Latest achievements of CEA and AREVA NP on HTR fuel fabrication

International audienceExtensive research and development programs on the (Very) High Temperature gas cooled Reactor (V/HTR) are being conducted by many countries mainly promoted by the attractiveness of this concept and its capability for other applications than electricity production, such as high temperature process heat and cogeneration. In this international context, the Commissariat à l'Energie Atomique (CEA) and AREVA NP through its project called ANTARES (Areva New Technology for Advanced Reactor Energy Supply) conduct a V/HTR fuel development and qualification program, among which one major activity is dedicated to the mastering of the nuclear fuel fabrication technology. The fuel concept selected for this project is the compact design based on UO2 kernels and SiC coating. First laboratory-scale experiments were performed to recover the know-how of HTR-coated particles and fuel element manufacturing. The different stages of UO2 kernel fabrication by the Gel Supported Precipitation (GSP) process were reviewed and improved. Experimental conditions for the Chemical Vapour Deposition (CVD) of coatings have been defined on dummy kernels supported by a modelling approach of the CVD process. The compacting processes formerly used at CERCA were reviewed and updated. In order to support a future industrial manufacturing factory and to meet the next short-term challenge, which is the fabrication of coated particle batches that will be compacted for the first irradiation test scheduled in OSIRIS, a lab-scale experimental manufacturing facility, named CAPRI (CEA and AREVA PRoduction Integrated) line has been set up and is in operation since early 2005. The CAPRI line is composed of a manufacturing line for TRISO particles, named GAIA, located at CEA Cadarache, and a compacting line for fuel elements based at CERCA, AREVA NP Subsidiary, Romans. Since early 2005, many tests have been performed leading to a better understanding and optimization of coating particle and compact manufacturing processes. In support to this fuel fabrication tool, development of accurate characterization methods were carried out to supply products meeting the specifications and to provide feed-back information to enhance fuel production quality

Interdiffusion behaviors in doped molybdenum uranium and aluminum or aluminum silicon dispersion fuels: Effects of the microstructure

International audienceSi addition to Al is considered as a promising route to reduce (U,Mo)-Al interaction kinetics, due to its accumulation in the interaction layer, yielding the formation of silicide phases. The (U,Mo) alloy microstructure, and especially its homogenization state, could play a role on this accumulation process. The addition of a third element in γ(U,Mo) could also influence diffusion mechanisms of Al and Si. These two parameters were studied by means of diffusion couple experiments by joining γU based alloys with Al and (Al,Si) alloy. Chemical elements X added into γ(U,Mo) were thoroughly chosen on the following criteria: (i) the potential solubility of the alloying element into the γ(U,Mo) matrix, (ii) its capability to form the ternary aluminides based on the CeCr2Al20 and Ho6Mo4Al43 - types, and (iii) the feasibility to control the microstructure of the alloys. On this basis, a test matrix is defined. It concerns γ(U80,Mo15,X5) alloys (in at.%) with X = Y, Cu, Zr, Ti or Cr. These alloys were homogenized and coupled with Al or (Al,Si) alloy. Results evidenced, first, the importance of the state of homogenization of the γ(U,Mo) binary alloy on interaction processes with (Al,Si) alloy, and the benefit on the diffusion of Si through the interaction layer, as observed on the elementary concentration profiles, when the third element X has some solubility into γ(U,Mo) alloy

High-Temperature Reactor Fuel Technology in the European Projects HTR-F1 and RAPHAEL

In April 2005, a new 4-year Integrated Project on Very High Temperature Reactors (RAPHAEL: ReActor for Process Heat And ELectricity) was started as part of EURATOM’s 6th Framework Programme. The Sub-Project on Fuel Technology (SP-FT) is one of eight sub-projects in RAPHAEL, with 8 partners from industry, R&D organizations and a nuclear-safety expertise organization: CEA, FZ Jülich, JRC, Nexia Solutions, AREVA-NP, NRG, Belgonucléaire and IRSN. While the earlier HTR-F and HTR-F1 projects aimed at re-mastering fuel fabrication technology, testing existing state-of-the-art HTR fuels at high burn-up and high temperature and understanding fuel behavior), the R&D conducted in RAPHAEL SP-FT focuses on understanding fuel behavior and determining the limits of state-of-the-art fuel as well as on potential further Fabrication processes will be developed for an alternative kernel composition (UCO), with a potential for decreasing the CO pressure built-up in the particle, and for an alternative coating layer (ZrC), which remains more stable at higher temperature than SiC, thus providing increased Post-irradiation examinations and heat-up tests performed on irradiated fuel will allow investigation of the behavior of state-of-the-art fuel in a VHTR’s normal and accidental conditions. Based on the fuel particle models established in FP5, the fuel modeling capabilities will be improved: An irradiation will be performed in the HFR Petten for measuring the changes in coating material properties as a function of fluence and temperature, with samples coming from the new fabrication process. This will allow introduction of particle behavior models for coatings which are not only more accurate than those presently based on old data, but also more relevant to present materials. Fission-product release modeling and statistical methods will be developed to integrate the individual behavior of thousands of particles within fuel elements. Code benchmarking, started in FP5, will be continued with the acquisition of new experimental data. This paper presents progress in RAPHAEL SP-FT as well as the remaining activities of the earlier HTR-F1 project.JRC.F.3-High Flux and Future Reactor

SAIGA : an in-pile test largely instrumented and devoted to study the degradation of a Sodium Fast Reactor core with mitigation device in Severe Accident Conditions

International audienceAfter the end of ASTRID conceptual design studies, CEA has launched a long-term R&D roadmap on generic Sodium Fast Reactor issues including the Severe Accident field based on 3 pillars:- Improving knowledge of the phenomena and equations governing the sequence of events occurring during a severe accident. Developing existing or future calculation codes and numerical platforms focusing specifically on severe accidents in order to sequence and couple these codes;- Extend the experimental database needed to validate the calculation and simulation tools, such as SIMMER-V code, to cover the ranges of the parameters expected in future reactors incorporating advanced design options;- Qualify innovative systems for mitigating the consequences of radioactive emissions in severe accident conditions proposed for future reactors.Transfer Tubes have been installed in recent SFR core designs so that molten core can rapidly relocate out of core region. The objective is to prevent prompt criticality in the core region by removing sufficiently rapidly a significant mass of fissile material. This mitigation device is designed to help return the reactor to a safe state after a severe accident. SAIGA Project will provide experimental results of an integral test to validate SIMMER-V calculations on Corium Transfer Tube

High Temperature Reactor Fuel Technology in 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 fuelsimulation code. The PYCASSO irradiation experiment is a true Generation IV VHTR effort, with Korean and Japanese samples included in the irradiation1. 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 HFREU1bis pebbles were obtained, showing a clear temperature (and high burn-up) influence on both kernel changes (including fission product behaviour) and the coating layers2. 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.JRC.F.3-Energy securit

Thermal conductivity measurement of IRIS-TUM fuel plates (disperse U-8wt.%-Mo)

The thermal diffusivity of ground U-8wt.%-Mo powder in an aluminium matrix has been measured in the temperature range of 300°C to 400°C. By means of best estimates for the heat capacity and density of this complex compound a thermal conductivity of about 25 W/mK has been determined.JRC.E.3-Materials researc

Achievements of recent research on severe accidents at CEA/IRESNE in support of future nuclear fission technology

International audienceIn the current context of nuclear revival under the constraint of global warming and an ever-increasing world demand for energy, it is essential to take all precautions in the event of a serious accident during the design phase and to review the severe accident mitigation features of existing plants. The current nuclear revival is accompanied by the development of prototypes based on alternative concepts to light water reactors, such as the Sodium-cooled Fast Reactor (SFR), High Temperature Reactor (HTR), Molten Salt Reactor (MSR), which are also under consideration as reactors of reduced power output, or Small Modular Reactors (SMR). This paper summarizes the main outcomes and achievements of the last five years of experimental and numerical research conducted at CEA/IRESNE into prospective severe accidents within Pressurized Water Reactors (PWR) and SFRs

De novo variants in TCF7L2 are associated with a syndromic neurodevelopmental disorder

TCF7L2 encodes transcription factor 7-like 2 (OMIM 602228), a key mediator of the evolutionary conserved canonical Wnt signaling pathway. Although several large-scale sequencing studies have implicated TCF7L2 in intellectual disability and autism, both the genetic mechanism and clinical phenotype have remained incompletely characterized. We present here a comprehensive genetic and phenotypic description of 11 individuals who have been identified to carry de novo variants in TCF7L2, both truncating and missense. Missense variation is clustered in or near a high mobility group box domain, involving this region in these variants' pathogenicity. All affected individuals present with developmental delays in childhood, but most ultimately achieved normal intelligence or had only mild intellectual disability. Myopia was present in approximately half of the individuals, and some individuals also possessed dysmorphic craniofacial features, orthopedic abnormalities, or neuropsychiatric comorbidities including autism and attention-deficit/hyperactivity disorder (ADHD). We thus present an initial clinical and genotypic spectrum associated with variation in TCF7L2, which will be important in informing both medical management and future research