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To better understand whether the SiC layer can withstand the corrosion given by the chemical reaction between SiC and O2, our experiments focused mainly on the effect of oxygen on SiC-coated fuel particles at high temperature. Tests were conducted on non-irradiated coated fuel particles in an atmosphere of air over a range of temperatures between 800 and 1600°C. This paper summarizes the failure fractions, surface morphology and microstructure of the SiC coating, etc. The morphology of SiC-coated particles surfaces, optical and scanning electron micrographs and the oxygen distribution of polished SiC layers at 800, 1000 and 1200°C for 200h under air atmosphere showed that the features of SiC layers did not change in these cases. In contrast with the aforementioned cases, the behavior of SiC layers was deteriorated when the oxidation temperature was beyond 1400°C. More serious the deterioration, higher the oxidation temperature is. The thickness of SiO2 layer from outside to inside SiC layers reached 6 ∼8μm, and a large number of SiC-coated particles were broken into fragment at 1600°C. The experiment results show that the oxidation of the SiC layer proceeds slowly at temperatures around 1400°C and more rapidly as the temperature approaches 1600°C. [ABSTRACT FROM AUTHOR]

Abstract: In order to study the irradiation performance of fuel spheres for the 10MW high-temperature gas-cooled reactor (HTR-10), two in-pile irradiation tests were performed. The first irradiation test was performed in the Russian reactor IVV-2M from July 2000 to February 2003. The four irradiated fuel spheres were randomly taken from the first product batches. The central temperature of irradiated fuel spheres during this irradiation was kept between 950 and 1050°C. The maximum burnup of the irradiated spheres was 107,000MWd/tU and the maximum fast neutron fluence (E >0.1MeV) was 1.31×1025 m−2. The release-to-birth rate ratios (R/B) of Kr and Xe fission products were 10−7 to 10−5. The second irradiation test was performed in HFR Petten (HFR-EU1) from September 29, 2006 to February 19, 2010. Experiment HFR-EU1 consisted of 3 German AVR pebbles and 2 INET pebbles. The two INET pebbles were randomly taken from the latest production batch. The surface temperature of pebble INET 2 during irradiation was approx. 940°C. The experiment was performed in two campaigns from 29 September 2006 to 24 February 2008 (12 reactor cycles of 28 days) and continued from 19 October 2009 to 19 February 2010 (4 reactor cycles). Up to end of irradiation, the experiment had accumulated 16 reactor cycles totaling 445 efpd and calculated burnup and maximum fast neutron fluence (E >0.1MeV) were 9.3% (pebble INET 1) and 11.6%FIMA (pebble INET 2) and about 4.95×1025 m−2, respectively. At end of irradiation, based on 85mKr, R/B of approx. 8×10−8 was measured. The second irradiation test results are much better than the first. The irradiated sample manufacture technology and characterization, irradiation conditions and results of two irradiation tests are compared in detail in this paper. [Copyright &y& Elsevier]

Abstract: In order to evaluate if the fuel elements and their components (matrix material and coated fuel particles) can meet the design requirements of 10MW high temperature gas-cooled reactor (HTR-10), an irradiation testing with four spherical fuel elements, 60 matrix material specimens of 5mm×5mm×40mm and 13,500 coated fuel particles was performed in Russian IVV-2M reactor from July 2000 to February 2003. The irradiation temperature was 1000°C. The fast neutron fluence of matrix material specimens reached 1.3×1021 cm−2 (E >0.1MeV). Post-irradiation examination contained the visual inspection, dimension measurement and determining the density, porosity, specific electrical resistance and bending strength. The irradiation results are given in this paper, and show that the matrix material for spherical HTR-10 fuel elements made from the domestic raw materials and fabricated by the quasi-isostatic room-temperature moulding process is suitable as a structural material for spherical HTR fuel elements. [Copyright &y& Elsevier]

Abstract: An irradiation test of four spherical fuel elements (SFE) had been performed in the Russian reactor IVV-2M. The elements were sampled randomly from the first and second product batches which were manufactured for the 10MW high-temperature gas-cooled test reactor (HTR-10). The maximum burnup of the irradiated fuel elements reached 107,000MWd/tU and the maximum fast neutron fluence was 1.31×1025 m−2. The release-to-birth rate ratio (R/B) did not increase significantly during irradiation. However, an in-pile heating-up test of element SFE 7 in Capsule 5 led to a failure of approximately 6% of the coated particles. After the test it was estimated that the fuel temperature had very likely been much higher than the intended 1600°C. [Copyright &y& Elsevier]

The Chinese 10 MW high temperature gas-cooled reactor (HTR-10) attained its first criticality on December 21, 2000. The fabrication of the first fuel for the HTR-10 started in February 2000 at the Institute of Nuclear Energy Technology (INET), Tsinghua University. Up to September 2000, a total of 11 721 spherical fuel elements were successfully produced. The average free uranium fraction of the first fuel-determined by the burn-leach method-was 5.0×10−5. So far, the release rate R/B of the fission gas, measured in the irradiation test, shows that not a single particle in three irradiated spherical fuel elements failed as the results of the irradiation test carried out in Russia. This paper describes the design parameter, the fabrication technology and the performance data of the HTR-10 first fuel, and the production and quality control experiences obtained from the manufacture of the first fuel for the HTR-10. [Copyright &y& Elsevier]

The stresses in TRISO-coated fuel particles under irradiation changed with the dimensional parameters, material properties, the irradiation temperature and neutron fluence. In this paper a fuel performance model with analytic solution was used to investigate the particle stress variation and SiC tangential stress sensitivity to these variables at the irradiation early and late stages. The calculation results indicated that coating layer thickness, PyC anisotropy, density and irradiation temperature significantly affected coated fuel particles stresses under irradiation. As for the stress sensitivity analysis, more attention should be paid to SiC thickness, PyC material parameters and irradiation temperature in further model study and the manufacturing process. [ABSTRACT FROM AUTHOR]

Abstract: The improvement of the oxidation resistance of fuel element matrix graphite used in high temperature gas-cooled reactor (HTR) is indispensable for the further improvement of the safety of HTR. The stability of SiC coatings and SiC/SiO2 multilayer coatings in helium with little impurities is analyzed on the basis of thermodynamic calculation and it is found that SiC/SiO2 multilayered coatings are suitable oxidation resistant materials for graphite used in HTR fuel elements because they are stable both at the normal operation conditions and accidental conditions of HTR. SiC/SiO2 multilayer coatings were synthesized on the surface of fuel element matrix graphite of HTR by combination of vapor reaction diffusion, slurry method and high temperature oxidation in air; the oxidation behavior of SiC/SiO2 coated fuel element matrix graphite of HTR in different atmosphere are investigated and it is shown that SiC/SiO2 coatings can keep their stability under different experiment conditions which graphite used in HTR may encounter and greatly improve the oxidation resistance of fuel element matrix graphite of HTR. [Copyright &y& Elsevier]

NRG has performed a High Temperature Reactor fuel qualification test in the framework of the Chinese HTR development for INET – Tsinghua University, as a part of the qualification process of Chinese fuel for use in the HTR-PM (High Temperature Reactor-Pebble bed Module). Fuel qualification is an essential part of the licensing process of the HTR-PM, currently under construction in the Shandong province in the People’s Republic of China. The design of the INET irradiation setup for irradiation in the High Flux Reactor is performed by NRG. In the design of the irradiation rig, the pebbles are encased in graphite half shells to form a solid cylindrical stack. Within the graphite, thermocouples are located for temperature monitoring, and neutron fluence monitor sets for neutron fluence verification. Next to the temperature measurements, the online monitoring consisted of fission product release measurements. These measurements were performed with the Sweep Loop Facility, designed and built by JRC-IET. Post Irradiation Examinations are performed and consisted of gamma scanning, dimensional and weight measurements and visual inspection. In April 2016, the pebbles were transported from Petten to Karlsruhe, Germany where the second required step of fuel qualification will be performed, namely heating tests in the KÜFA facility. This paper describes the global lay-out and functionality of the irradiation facility. The online data generated and irradiation parameters are reported, with focus on the measured fission product release behavior of the fuel. The paper also presents non-destructive post irradiation examinations. [ABSTRACT FROM AUTHOR]

At the beginning, a comparative analysis was made on the oxidation corrosion rate and ash content of A3-3 matrix graphite (MG) pebbles lathed before and after high temperature purification (HTP) treatment. Their oxidation corrosion rate and ash contents were almost identical, which indicated that the HTP process was to purify the entire MG pebbles and not limited on the surfaces. Furthermore, the multiple mechanical and thermal properties of MG treated without and with the treatment of HTP at ~1900°C were compared and their microstructure features were characterized as well. As the crush strength, oxidation corrosion rate, and erosion rate of MG without HTP treatment did not satisfy the specifications, the comprehensive properties and purity of MG with HTP were improved in various degrees through the HTP process so that all performances met the requirements of the A3-3 MG. The improvement of crush strength and erosion rate of MG in the HTP process could be mainly attributed to the upgradation of ordered microstructure and corresponding increase of density. However, the enhancement of oxidation corrosion rate was due to the synergistic effects of microstructural optimization and reduction of impurity elements, especially the transition metal elements of MG in the HTP process. [ABSTRACT FROM AUTHOR]

Matrix graphite (MG) with incompletely graphitized binder used in high-temperature gas-cooled reactors (HTGRs) is commonly suspected to exhibit lower oxidation resistance in air. In order to reveal the oxidation performance, the oxidation behavior of newly developed A3-3 MG at the temperature range from 500 to 950°C in air was studied and the effect of oxidation on the compressive strength of oxidized MG specimens was characterized. Results show that temperature has a significant influence on the oxidation behavior of MG. The transition temperature between Regimes I and II is ~700°C and the activation energy (Ea) in Regime I is around 185 kJ/mol, a little lower than that of nuclear graphite, which indicates MG is more vulnerable to oxidation. Oxidation at 550°C causes more damage to compressive strength of MG than oxidation at 900°C. Comparing with the strength of pristine MG specimens, the rate of compressive strength loss is 77.3% after oxidation at 550°C and only 12.5% for oxidation at 900°C. Microstructure images of SEM and porosity measurement by Mercury Porosimetry indicate that the significant compressive strength loss of MG oxidized at 550°C may be attributed to both the uniform pore formation throughout the bulk and the preferential oxidation of the binder. [ABSTRACT FROM AUTHOR]

Online burnup measurement of a single irradiated spherical fuel element using gamma spectrometry has been applied for years on HTR-10. This reactor has a complex operation history for varies experiments, which raises the uncertainty over the non-destructive measured burnup. In this research, three irradiated spherical fuel elements with different burnup were deconsolidated, and their coated particles were analysed by both radiometric methods based on Cs-137 activity and mass spectrometric methods based on neodymium and actinide mass. The burnup distribution in each spherical fuel element was indicated by fractional U-235 burnup of particles from various radii and relatively uniform. The inventory of Cs-137 in one spherical fuel element was measured by on- and off-line gamma spectrometry and results showed tiny differences. Destructively measured Cs-137 activities from particles indicate negligible portion of Cs-137 in the graphite matrix. Burnup calculated from Cs-137 by radiometric method and Nd-148 by mass spectrometric method were compared. Results showed that the two values were not significantly different for fuels with a clear radiation history, but differences were observed in the fuel with a complex radiation history. • The burnup of irradiated HTR-10 fuel was analysed using gamma and mass spectrometry. • The burnup distribution in irradiated HTR-10 fuel was generally uniform. • Burnup of the complex radiation history spherical fuel element was re-evaluated by neodymium. [ABSTRACT FROM AUTHOR]

For High-Temperature Gas-Cooled Reactor in China, fuel particles are bonded into spherical fuel elements by a carbonaceous matrix. For the study of fuel failure mechanism from individual fuel particles, an electrochemical deconsolidation apparatus was developed in this study to separate the particles from the carbonaceous matrix by disintegrating the matrix into fine graphite powder. The deconsolidated graphite powder and free particles were characterized by elemental analysis, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and ceramography. The results showed that the morphology, size distribution, and element content of deconsolidated graphite matrix and free particles were notably affected by electric current intensity. The electrochemical deconsolidation mechanism of spherical fuel element was also discussed. [ABSTRACT FROM AUTHOR]

For the fabrication of coated particle fuel elements of high temperature gas cooled reactors, the ceramic UO 2 kernels are prepared through chemical gelation of uranyl nitrate solution droplets, which produces radioactive effluent with components of ammonia, uranium, organic compounds and ammonium nitrate. In this study, a flow sheet including evaporation, flocculation, filtration, adsorption, and reverse osmosis was established for the effluent treating. The uranium recovery could reach 99.9% after the treatment, with almost no secondary pollution produced. [ABSTRACT FROM AUTHOR]

Abstract: Zirconium carbide (ZrC) layer on pyrocarbon-coated particles was successfully prepared in a fluidized bed coater furnace by chemical vapor deposition using a zirconium chloride (ZrCl4) vapor method and quantitative controlling of the Zr-source through a ZrCl4 powder feeder. The crystal phase, microstructure and chemical composition of ZrC-coating layer were analyzed using X-ray diffraction (XRD), optical metallographical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), high-resolution transmission electron microscope (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The results show that the deposited ZrC-coating layer has smooth and compact surface, no obvious holes, clear interface with dense pyrocarbon layer, and a thickness of 35μm. The main phase of ZrC-coating layer is fcc-ZrC crystal, which is composed of small grains with the size of 20–50nm. The grain size increases monotonously with the deposition temperature increasing. The main elements of ZrC-coating layer are Zr and C, and the Zr/C molar ratio is close to 1:1. The analysis of composition and crystal structure suggest that a stoichiometric fcc-ZrC crystal was obtained and no obvious preferred orientation of the grains was found. [Copyright &y& Elsevier]

Abstract: Coated particles used in HTR fuel element sustain the inner pressure during irradiation as a pressure vessel. In actually the coated particle is not real spherical but with some asphericity, the stress distribution in the vessel is not uniform, coated layer in aspherical particle sustain more additional stress due to the asphericity. In this paper, the geometric shape distribution is summarized based on actual coated particle statistic. A mechanical analysis model is proposed for SiC layer by geometric combinations, and stress distribution of coated particle with a flat is calculated. The results show that the local maximum stress of aspherical particle increased two times than that of ideal spherical coated particle, which increase the failure probability under irradiation and high temperature. [Copyright &y& Elsevier]

Abstract: As the most promising candidate of SiC-coated fuel particles used in HTR fuel element, ZrC-coated particle has excellent irradiation performance. In this paper, ZrC coating is deposited by CVD with ZrCl4 powder supply method. ZrCl4 powder supply equipment and the saturation vapor pressure are studied, which show that saturation vapor pressure of ZrCl4 is enough to satisfy deposition of ZrC coating in fluidized bed. Several deposition parameters such as C/Zr ratio and deposition temperature are investigated theoretically and experimentally, which have influence on ZrC coating key properties, such as mol ratio of Zr/C, and density. The results show that in a given temperature, C/Zr ratio in raw gas has more influence on ZrC structure, and high quality ZrC coating can be deposited by optimal condition with this method. [Copyright &y& Elsevier]

Abstract: The HFR-EU1 irradiation in the HFR Petten was successfully conducted between 2006 and 2010 by the European Commission''s Joint Research Centre, Institute for Energy and Transport (JRC-IET). Two recently produced INET fuel pebbles and 3 historical AVR pebbles, both containing TRISO fuel particles, were irradiated at representative temperatures to burn-ups up to 14.3% FIMA, to be confirmed by measurements. The objective was to test fuel beyond the specifications of current pebble bed cores to demonstrate that HTRs are capable of enhanced sustainability (further increased power conversion efficiency, improved fuel use) and thus reduced waste production. INET and AVR pebbles were irradiated and monitored in separately controlled capsules of the same irradiation rig. Fission gas release was monitored by HP Ge gamma spectrometry thus enabling evaluation of the characteristic release over birth fraction which is indicative for the health of the fuel. In none of the pebbles, abnormally increased fission gas release was observed indicating that all of the approx. 45,000 coated particles in the pebbles had remained intact. Unexpectedly high thermocouple failure in one of the capsules had delayed the experiment because it required construction of a new safety case. This paper presents the irradiation history of the experiment including fission gas release data. [Copyright &y& Elsevier]

Abstract: Porous silicon carbide ceramics were prepared through the coat-mix method and molding, carbonization and sintering process with silicon powders and phenolic resin as raw materials. The crystalline phase, microstructure, and porosity of samples treated at different stages were characterized. Results showed that the fabricated porous silicon carbide ceramics consist of pure β-SiC phase with a homogeneous structure and porosity of above 60%. Each of the processing stages, including coat-mix, molding, carbonization, and sintering, has certain contribution to the porosity of the final porous silicon carbide ceramics, in which the mole ratio of resin carbon to silicon and the molding temperature are the main factors to affect the porosity. A porosity evolution process of porous silicon carbide ceramics during fabrication process was also proposed. [Copyright &y& Elsevier]

Abstract: Large-scale silicon carbide nanowires with the lengths up to several millimeters were synthesized by a coat-mix, moulding, carbonization, and high-temperature sintering process, using silicon powder and phenolic resin as the starting materials. Ordinary SiC nanowires, bamboo-like SiC nanowires, and spindle SiC nanochains are found in the fabricated samples. The ordinary SiC nanowire is a single-crystal SiC phase with a fringe spacing of 0.252nm along the [111] growth direction. Both of the bamboo-like SiC nanowires and spindle SiC nanochains exhibit uniform periodic structures. The bamboo-like SiC nanowires consist of amorphous stem and single-crystal knots, while the spindle SiC nanochains consist of uniform spindles which grow uniformly on the entire nanowires. [Copyright &y& Elsevier]

Abstract: High specific surface area porous SiC ceramics, coated completely with reticulated amorphous SiC nanowires, have been fabricated with commercially available phenolic resin and silicon powders using a novel method. The results indicate that the specific surface area and porosity of the as-synthesized materials can be up to 112m2 g−1 and 81%, respectively. The coated amorphous SiC nanowires have uniform structure and smooth surfaces. The electron emission turn-on field and threshold field are about 2.9 and 6.7Vμm−1, respectively. This kind of materials may simultaneously possess the unique properties of porous materials, SiC, and nanowires. And they may have promising applications in a wide variety of areas. [Copyright &y& Elsevier]

Abstract: A novel three-step process is used to fabricate submicron silicon carbide powders in this paper. The commercially available silicon powders and phenolic resin are used as raw materials. In the first step, precursor powders are produced by coating each silicon powder with phenolic resin shell. Then, precursor powders are converted into carbonized powders by decomposing the phenolic resin shell. The submicron silicon carbide powders are formed in the reaction of silicon with carbon during the third step of thermal treatment. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and thermogravimetric (TG) analyses are employed to characterize the microstructure, phase composition and free carbon content. It is found that the sintered powders consist of β-SiC with less than 0.2 wt.% of free carbon. The particle size of the obtained silicon carbide powders varies from 0.1 to 0.4 μm and the mean particle size is 0.2 μm. The silicon carbide formation mechanism of this method is based on the liquid–solid reaction between liquid silicon and carbon derived from phenolic resin. The heat generated during the reaction leads to great thermal stress in silicon carbide shell, which plays an important role in its fragmenting into submicron powders. [Copyright &y& Elsevier]

Abstract: The R&D of spherical fuel elements for the 10MW high temperature gas-cooled reactor (HTR-10) started in 1986 in China. A process known as cold quasi-isostatic molding was used for manufacturing spherical fuel elements, and about 20,540 spherical fuel elements were produced in 2000 and 2001. Fabrication technology and graphite matrix materials were investigated and optimized. Cold properties of the spherical fuel elements met the design specifications. The mean free uranium fraction of 44 batches was 4.57×10−5. In-pile irradiation test results showed that irradiation did not lead to apparent change in linear dimensional, geometrical density, porosity and strength of matrix graphite samples. No cracks and blisters were observed in spherical fuel elements. This indicated that matrix graphite and spherical fuel elements of HTR-10 met the requirement of design specifications. [Copyright &y& Elsevier]

A new antistatic fiber was investigated by using carbon nanotubes (CNTs) to improve the antistatic ability of inner antistatic agents, which bases on the mechanism of attracting moisture by polar radical groups. Composite antistatic agents, prepared by dispersing CNTs in organic antistatic agent, were cospun with polypropylene to prepare antistatic fibers with an inner structure of “sea-island”. The analysis of the measured tribo-electrostatic charges indicated that the antistatic ability of the fibers filled with composite antistatic agent was superior to that of the fibers filled with pure organic antistatic agent. It was also indicated that the antistatic effect promoted by adding CNTs was better than by adding conductive carbon black. The further study showed that antistatic effects promoted by CNTs were enhanced as the diameters and the curvatures of CNT walls were lessened. Moreover, the antistatic effects promoted by the high temperature treated CNTs were also discussed. [Copyright &y& Elsevier]

Abstract: The density of porous pyrocarbon layer of coated fuel particles is one of the important parameters of the coated fuel particles. It directly affects the performance of fuel elements. A measurement method, particle size analyzer method, to analyze the density of porous pyrocarbon was developed, and the standard uncertainty of this method was analyzed. Results showed that the particle size analyzer method has the advantages of fast measurement, large sampling number and high measurement accuracy. This method is very efficient for engineering application and is a promising candidate method to measure the density of porous pyrocarbon of coated fuel particles. [Copyright &y& Elsevier]

Abstract: Coat mix process is employed to synthesize high purity porous SiC ceramics with phenolic resin and silicon powders as starting materials. The results show that the fabricated porous SiC ceramics have a homogeneous structure with interconnected open pores and dense struts. They also have a relatively narrow pore size distribution in the range of 1–6μm. The total porosity and the average pore size are 62% and 2.6μm, respectively. [Copyright &y& Elsevier]

• 7 INET HTR fuel elements irradiated in HFR Petten were sent to Karlsruhe for PIE. • The burn-up of these fuel elements was determined via gamma spectroscopy. • D-LOFC incidents were simulated in the KÜFA device in the JRC Hot Cells up to 1770°C. • Typical releases of Cs after the first test phase at 1620 °C were less than 2.5·10−5. • The release of Kr-85 was below the detection limits during the first heating phases. The current paper reports the results of gamma spectroscopic burn-up determination and KüFA safety testing at JRC Karlsruhe on spherical high-temperature reactor fuel elements, which were fabricated by the Institute of Nuclear and New Energy Technology of the Tsinghua University, Beijing. The fuel elements were irradiated in the High Flux Reactor, Petten, in the frame of the HFR-EU1 and HTR-PM campaigns and transported to JRC Karlsruhe for post-irradiation examination and accident testing in the KüFA device in the frame of a bilateral safety research study. Burn-up determination was performed on seven fuel elements based on the quantitative measurement of their Cs-137 inventories using an established gamma spectroscopy set-up in the JRC hot cell facilities. Accident testing was conducted on three HTR-PM fuel elements in several phases at simulated accident temperatures between 1620 °C and 1770 °C for 150 h to simulate hypothetical depressurization and loss-of-forced circulation accidents. The release of Kr-85 was measured during the tests in a cold trap and solid fission product release was determined by gamma spectroscopic analyses of exchangeable cold plates in a low background environment. After successful completion of the KüFA tests the fuel elements are currently undergoing further post-irradiation examinations including profile disintegration as well as ceramography and scanning electron microscopy of individual coated particles. [ABSTRACT FROM AUTHOR]

Porous titanium carbide ceramics are fabricated by the coat-mix process with phenolic resin as the carbon source, and titania powders as the titanium source. The phase composition, residual free carbon content, and microstructure have been investigated by X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy, respectively. The results indicate that phase-pure titanium carbide materials can be obtained using this process. A large number of pores exist in the fabricated titanium carbide ceramics. [Copyright &y& Elsevier]