Sander de Groot

A New Impetus for Developing Industrial Process Heat Applications of HTR in Europe

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.© 2008 ASME

High-Temperature Reactor Fuel Technology in the RAPHAEL European Project

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.Copyright

Fission-Product Behaviour During Irradiation of TRISO-Coated Particles in the HFREU1bis Experiment

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.Copyright

RAPHAEL-FT & Generation IV PYCASSO-I Irradiation

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.Copyright

Accident simulation testing in the HFR

Large numbers of fuel irradiation tests have been performed in the HFR, Petten under both normal and accident conditions. The present paper describes the accident simulation testing facilities that have been used in the past. These facilities have, amongst others, been used to perform loss of coolant accident tests and transient overpower tests. The layout of these facilities and some of the thus obtained results are described in this paper.