, Framatome and CEA have reviewed the various technologies of compact heat exchangers used in industry. The first part of the paper will give a short description of the heat exchangers technologies and their ranges of application. In a second part, a selection of potential compact heat exchangers technologies are proposed for the recuperator application. This selection will be based upon their capabilities to cope with the operating conditions parameters (pressure, temperature, flow rate) and with other parameters such as fouling, corrosion, compactness, weight, maintenance and reliability. (author)

[en] Full text of publication follows. For industry, materials R and D needs are dependent on specific market prospects and on the possibility of going from laboratory results to industrial applications within a reasonable period of time. HTR can be considered in some cases for electricity generation, but the main incentive for this type of system is its possible use for industrial process heat applications without CO₂ emission. It is also the main challenge for its development, as there is no experience at all of a direct coupling of a nuclear heat source with an industrial process without intermediate conversion into electricity. The specifications of the system to be developed, in particular' but not only the operating temperature, will depend of the precise characteristics of these applications. As far as the operating temperature is concerned, there are many industrial applications with high heat consumption at temperatures significantly below 800 deg C and also other applications which require much higher temperatures. AREVA, together with its partners CEA and EdF, with the contribution of the European project RAPHAEL of the 6. Framework Programme and possibly in the future additional inputs from the VHTR materials project of the Generation IV International Forum, has undertaken a large R and D programme for assessing the potential of materials which can be available on an industrial basis for being used for critical HTR components, in particular the Intermediate Heat Exchanger (IHX), unavoidable for heat applications, the reactor vessel, the internals and the control rods. From the results already obtained, it appears that the materials which could be available for an industrial development as soon as possible (next decade) have performance limits that would not authorize operating temperatures much above 800 deg C. In the longer term, if real market needs are identified, more advanced materials could be considered, but it is clear that they require a lot of R and D, not only to optimise them and assess their performance, but also to develop processes for forming and assembling them, which, very often do not exist at all for the time being. Now the challenge is not only to develop and qualify high performance materials, but also to develop and manufacture high performance components made from these materials. Some of these components, in particular the IHX, are beyond the industrial state of the art, even if the aim is not to reach very high temperatures. Their development will require an extensive R and D and qualification programmes, which will necessitate large test facilities producing actual operating conditions (impure helium atmosphere, high temperature, transients). Therefore the priorities of the development programme should be put in the right order: first of all, to make the demonstration of industrial feasibility of the coupling of a large scale reactor with an industrial process heat application at a reasonable temperature level, and therefore to develop and qualify the materials and components needed for the reactor and the coupling, then, in the longer term, to search for solutions for higher performances in terms of temperature, fuel burn-up, availability, lifetime, etc., if required by the market. (authors)

[en] The aim of the study presented in this paper was to give some advice to the designers in order to improve the post-buckling stiffness of the roof slab's bottom plate during the HCDA. An experimental approach has been performed on representative test plates and the following parameters have been tested: (1) Number of pads between two stiffeners and then their density. (2) Distance between pads and bottom plate (d). (3) Level of residual pressure applied on the plate. The experimental results have been confirmed with 2D and 3D numerical approaches. It appears that for an important number of equidistant pads and a distance d = 5 mm, the post-buckling behaviour of the plate is significantly improved. On the other hand, sensitivity studies of the behaviour of the structures under dynamic loads (as compared to the static experiments and calculations) have recommended pads fixed with a 330 mm step. This arrangement is the minimum arrangement, it is possible to manufacture. As the buckling and post-buckling behaviour of the bottom plate of the roof slab is considered satisfactory for such an arrangement, it represents a solution for the conceptual design of a LMFBR roof slab. (author)

[en] The HTR-E European project (four years project) is proposed for the 5th Framework Programme and concerns the technical developments needed for the innovative components of a modern HTR with a direct cycle. These components have been selected with reference to the present projects (GT-MHR, PBMR): (1) the helium turbine, the recuperator heat exchanger, the electro-magnetic bearings and the helium rotating seal; (2) the tribology. Sliding innovative components in helium environment are particularly concerned. (3) the helium purification system. Recommendations on impurities contents have to be provided in accordance with the materials proposed for the innovative components. The main outcomes expected from the HTR-E project are the design recommendations and identification of further R and D needs for these components. This will be based: (1) on experience feedback from European past helium test loops and reactors; (2) on design studies, thermal-hydraulic and structural analyses; (3) and on experimental tests

[en] CEA, EDF and AREVA French partners launched a coordinated research program on Sodium-cooled Fast Reactors (SFR). Design works were performed within this guideline by the 3 partners for the reactor structures, including thermal-hydraulics and thermo-mechanical analyses. The concerned structures are the following. For the inner vessel different options have been investigated: the single conical Redan like the Phenix reactor inner vessel, variants of cylindrical inner vessel designs, together with more advanced options. For the core support structure, several options have been investigated: the dia-grid supported by a box core support structure like the EFR (European Fast Reactor project) design option and variants of the integrated core support structure. For the upper closures, metallic and concrete options for the roof slab and rotating plugs, together with different design options for the above core structure. This paper presents a status of the studies for these structures; the most promising design options are highlighted. These studies will be used as a starting basis for the demonstrator prototype ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration) pre-conceptual design, launched end 2010

[en] In France, a comprehensive research and development program is in progress, that relates to several fields (design studies, fuel, materials, codes, high temperature helium technology), for Helium GCR projects with both direct and indirect cycles. In this framework, High Temperature Heat Exchangers, such as the helium/helium recuperator or the Intermediate Heat Exchanger, are considered as key components for the overall efficiency of the system. Within a Brayton cycle, the Heat Exchangers (HE) have to work under very severe conditions (temperature, pressure, pressure differences between the circuits). Thus, no directly available compact technologies exist in the market. However some potential technologies (tubes, plate fin, printed circuit HE) have to be investigated. The main purpose of this paper is to present the methodology for the heat exchangers developments and qualifications. In addition, the main experimental test rigs are described as follows: · Analytical benches, at channel scale, for providing reliable data of thermal hydraulic correlations. · Small air loops, CLAIRE loop (~ 100 kW), at the mock-up scale, for testing different technologies and selecting the most promising one. Both thermal hydraulics and thermal mechanical (thermal cycling) aspects are concerned. · Technological validation (endurance tests), of the most promising technology under representative conditions of temperature, pressure and helium velocity, on a multi-purpose technological loop, HELITE loop (~ 1 MW). · Large helium facility (10 MW) for component qualification on model at scale 1. (author)

[en] Arising from the EU 5^th and 6^th Framework Programs (FP’s), the purpose of this paper is to present the achievements gained in the area of HTR & VHTR component development within the 5th FP HTR-E project and the future work activities to be realized in the frame of the new RAPHAEL project (6^th FP). The HTR-E R&D project started on 1st January , 2002 with 14 partners, from industry and research centres involved in HTR development: Framatome ANP, CEA, Zittau university, NRG, FZ Juelich, Empresarios Agrupados, NNC, Jeumont, S2M, Ansaldo, von Karman institute, Heatric, EV Oberhausen, Aubert et Duval. The work programme concerned the technical developments of innovative components of a modern HTR with a direct cycle, with references to industrial projects existing at the time (GTMHR, PBMR) for direct cycle HTR. The main tasks performed within the HTR-E Work Packages were as follows: • The helium turbine (WP1), the recuperator heat exchanger (WP2), the electro-magnetic and catcher bearings of the turbo-machine (WP3) and the helium rotating seal: dry gas system, fluid film barrier, canned magnetic bearings (WP4). Based on past experiences and specific calculations, design recommendations of such components were proposed. Experimental tests were also performed to validate the recommended concepts for electro-magnetic bearings and recuperator heat exchanger. • The tribology (WP5). Sliding innovative components in helium environment were particularly concerned (stator seals, control rod mechanisms…). The experience feedback was analysed and complementary tests have been carried out by CEA and Framatome ANP. • The helium purification system (WP6). This work package provided recommendations on impurity content in the helium atmosphere for a modern HTR in accordance with the materials proposed for the innovative components. (author)

[en] The (European) High Temperature Reactor Technology Network (HTR-TN) was created in 2000 by the main industrial and Research actors of nuclear energy in Europe for elaborating a strategy for developing advanced HTR technology towards industrial application and for taking initiatives for implementing this strategy, most particularly through the Euratom funded R and D programmes. HTR-TN members are convinced that the main market push for industrial deployment of a new generation of HTR will not come from utility needs for electricity generation, but from industrial process heat needs: even if HTR can be considered for satisfying particular niches of the electricity market, there will not be any incentive for utilities already experienced in the exploitation of large LWR to take the risk of a significant technology change, when no evident competitive edge would result from it. On the contrary, HTR is the sole nuclear system that can address heat needs of a large number of industrial processes that require a higher temperature than the temperature provided by all other types of industrial reactors. The possibility for HTR to address the industrial process heat market is a strong asset, as it opens to HTR a large market which is presently looking for solutions to reduce drastically CO₂ emissions, but at the same time it is a huge challenge: industrial exploitation of nuclear energy has been for the time being focused on electricity generation for which user requirements are relatively uniform. The versatility of process heat needs in terms of power, temperature, reliability, etc. will require a much larger flexibility of the nuclear heat source, which is not usual for nuclear industry, looking for competitiveness through standardisation. Therefore HTR-TN considers that the top priority innovation for HTR present development should not be missed: it is to demonstrate at an industrial scale the technical, industrial and economical feasibility of the coupling of a HTR with a process heat application, even at a reasonable temperature level ∼500-700 deg. C), and not necessarily to search for higher temperatures ∼ 800-1000 deg. C), which will be reached in the longer term, if there are significant market needs for such temperatures. After a period of 7 years dedicated to the development of base HTR technologies within several projects of the 5. and 6. Euratom Framework Programmes, HTR-TN proposes to launch in the 7. Framework Programme the development of a demonstrator coupling a HTR with an industrial process heat application. Such a development cannot be performed by the nuclear industry and research alone: it requires a close partnership with end-user industries. As a first step for building such a partnership, HTR-TN proposes, together with partners of different industries (steel, chemistry...) and Technical Support Organisations of Safety Authorities a preliminary project preparing the launching of the demonstrator design, by assessing the technical, economical and safety feasibility of the coupling, proposing coupling architectures, identifying the technical and licensing issues for coupling and defining a programme of development for the reactor, the heat transport system and the industrial heat application. (authors)

[en] It is already 10 years since the (European) High Temperature Reactor Technology Network (HTR-TN) launched a program for development of HTR technology, which expanded through three successive Euratom framework programs, with many projects in line with the network strategy. Widely relying in the beginning on the legacy of the former European HTR developments (DRAGON, AVR, THTR, etc.) that it contributed to safeguard, this program led to advances in HTR/VHTR technologies and produced significant results, which can contribute to the international cooperation through Euratom involvement in the Generation IV International Forum (GIF). the main achievements of the European program, performed in complement to efforts made in several European countries and other GIF partners, are presented: they concern the validation of computer codes (reactor physics, as well as system transient analysis from normal operation to air ingress accident and fuel performance in normal and accident conditions), materials (metallic materials for vessel, direct cycle turbines and intermediate heat exchanger, graphite, etc.), component development, fuel manufacturing and irradiation behavior, and specific HTR waste management (fuel and graphite). Key experiments have been performed or are still ongoing, like irradiation of graphite and of fuel material (PYCASSO experiment), high burn-up fuel PIE, safety test and isotopic analysis, IHX mock-up thermohydraulic test in helium atmosphere, air ingress experiment for a block type core, etc. Now HTR-TN partners consider that it is time for Europe to go a step forward toward industrial demonstration. In line with the orientations of the 'Strategic Energy Technology Plan (SET-Plan)' recently issued by the European Commission that promotes a strategy for development of low-carbon energy technologies and mentions Generation IV nuclear systems as part of key technologies, HTR-TN proposes to launch a program for extending the contribution of nuclear energy to industrial process heat applications addressing (1) the development of a flexible HTR that can be coupled to many different process heat and cogeneration applications with very versatile requirements, (2) the development of coupling technologies for such coupling, (3) the possible adaptations of process heat applications required for nuclear coupling, and (4) the integration and optimization of the whole coupled system. As a preliminary step for this ambitious program, HTR-TN endeavors to create a strategic partnership between nuclear industry and R and D and process heat user industries. (authors)

[en] Good progress has been made on the Very High Temperature Reactor (VHTR) material and components investigations performed within the European Commission fifth and sixth Framework programmes. These programmes focus on the identification and investigation of key technological issues for this modular type of reactor, which offers significant advantages for the long-term development of sustainable energy and heat applications including hydrogen generation. For the fifth Framework programme two materials projects HTR-M and M1 and a component project (HTR-E) were undertaken to address requirements for the reactor pressure boundary, high temperature components (including turbine and recuperator), tribology issues and operational issues and the graphite core. For the sixth Framework programme the RAPHAEL-IP is underway addressing the remaining key issues plus extending the development and qualification to include heat exchangers, the gas circulator and design codes. The main highlights of the results from the key investigations and tests performed within these programmes are summarized. (authors)