This paper first provides an update on the current state of play and the potential future role of nuclear energy in Europe. It then describes the EU energy policy tools in the area of nuclear technology. It explains the three-tier strategy of the European nuclear technology platform and its demonstration initiatives, here specifically for nuclear cogeneration and HTR. The paper closes with an outlook on the boundary conditions at which HTR can become attractive for nuclear cogeneration, not only from an energy policy viewpoint but also economically.

The purpose of this paper is to provide an update on the international effort in the development of the Very High Temperature Reactor system pursued through international collaboration in the Generation IV International Forum (GIF) and an outlook for further activities.The initial motivations to develop this reactor type are recalled, a historical overview is given about technology developments and test reactors since 1945 and several of the targeted non-electric applications of VHTR power are addressed.Cooperation in the frame of GIF is clearly beneficial for all project partners. Initially, a wealth of historical experience was collected and shared in the form of documents, dedicated workshops or fuel and material samples. This exchange included properties data, fabrication, irradiation and post-irradiation testing methods, quality assurance, design and analysis tools and methods, as well as the experience in building and operating related equipment. In the further course of the project execution, time, effort and scarce facilities (such as irradiation space or hot cell equipment) are shared, they accelerate progress and create synergies.Recent highlights from currently active GIF VHTR R&D projects (Materials, Fuel and Fuel Cycle, Hydrogen Production) are then provided and placed into the context of the GIF VHTR signatories' national programs. The majority of these currently focus on licensing requirements for demonstrators of near term process steam production scenarios while more aggressive, longer term and higher temperature applications are mainly pursued to enable thermochemical production of bulk hydrogen.Based on the VHTR's high technology readiness level, orientations for future R&D are outlined which would contribute to enhancing the system's market readiness level. These include work on System Integration and Assessment, Safety Analysis and Demonstration, Waste Minimization and Cost Reductions.The inherent safety characteristics of the VHTR are a precious asset for it to become a strong response to today's concerns of nuclear safety, energy security and climate change. (C) 2014 Published by Elsevier Ltd.

Ten years ago, the European High Temperature Reactor (HTR) Technology Network (HTR-TN) launched a programme for developing HTR Technology, which expanded so far through 4 successive Euratom Framework Programmes. Many projects have been performed - in particular the RAPHAEL project in the 6th Euratom Framework Programme and presently ARCHER in the 7th - in line with the Network strategy that identified cogeneration of process heat and power as the main specific mission of HTR. HTR can indeed address the growing energy needs of industry presently fully relying on fossil fuel combustion with a CO(2)-lean generation technology, thanks to its high operating temperature and to its unique flexibility obtained from its large thermal inertia and its low power.Relying on the legacy of the former European leadership in HTR technology, this programme has addressed specific developments required for industrial process heat applications and for increasing HTR performances (higher temperatures and fuel burn-up). Decisive achievements have been obtained concerning fuel manufacturing and irradiation behaviour, key components and their materials, safety, computer code validation and specific HTR waste (fuel and graphite) management. Key experiments have been performed or are still ongoing: irradiation of graphite, fuel and vessel materials and the corresponding post-irradiation examinations, safety tests and isotopic analyses; thermal-hydraulic tests of an Intermediate Heat Exchanger mock-up in helium; air ingress experiments for a block type core, etc. Through Euratom participation in the Generation IV International Forum (GIF), these achievements contribute to international cooperation.HTR-TN strategy has been recently integrated by the "Sustainable Nuclear Energy Technology Platform" (SNE-TP) as one of the 3 "pillars" of its global nuclear strategy. It is also in line with the orientations and the timing of the "Strategic Energy Technology Plan (SET-Plan)" for the development of CO(2)-lean energy technologies, and thus strengthens the nuclear option in a future European energy mix.Nuclear cogeneration for industrial process heat applications is a major innovation and a major challenge, requiring large-scale demonstration to prove its industrial viability. To enable demonstration, it is necessary not only to develop an appropriate nuclear heat source, but also to develop coupling technologies and to adapt industrial processes to the coupling with a HTR This requires a close partnership between the conventional and the nuclear technology holders as the base of a Nuclear Cogeneration Industrial Initiative.Recently the project EUROPAIRS initiated by HTR-TN together with process heat user industries has set the bases of such a strategic partnership. (C) 2011 Elsevier B.V. All rights reserved.

Since the late 1990s several large scale modeling programs have been initiated, especially in Europe and in the USA, to address the most important safety and economics related material problems that affect nuclear power plant (NPP) components around the world. Some programs were in support of the design of components for future nuclear fission and fusion systems. These programs aimed at combining different computer simulation tools, each dealing with different time and length scales, to develop platforms of integrated codes that, in a multi-scale modeling framework, would allow nuclear materials degradation processes to be studied in silico. These platforms of codes could eventually be used to describe and anticipate the behavior of materials in operation, allowing failure to be timely foreseen and thus possibly avoided through mitigation strategies. They could also contribute to improve materials performance, optimize component design and better plan a reduced number of neutron irradiation experiments. This article overviews the most notable large scale programs of this type in Europe, briefly describing their focus, objectives and main outcomes. In the conclusions some considerations on current and future needs and trends in connection with large scale modeling programs are made.

The "analytical" PYCASSO (PYrocarbon irradiation for Creep and Swelling/Shrinkage of Objects) irradiations focus on determining the effects of neutron irradiation in the temperature range of 900-1100 degrees C, excluding effects due to the presence of fuel, such as pressurization or chemical attack by fission products. These irradiations can therefore be considered separate effect tests, where only the influence of neutron fluence and temperature on coatings and coating combinations is investigated.For this purpose dedicated particles have been manufactured consisting of surrogate kernels (ZrO(2) and Al(2)O(3)) with different types of PyC/SiC/ZrC coatings and coating combinations. All specimens delivered have been extensively characterized, such that even potentially small changes due to the irradiation in dimensions, microstructure and density can be determined accurately after irradiation.Partners involved in this irradiation are CEA (France), JAEA (Japan) and KAERI (South Korea). The PYCASSO irradiations take place in the High Flux Reactor (HFR) in Petten, and are coordinated by NRG (The Netherlands). The partnership for PYCASSO was initiated by the RAPHAEL (V)HTR European 6th Framework Program and is integrated in the Generation IV International Forum VHTR Fuel and Fuel Cycle project. (C) 2010 Elsevier B.V. All rights reserved.

The irradiation experiment HFR-EU1bis, coordinated by the European Joint Research Centre – Institute for Energy, was performed in the High Flux Reator (HFR) at Petten to test five spherical HTR fuel pebbles of former German production with TRISO coated particles in conditions beyond the specifications of current HTR reactor designs (central temperature of 1250°C). In this paper, the behaviour of the fission products (FPs) and kernel micro-structure evolution during the test are investigated. While FP behaviour is a key issue for potential source term evaluation it also determines the evolution of the oxygen potential in the oxide kernel which in turn is important for formation of carbon oxides (amoeba effect and pressurization). Fission-gas release from the kernel can induce additional mechanical loading and finally some FPs (Ag, Cs, Sr) might alter the mechanical integrity of the coatings. This study is based on postirradiation examinations (ceramography + EPMA) performed both on UO2 kernels and on coatings. Significant evolutions of the kernel as a function of temperature are shown (grain structure, porosity, size of metallic inclusions). The quality of the ceramography results allows characteristics of the intergranular bubbles in the kernel (and estimation of swelling) to be determined. Remarkable results considering FP release from the kernel have been observed and will be presented. Examples are the significant release of Cs out of the kernel as well as Pd, whereas Zr remains trapped. Mo and Ru are mainly incorporated in metallic precipitates. These observations are interpreted and mechanisms for FP and micro-structural evolutions are proposed. These results are coupled to the results of calculations performed with the mechanistic code MFPR (Module for Fission Product Release) and the thermodynamic database MEPHISTA (Multiphase Equilibria in Fuels via Standard Thermodynamic Analysis). The effect of high flux rate and high temperature on fission gas behaviour, grain size evolution and kernel swelling are discussed. In addition, solid-FP behaviour (Cs, Mo, Zr, Ba, Sr) is discussed in connection with the evolution of kernel oxygen potential and evolution of the pressure of carbon oxides. The paper intends to be exemplary on how the combination of post-irradiation examination results and fuel modelling increases fundamentally the understanding of HTR fuel behaviour.

This paper describes selected equipment and expertise on fuel irradiation testing at the High Flux Reactor (HFR) in Petten, The Netherlands. The reactor went critical in 1961 and holds an operating license up to at least 2015. While HFR has initially focused on Light Water Reactor fuel and materials, it also played a decisive role since the 1970s in the German High Temperature Reactor (HTR) development program. A variety of tests related to fast reactor development in Europe were carried out for next generation fuel and materials, in particular for Very High Temperature Reactor (V/HTR) fuel, fuel for closed fuel cycles (U–Pu and Th–U fuel cycle) and transmutation, as well as for other innovative fuel types. The HFR constitutes a significant European infrastructure tool for the development of next generation reactors. Experimental facilities addressed include V/HTR fuel tests, a coated particle irradiation rig, and tests on fast reactor, transmutation and thorium fuel. The rationales for these tests are given, results are provided and further work is outlined.

Due to its high operating temperature (up to 850°C with present technologies, possibly higher in the longer term), and its power range (a few hundred MW), the modular HTR could address a larger scope of industrial process heat needs than other present nuclear systems. Even if HTR can contribute to competitive electricity generation, this potential for industrial heat applications is the main incentive for developing this type of reactor, as it could open to nuclear energy a large non-electricity market. However several issues must be addressed and solved successfully for HTR to actually enter the market of industrial process heat: 1) as an absolute prerequisite, to develop a strategic alliance of nuclear industry and R&D with process heat user industries. 2) to solve some key technical issues, as for instance the design of a reactor and of a coupling system flexible enough to reconcile a single reactor design with multiple applications and versatile requirements for the heat source, and the development of special adaptations of the application processes or even of new processes to fit with the assets and constraints of HTR heat supply, 3) to solve critical industrial issues such as economic competitiveness, availability and 4) to address the licensing issues raised by the conjunction of nuclear and industrial risks. In line with IAEA initiatives for supporting non-electric applications of nuclear energy and with the orientations of the SET-Plan of the European Commission, the (European) HTR Technology Network (HTR-TN) proposes a new project, together with industrial process heat user partners, to provide a first impetus to the strategic alliance between nuclear and non-nuclear industries. End user requirements will be expressed systematically on the basis of inputs from industrial partners on various types of process heat applications. These requirements will be confronted with the capabilities of the HTR heat source, in order to point out possible discrepancies and issues, to assess the feasibility of different coupling schemes and to identify development needs. Partners from nuclear regulatory organisations will also address the feasibility of licensing such coupling schemes. The issues they will raise will be taken into consideration for defining coupling design bases and identifying R&D needs. A detailed roadmap for designing an industrial demonstrator of a HTR coupled with process heat applications will be inferred from this analysis, as well as R&D actions required for supporting the development of the reactor, of the coupling system and of possible adaptations or innovations in industrial processes.

Within the Raphael (V)HTR 6th framework EU-program, the PYCASSO experiments have been devised to investigate coating behaviour under irradiation. Samples have been included from CEA (France), JAEA (Japan) and KAERI (Republic of Korea), which makes this irradiation a real Generation IV effort. The experiment is a separate effect test, where the influence of fuel (coating corrosion or micro structural change due to fission products), thermal gradients, and variation in coating microstructure and dimensions have been minimized by the use of dummy kernels (Al2O3 and ZrO2), high conductivity particle holder material combined with low energy production of the kernels, and strict (fabrication) quality control and selection procedures respectively. The purpose of the experiment is threefold for the partners involved: - for CEA to determine the behaviour of pyrocarbon under irradiation, especially the interaction of pyrocarbon swelling and creep with SiC coating layers. The results will be used to validate and improve HTR fuel performance modelling. - for JAEA to investigate the behaviour of ZrC coatings, which have been successfully manufactured, but require post-irradiation investigation and characterization. - for KAERI to determine the influence of fabrication of pyrocarbon layers with different densities on the behaviour under irradiation. The paper will go into more detail on the goals to be achieved by the different partners. The PYCASSO-I irradiation is performed in the High Flux Reactor (HFR) in Petten, The Netherlands. The experiment accommodates temperature regions of 900, 1000 and 1100°C, and contains 76 separate particle sample holders. The PYCASSO-I irradiation is a completely new design and will be described in detail, including the route from the concept definition via feasibility studies, fabrication and assembly, up to the irradiation, which took only 1, 5 year. At the time of the conference, the PYCASSO-I irradiation will be finished and a full evaluation of the irradiation will be presented. Additionally, the future post irradiation examination planned for the PYCASSO-I samples and the details of the PYCASSO-II irradiation will be outlined.

Within the scope of the 5th EURATOM Framework Programme (FP) for the HTR-F and HTR-F1 projects, a new 4-year integrated project on very high temperature reactors (RAPHAEL: ReActor for Process Heat And Electricity) was started in April 2006 as part of the 6th Framework Programme. The Sub-Project on Fuel Technology (SP-FT) is one of eight sub-projects constituting the RAPHAEL project. R&D conducted in this sub-project focuses on understanding fuel behaviour, determining the limits of state-of-the-art fuel, and developing potential performance improvements. Fabrication processes were worked out for alternative fuel kernel composition (UCO instead of UO2) and coating (ZrC instead of SiC): i) UCO microstructure reduces fission product migration and is thus considered superior to UO2 under high burn-ups and high temperature gradients. For this reason, the manufacturing feasibility of UCO kernels using modified external sol-gel routes was addressed. The calcining and sintering steps were particularly studied. ii) For its better high temperature performance, ZrC is a candidate coating material for replacing SiC in TRISO (TRistructural ISOtropic) particles. One of the objectives was therefore to deposit a stoichiometric ZrC layer without impurities. An “analytical irradiation” experiment currently performed in the HFR — named PYCASSO for PYrocarbon irradiation for Creep And Swelling/Shrinkage of Objects — was set up to measure the changes in coating material properties as a function of neutron fluence, with samples coming from the new fabrication process. This experiment was started in April 2008 and will provide data on particle component behaviour under irradiation. This data is required to upgrade material models implemented in the ATLAS fuel simulation code. The PYCASSO irradiation experiment is a true Generation IV VHTR effort, with Korean and Japanese samples included in the irradiation. Further RAPHAEL results will be made available to the GIF VHTR Fuel and Fuel Cycle project partners in the future. Post-irradiation examinations and heat-up tests performed on fuel irradiated in an earlier project are being performed to investigate the behaviour of state-of-the-art fuel in VHTR normal and accident conditions. Very interesting results from destructive examinations performed on the HFR-EU1bis pebbles were obtained, showing a clear temperature (and high burn-up) influence on both kernel changes (including fission product behaviour) and the coating layers. Based on fuel particle models established earlier, the fuel modelling capabilities could be further improved: i) Modelling of fuel elements containing thousands of particles is expected to enable a statistical approach to mechanical particle behaviour and fission product release. ii) A database on historical and new fuel properties was built to enable validation of models. This paper reports on recent progress and main results of the RAPHAEL sub-project on fuel technology.

The irradiation experiment HFR-EU1bis was performed by the European Commission's Joint Research Centre-Institute for Energy (JRC-IE) in the HFR Petten to test five spherical High Temperature Reactor (HTR) fuel pebbles of former German production with TRISO coated particles for their potential for very high temperature performance and high burn-up. The irradiation started on 9 September 2004 and was terminated on 18 October 2005 after 10 reactor cycles totaling 249 efpd and a maximum burn-up of 11.07% FIMA.The objective of the HFR-EU1bis test was to irradiate five HTR fuel pebbles at conditions beyond the characteristics of current HTR reactor designs with pebble bed cores, e.g. HTR-Modul, HTR-10 and PMBR. This should demonstrate that pebble bed HTRs are capable of enhanced performance in terms of sustainability (further increased power conversion efficiency, better use of fuel) and thus reduced waste production. The central temperature of all pebbles was kept as closely as possible at 1250 degrees C and held constant during the entire irradiation, with the exception of HFR downtime and power transients. This is the expected maximum central fuel temperature of a pebble bed VHTR with a coolant outlet temperature of 1000 degrees C.HFR-EU1bis should demonstrate the feasibility of low coated particle failure fractions under normal operating conditions and more specifically:increased central fuel temperature of 1250 degrees C compared to 1000-1200 C in earlier irradiation tests;irradiation to a burn-up close to 16% FIMA, which is double the license limit of the HTR-Modul; due to a neutronics data processing error, the experiment was prematurely terminated at 11.07% FIMA maximum so that this objective was not fully achieved;confirmation of low coated particle failure fractions due to temperature, burn-up and neutron fluence.This paper provides the irradiation history of the experiment including data on fission gas release. Postirradiation examinations at NRG Petten and JRC-ITU Karlsruhe included the verification of the received neutron fluences, burn-up and spectrum. They will be followed shortly by safety-relevant heating tests at JRC-ITU to verify fission product retention by out-of-pile heating tests beyond 1600 C. (C) 2008 Michael A. Futterer. Published by Elsevier B.V. All rights reserved.

The irradiation experiment HFR-EU1bis aims at testing 5 spherical High Temperature Reactor (HTR) fuel pebbles with TRISO coated particles for their potential for very high temperature performance and high burn up. The irradiation will start on 10 September 2004 in the HFR Petten for up to 350 fpd. The main objective of HFR-EU1bis is the demonstration of the feasibility of low particle failure rates at very high temperature (relevance for the Generation IV concept VHTR) and burn-up for the existing German LEU-TRISO fuel. The design of HFR-EU1bis is based on previous experience of HTR fuel irradiations within the European Union (1). In the rig, the pebbles are double contained and their temperature is controlled by adjusting He/Ne mixtures in the gas gaps. The two containments remain normally closed with stagnant gas mixtures. They can be purged to modify the gas mixtures for temperature adjustment and for taking gas samples to monitor release of gaseous fission products. To accelerate the burn-up, the neutron spectrum is strongly moderated using a custom filler element with increased water fraction. Cycle-by-cycle turning of the experiment by 180º reduces radial gradients in neutron fluence and burn-up across the pebbles. A vertical displacement unit (VDU) enables an optimized position of the fuel pebbles with evolving neutron flux buckling of the reactor. This paper describes the irradiation facility and its ancillary equipment. First irradiation results will be presented orally during the HTR 2004 conference.