Oxidation of titanium beryllide fabricated by plasma-sintering method

It is imperative to establish the blanket technologies for realization of D-T fusion reactors. The neutron multiplier in the fusion reactor blankets plays one of the key roles with regard to breeding of tritium. Metallic beryllium has been considered as a primary candidate for the neutron multiplier, but it is highly reactive with water vapor and oxygen at high temperatures producing H₂ and BeO. Thus, it is necessary to develop more advanced neutron multipliers that are more chemically stable than metallic beryllium. One of the intermetallic compounds of beryllium and titanium, Be₁₂Ti, possesses high tolerance to water vapor and oxygen, low swelling property, and better compatibility with structural materials. Thus, it could be an alternative of metallic beryllium. However, few experimental data are available for this material, and thus more experimental studies need to be performed to evaluate its performance as a neutron multiplier. In this study, a Be₁₂Ti sample was fabricated by a new production route, plasma-sintering method, and of which reactivity with O₂ and H₂O was examined. Experimental results suggest that the Be₁₂Ti sample prepared by the new production route possesses high resistance to oxidation by O₂ and H₂O.     

X-ray study of surface layers of air-annealed Be12Ti and Be12V samples using synchrotron radiation

Titanium beryllide Be₁₂Ti and vanadium beryllide Be₁₂V are considered to be promising materials for advanced neutron multipliers in the helium-cooled breeding blanket of DEMO reactor. A study of the surface layers of oxidized beryllide specimens by means of powder X-ray diffraction technique is presented in this work. The phase composition of the near-to-surface layers of Be₁₂Ti and Be₁₂V specimens was investigated at the Single Crystal Diffraction (SCD) beamline at ANKA synchrotron facility after air-annealing at 800 °C. A high surface sensitivity of measurements was achieved at grazing incidence conditions by varying the incidence angle. Since beryllium has low values of X-ray absorption, the near-surface regions having depths from 2 up to 20 μm were investigated. The main objective of the work is the evaluation of composition of the reactant products which can influence the parameters of retention and release of radiogenic gases.     

Novel granulation process of beryllide as advanced neutron multipliers

Advanced neutron multipliers with low swelling and high stability at high temperatures are desired for pebble bed blankets of demonstration fusion power (DEMO) reactors. Beryllium intermetallic compounds (beryllides) are the most promising advanced neutron multipliers. In order to fabricate the beryllide pebbles, beryllide with shapes of block and/or rod is necessary when a melting granulation process is applied such as a rotating electrode method. A plasma sintering method has been proposed as new technique which uses a non conventional consolidation process. It was clarified that the beryllide could be simultaneously synthesized and jointed by the plasma sintering method in the insert material region between two beryllide blocks. Beryllide rod of Be₁₂Ti with 10 mm in diameter and 60 mm in length has been successfully fabricated by the plasma sintering method. Using this plasma-sintered beryllide rod, fabrication of prototype beryllide pebble was performed by a rotating electrode method as one of the melting methods. The prototype pebbles of Be₁₂Ti with 1 mm in average diameter were successfully fabricated.     

Characterisation of titanium beryllides with different microstructure

Preliminary investigations revealed that beryllides like Be₁₂Ti may be much more suitable for use as a neutron multiplier in future fusion power plants compared to pure beryllium. Two sorts of Be–Ti samples having different grain sizes but consisting, mainly, of Be₁₂Ti have been fabricated. Investigation of microstructure and measurements of tritium release rate allow make a comparison between both types of fabricated titanium beryllides. Obtained results are disclosed in this paper.     

Fabrication of beryllide pebble as advanced neutron multiplier

Fusion reactors require advanced neutron multipliers with great stability at high temperatures. Beryllium intermetallic compounds, called beryllides such as Be₁₂Ti, are the most promising materials for use as advanced neutron multipliers. However, few studies have been conducted on the development of mass production methods for beryllide pebbles. A granulation process for beryllide needs to have both low cost and high efficiency. To fabricate beryllide pebbles, a new granulation process is established in this research by combining a plasma sintering method for beryllide synthesis and a rotating electrode method using a plasma-sintered electrode for granulation. The fabrication process of the beryllide electrode is investigated and optimized for mass production. The optimized beryllide electrode exhibits higher ductility and can be sintered at a lower temperature for a shorter time, indicating that it is more suitable not only for withstanding the thermal shock from arc-discharge during granulation but also for producing the beryllide pebbles on a large scale. Accordingly, because these optimization results can reduce the time required for electrode fabrication by 40%, they suggest the possibility of great reductions in time and cost for mass production of beryllide pebbles.     

Conceptual design of a water cooled breeder blanket for CFETR

China Fusion Engineering Test Reactor (CFETR) is an ITER-like superconducting tokamak reactor. Its major radius is 5.7 m, minor radius is 1.6 m and elongation ratio is 1.8. Its mission is to achieve 50–200 MW of fusion power, 30–50% of duty time factor, and tritium breeding ratio not less than 1.2 to ensure the self-sufficiency. As one of the breeding blanket candidates for CFETR, a water cooled breeder blanket with superheated steam is proposed and its conceptual design is being carried out. In this design, sub-cooling water at 265 °C under the pressure of 7 MPa is fed into cooling plates in breeding zone and is heated up to 285 °C with saturated steam generated, and then this steam is pre-superheated up to 310 °C in first wall (FW), final, the pre-superheated steam coming from several blankets is fed into the other one blanket to superheat again up to 517 °C. Due to low density of superheated steam, it has negligible impact on neutron absorption by coolant in FW so that the high energy neutrons entering into breeder zone moderated by water in cooling plate help enhance tritium breeding by ⁶Li(n,α)T reaction. Li₂TiO₃ pebbles and Be₁₂Ti pebbles are chosen as tritium breeder and neutron multiplier respectively, because Li₂TiO₃ and Be₁₂Ti are expected to have better chemical stability and compatibility with water in high temperature. However, Be₁₂Ti may lead to a reduction in tritium breeding ratio (TBR). Furthermore, a spot of sintered Be plate is used to improve neutron multiplying capacity in a multi-layer structure. As one alternative option, in spite of lower TBR, Pb is taken into account to replace Be plate in viewpoint of safety. In this contribution, study on neutronics and thermal design for a water cooled breeder blanket with superheated steam is reported.     

Deuterium retention of boron-titanium and reduction of deuterium retention after helium ion irradiations

Deuterium ion irradiations with an ion with energy of 1.7 keV were conducted for boron-titanium (B-Ti) film prepared by electron beam evaporation and hot pressed titanium-boride, TiB₂. The amount of retained deuterium was measured for these materials using a technique of thermal desorption spectroscopy. The amount of deuterium retained in TiB₂ was comparable with that in B-Ti. Desorption peaks of deuterium in B-Ti were 470 K and 620 K, corresponding to a desorption in the low temperature regime observed in boron (B) and a desorption in titanium (Ti), respectively. The desorption peaks in TiB₂ were 620 K and 750 K, which correspond to the desorption in Ti and that in the high temperature regime in B, respectively. The desorption temperature in B-Ti was approximately 100 K lower than that in TiB₂. This difference is discussed based upon chemical bindings and amorphous/crystal structures of B-Ti and TiB₂. Irradiation of helium ion with energy of 5 keV was conducted for B-Ti after the deuterium ion irradiation. The amount of retained deuterium decreased and the desorption temperature shifted to the lower temperature regime, as the helium ion fluence increased. The shift to the low temperature regime is due to the enhancement of amorphous structure of B in B-Ti.     

Thermal conductivity of rare earth-uranium ternary oxides of the type RE6UO12

The knowledge of thermophysical properties of the rare earth uranium ternary oxides of the type RE₆UO₁₂ (RE=La, Gd and Dy) is essential to understand the fuel performance during reactor operation and for modeling fuel behavior. Literature on the high temperature properties of this compound is not available and there is no report at all on the thermal conductivity of these compounds. Hence a study of thermal conductivity of this compound has been taken up. The compounds were synthesized by a solution combustion method using metal nitrates and urea. Thermal diffusivity of these compounds was measured by the laser flash method in the temperature range 673-1373 K. The specific heat data was computed using Neumann-Kopp’s law. Thermal conductivity was calculated using the measured thermal diffusivity value, density and specific heat data for different temperatures. The temperature dependence of thermal conductivity and the implication of structural aspects of these compounds on the data are discussed here.     

Investigation of the packing structure of pebble beds by DEM for CFETR WCCB

Li₂TiO₃/Be₁₂Ti mixed pebble beds with multi-sized particles are one of the potential candidates for the WCCB (water-cooled ceramic breeder blanket) of the CFETR (China Fusion Engineering Test Reactor). To meet the neutronics requirements of a WCCB, a study of the packing structure of the concerned pebble bed is necessary. In this paper, the discrete element method (DEM) is applied to produce a prototypical blanket pebble bed by directly simulating the contact state of each individual particle using basic interaction laws. According to the current simulation, the packing factor of a mono-sized pebble bed is 0.62–0.64, while the value will become more than 0.75 for Li₂TiO₃/Be₁₂Ti mixed breeding pebble bed with a diameter ratio of not less than 5 as well as an appropriate mixed volume ratio, and thus can meet the neutronics requirements.     

Calculations of thermodynamic properties of PuO2 by the first-principles and lattice vibration

Plutonium dioxide (PuO₂) is a key compound of mixed oxide fuel (MOX fuel). To predict the thermal properties of PuO₂ at high temperature, it is important to understand the properties of MOX fuel. In this study, thermodynamic properties of PuO₂ were evaluated by coupling of first-principles and lattice dynamics calculation. Cohesive energy was estimated from first-principles calculations, and the contribution of lattice vibration to total energy was evaluated by phonon calculations. Thermodynamic properties such as volume thermal expansion, bulk modulus and specific heat of PuO₂ were investigated up to 1500 K.     

Study of safety features and accident scenarios in a fusion DEMO reactor

After the Fukushima Dai-ichi nuclear accident, a need for assuring safety of fusion energy has grown in the Japanese (JA) fusion research community. DEMO safety research has been launched as a part of Broader Approach DEMO Design Activities (BA-DDA). This paper reports progress in the fusion DEMO safety research conducted under BA-DDA. Safety requirements and evaluation guidelines have been, first of all, established based on those established in the Japanese ITER site invitation activities. The radioactive source terms and energies that can mobilize such source terms have been assessed for a reference DEMO concept. This concept employs in-vessel components that are cooled by pressurized water and built of a low activation ferritic steel (F82H), contains solid pebble beds made of lithium-titanate (Li₂TiO₃) and beryllium–titanium (Be₁₂Ti) for tritium breeding and neutron multiplication, respectively. It is shown that unlike the energies expected in ITER, the enthalpy in the first wall/blanket cooling loops is large compared to the other energies expected in the reference DEMO concept. Reference accident event sequences in the reference DEMO in this study have been analyzed based on the Master Logic Diagram and Functional Failure Mode and Effect Analysis techniques. Accident events of particular concern in the DEMO have been selected based on the event sequence analysis and the hazard assessment.     

Molecular-orbital method for evaluating compound semiconductor range parameters

Using a molecular-orbital method, the range parameters of compound semiconductors are treated. The calculated results indicate that all III–V compounds and II–VI compounds deviate positively and negatively, respectively from Bragg's rule, and that the deviation coefficient does not depend on the implant energy but depends on the chemical bonding of the compounds. In addition, the calculated electronic stopping power of range parameters in negatively deviating systems (He⁺ → CdS and CdTe, and B⁺ → HgCdTe) and positively deviating systems (Li⁺ → Al₂O₃, Si⁺ → GaAs, Be⁺ → InP and NM⁺ → GaP) are in good agreement with experimental results. The theoretical model and the method used for calculating are discussed.     

On the anomalous stress-dependence of creep rate in precipitation strengthened alloys

The stress and temperature dependence of secondary creep rate have been analysed in the temperature range of 773–823 K for a 22% Cr-34% Ni austenitic steel (alloy 800) strengthened by a small volume fraction of γ′(Ni₃Ti, Al). In this respect two regimes have been distinguished at low and high stresses with the activation energies corresponding to those of the grain boundary and bulk diffusions, respectively. The very high stress-dependence (20) observed at elevated stresses, in comparison with those at low stresses (3–5), is shown to be enhanced by the metastability of the matrix and the resultant marked deformation inequalities during secondary creep. The effect of prior cold working and ageing are discussed. A correlation between low stress and high stress data through internal friction stress estimations is sought, and the possibility of the Coble creep mechanism becoming operative at low stresses is foreseen.     

Towards more precise Be and Cl data from measurements at the 10 level: Influence of sample preparation

The spreading application of accelerator mass spectrometry (AMS) to the geosciences will require measurement of increasing numbers of samples with low ¹⁰Be/⁹Be and ³⁶Cl/Cl isotopic ratios. To distinguish radionuclide concentrations in samples from corresponding processing blanks, samples must be prepared using stable isotope carriers with low intrinsic radionuclide concentrations. Measurements at different AMS facilities have shown that commercially available ⁹Be carriers rarely meet these requirements and use of ⁹Be carriers prepared from Be-containing minerals such as Be₂SiO₄ is advisable. For precise determinations at the low 10⁻¹⁴ level, samples need to produce the highest ⁹Be currents possible. Measurements performed at the two AMS facilities in France show that mixing BeO with Nb powder generally yields higher ⁹Be currents than mixing with Ag powder. Contamination of BeO by other elements such as Ti or Al will reduce the current by a simple dilution effect, thus limiting the statistical precision with which ¹⁰Be can be determined. In the case of ³⁶Cl analyses, repeated water-leaching of calcite samples sufficiently removes all atmospheric ³⁶Cl contamination, allowing determination of terrestrial cosmogenic in situ produced ³⁶Cl concentrations for surface exposure dating.     

A review of physical and mechanical properties of titanium beryllides with specific modern application of TiBe12

Titanium beryllide with the composition TiBe₁₂ has been identified as a potential alternative to beryllium metal for neutron multiplier applications in nuclear fusion reactors such as ITER and DEMO. TiBe₁₂ stands out from other beryllides for fusion because it has the highest neutron-multiplication characteristic, with the added benefit of higher temperature performance capability compared to beryllium metal. To date, little information has been available on the physical and mechanical properties of TiBe₁₂ despite an extensive R&D effort to characterize many beryllide intermetallic compounds in the U.S. from 1956 to 1970. This paper compiles data pertaining to TiBe₁₂ which are taken from several reports written during the referenced time period. This important historical work, which until now has only existed in hard copy reports in private technical libraries, is summarized for current relevance and subsequently, made available in electronic format as a technical reference and basis for planning future work.     

Dynamic Monte-Carlo modeling of thermal desorption of H2 from H irradiated graphite

Thermal desorption of hydrogen molecules from H⁺ irradiated graphite is studied using dynamic Monte Carlo simulation. The purpose of this study is to understand the experimentally observed phenomena that the thermal desorption of H₂ from the graphite exhibits sometimes single desorption peak, sometimes double peaks, and even three desorption peaks under certain circumstances. The study result reveals that the fluence of pre-implanted H⁺, the concentration of trap sites, porosity, and mean crystallite volume are important parameters in determining the number of desorption peaks. It is found that low implantation fluence and high concentration of trap sites easily lead to the occurrence of single desorption peak at around 1000 K, and high implantation fluence and low concentration of trap sites favor the occurrence of double desorption peaks, with a new desorption peak at around 820 K. It is also found that small porosity of graphite and large crystallite volume benefit the occurrence of single desorption peak at around 1000 K while large porosity of graphite and small crystallite volume facilitate the occurrence of double desorption peaks, respectively, at around 820 and 1000 K. In addition, experimentally observed third desorption peak at lower temperature is reproduced by simulation with assuming the graphite containing a small concentration of solute hydrogen atoms.     

A critical examination of the thermodynamics of water adsorption on actinide oxide surfaces

The reversible adsorption of water from actinide oxide surfaces is examined from several viewpoints in this article. A reinterpretation and critical look at the previously published thermodynamic values for desorption of water from PuO₂ [J. Phys. Chem. 77 (1973) 581] are reexamined in light of more recent mathematical treatments of thermal desorption data from high surface area materials. In addition, the time and temperature dependent process of water adsorption/desorption in closed system experiments is examined using chemical kinetics modeling. A simple experimental method and mathematical treatment of determining adsorption enthalpies based upon a closed system is also described. The desorption enthalpy for reversibly adsorbed water from PuO₂ is determined to be a function of adsorbate coverage with values ranging from 51 to 44 kJ mol⁻¹ for coverages of one to several monolayers (MLs). Consistent desorption enthalpy values are obtained using either approach thus highlighting the importance of proper interpretation of adsorption parameters determined from high surface area powders. Reversible adsorption/desorption equilibrium of water with actinide oxide materials is discussed from the practical standpoint of storage and subsequent pressurization of containers. These results obtained from PuO₂ surfaces are consistent with desorption enthalpies of water from a low surface area UO₂ that has been measured using ultra-high vacuum thermal desorption mass spectroscopy to be 42.2 kJ mol⁻¹.     

Toughness behaviour of the steel X 20 CrMoV 12 1 — Results of optimizing the base- and weld metal

The 12% Cr steels are frequently used in German power plants for tubings, pipes, rotors, and blades. The maximum operating temperature is limited by their creep strength properties to about 550°C. There are applications at even higher temperatures. Sufficient materials toughness is required for the base metal and weld metal to withstand sudden load changes. This is of special interest for use in nuclear power plants. Under operating conditions at elevated temperatures microstructural changes occur which greatly influence the toughness properties of both base metal and weld metal. This paper presents the results of ageing treatments at 550°C, carried out with a 12% Cr steel (DIN X 20 CrMoV 12 1) specifically optimized for toughness. The decrease in toughness is already evident at ageing times as low as 1000 h for conventional and optimized material. This drop in toughness is tentatively explained by differences in grain sizes and carbide content (M₂₃C₆ carbides). Detailed investigations indicate that additional carbide precipitation may significantly contribute to the decrease in toughness.     

Ti87.5Hf12.5合金的贮氢性能

测定了Ti87.5Hf12.5合金的吸氢体膨胀率和氢化物热稳定性,并与Ti及TiZr、TiV和TiNb等a相合金的相应特性进行了对比.TiHf合金具有最小的吸氢体膨胀率和最高的氢化物共析转变温度.Hf的添加显著长大了TiH2的晶格常数.测试了TiHf合金的吸放氢动力学特性和吸氢PCT曲线,Hf的添加未显著改变Ti的吸氢热力学特性,外推室温吸氢平衡压与Ti的相当.     

Profiling of titanium implanted into iron and nickel with the reaction 48Ti (p, γ)49V

A profiling technique for titanium is described which is based on an analog resonance in the cross section of the reaction ⁴⁸Ti(p, γ)⁴⁹V at E_P = 1.361 MeV. Primary γ radiation of the energy E_γ = 7.963 MeV is measured high detection efficiency is achieved. The properties of the technique are discussed and examples of its applications to Ti-implanted metals are given.