•JA DEMO blanket concept requires 2.0 mm-sized Be12V and 0.2 mm-sized Li2TiO3 to achieve 80 % packing fraction.•A rotating electrode process could fabricate single-sized Be12V pebbles with from 0.3 ...to 2.7 mm.•An emulsion process could fabricate Li2TiO3 pebbles with 0.3 mm by controlling oil viscosity and oil flow ratio.•Li2TiO3 pebbles with 0.3 mm would be adoptable by loading bigger Be12V pebbles with 2.5 mm.
A JA DEMO blanket requires Be12V pebbles with 2 mm (or bigger) and Li2TiO3 with 0.2 mm as a mixed pebbles packing concept for achieving an 80 % packing fraction. The authors' group has achieved a significant milestone by successfully manufacturing Be12V pebbles through a pioneering rotating electrode process, marking a world-first achievement. Simultaneously, Li2TiO3 pebbles have been produced utilizing an emulsion process developed by the same research group. It is worth noting that most prior studies focused on pebbles with a 1 mm diameter, as this size was initially recommended for the ITER TBM before the introduction of the new packing concept. The rotating electrode process has successfully yielded Be12V pebbles measuring 2.5 mm or larger, and their characteristics have been thoroughly examined, offering a comprehensive overview of the current progress in Be12V pebble production. Furthermore, to meet the specific requirements of the JA DEMO blanket, experiments were conducted to fabricate smaller Li2TiO3 pebbles. It was discovered that Li2TiO3 pebbles with 0.3 mm could be successfully produced by adjusting the oil viscosity and flow ratio within the existing emulsion process system.
Summary
Merits in the inherent safety characteristics and multiple applications, cause the pebble‐bed‐type nuclear reactors, including the High‐Temperature Gas‐cooled Reactors, Fluoride‐salt‐cooled ...High‐temperature Reactors and Water‐cooled Pebble‐bed Reactors, to gain more focus in recent years. Thermal‐hydraulic characteristics in the pebble bed reactor core are of great significance to the safety evaluation and design of such reactors. Experimental investigations on the thermal‐hydraulics of different fluids in the pebble‐bed‐type of nuclear reactor core have been reviewed in this paper. Main experimental methods to determine the flow regime transition, convective heat transfer coefficients, and effective thermal conductivity have been summarized, with the merits and disadvantages discussed. Discussions are given on the main factors that can influence the flow, convective heat transfer and effective thermal conductivity in the pebble bed.
The solid type of tritium breeder materials is usually used in a pebble form because of the high packing factor, efficiency of tritium extraction, and advantage of thermal conduction between the ...structural materials. The breeder pebbles are required a good sphericity and uniform microstructure from the viewpoint of a packing factor and a release of bred tritium. Therefore, in this study, the lithium metatitanate (Li2TiO3) pebbles have been fabricated by powder injection molding process in order to secure a high sphericity of pebbles. In addition, the physical, mechanical, and thermal properties of the pebbles have been investigated. The Li2TiO3 green pebbles have been fabricated by using the powder injection molding process (PIM process). The diameter and sphericity of green pebbles were about 1.000 mm and 1.001, respectively. Then, the green pebbles were sintered at 1000 °C for 3 hr in air atmosphere. The diameter of sintered pebbles is about 0.95 mm. The volume shrinkage ratio was about 16 % during the sintering process. The uniform microstructure with open pores on the inside and outside of the sintered pebbles was observed.
Abstract
Several studies related to simplifying the modeling of pebble bed High-Temperature Reactor core (HTR) has been developed before. From some calculation on several MCNP models with a fueled ...pebble to dummy ratio 57:43, using a combination of several types of TRISO (TRi-structural ISOtropic particle fuel) unit and Pebble unit is modeled to achieve its first criticality. In this paper, some MCNP model that uses 27000 pebbles with a 57:43 ratio and 100% fueled pebble is created to be used on burnup calculation and to compare its k-eff and nuclide inventory. From this burnup calculation, it could be seen that SC (Simple Cubic) TRISO unit has faster calculation time followed by the HCP (Hexagonal Close Packed) TRISO unit and then the FCC (Face-Centered Cubic) TRISO unit. The BCC (Body-Centered Cubic) pebble unit had some consistent deviation from another pebble unit, and it still needs more study to know more about the reason behind it. It could be seen that if there are some dummy pebbles inside the reactor, then the deviation would be higher than if there is just fueled pebble inside the reactor. On the 57:43 ratio, the absolute average deviation of k-eff on burnup calculation is lower than 2% and 10% for nuclide inventory (mass). On 100% fueled pebble, it’s below 0.15% on k-eff absolute deviation and below 8% on nuclide inventory deviation.
•Effective thermal conductivity of the Li2TiO3 pebble bed was strongly dependent on a kind of atmospheric gases.•Effective thermal conductivity of the Li2TiO3 pebble bed was not significantly changed ...by the hydrogen concentration ratio in helium atmosphere within a range of less than 1.0 wt.%.•Applied axial compression load has influenced on the effective thermal conductivity of the Li2TiO3 pebble bed, especially at high temperature.•Obvious change of effective thermal conductivity with the value of compression load until 3 MPa was not observed.
Tritium breeder material in the solid-type of breeding blanket concepts is usually used in a pebble bed form because of the efficiency and convenience of tritium extraction. The pebble bed is continuously heated by the exothermal reaction between neutron and lithium-6 during the operation of a fusion reactor. Thus, a compression pressure is applied on the pebble bed by the thermal expansion of pebbles and container structure. Therefore, the accurate thermal properties of the pebble bed are one of the important design parameters to ensure a function and stability of the breeding blanket. This study aims at the investigation of the change on effective thermal conductivity of Li2TiO3 pebble beds under the operation conditions of breeding blanket.
The measurement of effective thermal conductivities of Li2TiO3 pebble beds has been performed by laser flash technique in several atmosphere gases, such as helium, nitrogen, and air, under the statically compression load controlled by specially design pneumatic device incorporated to the laser flash apparatus. Also, in the case of helium atmosphere, the effects of hydrogen concentration from 0.1 wt.% to 1.0 wt.% on the effective thermal conductivity were also investigated. The effective thermal conductivity of the Li2TiO3 pebble bed was strongly dependent on a kind of atmosphere gases, especially its thermal conductivity, in the relatively low temperature. However, the concentration of hydrogen in the helium atmosphere did not significantly affect the effective thermal conductivity of the pebble bed. Applied axial compression load has influenced on the effective thermal conductivity of the Li2TiO3 pebble bed, especially at high temperature. However, the obvious change of effective thermal conductivity with the value of compression load was not observed.
One Generation IV nuclear reactor, which uses a fluoride salt as a coolant, graphite reflector blocks as a moderator, and circulating buoyant TRISO pebbles as fuel is at an advanced stage of ...development. To characterize the seismic behavior of components of this reactor, validate numerical models for analysis, and develop recommendations for design, a set of earthquake‐simulator experiments on a scaled model of the reactor vessel and its internals was executed on a six‐degree‐of‐freedom earthquake simulator. The model was seismically isolated at its base using two types of spherical sliding bearings. The scaled model involved representations of the prototype reactor vessel, core barrel, reflector blocks, coolant, and spherical fuel pebbles. The material and geometric properties of different test components were selected based on a dynamic similitude scaling analysis and an approximate length scale of 0.4. Four sets of three‐component earthquake motions were used as inputs for testing. Instrumentation on the test specimen recorded the dynamic responses of the outer vessel, core barrel, and reflector‐block assembly, the hydrodynamic responses (sloshing and hydrodynamic pressure) of the liquid coolant, pebble consolidation under earthquake shaking, and the behavior of the isolation systems. This paper describes the design of the experiments and presents key results from the tests. The dynamic responses of the outer vessel, core barrel, and the reflector blocks revealed that the components responded as a unit for the intense shaking used in the experiments. The sloshing response of the fluid in a thin annulus near the perimeter of the vessel was heavily damped. The change in the packing fraction of the pebble bed under repeated, intense 3D earthquake shaking was less than 3%. Seismically isolating the vessel substantially reduced demands on its internal components.
•The pressure drop of unitary and binary pebble beds are studied.•In unitary beds, the "viscous" term coefficient varies with the void fraction.•In binary pebble beds, the "inertial" term coefficient ...depends on diameter ratio.•In binary pebble beds, the "viscous" term coefficient depends on bed homogeneity.•Increased diameter and volume ratio in binary beds lower tortuosity coefficient n.
This paper presents a study on the characteristics of purge gas pressure drop in unitary and binary pebble beds, considering different void fractions and diameter ratios. To model tritium purge gas in the breeder zones of blankets, a helium loop is constructed to provide a flow at 0.1–2.0 MPa with a maximum flow rate of 80 Nm3/h. The experimental results show that the pressure drop ∆P increases linearly with superficial velocity, temperature, and gas pressure, and is inversely related to particle diameter and void fraction. In unitary pebble beds, the coefficient for the "inertial" term remains constant and is unaffected by the void fraction, while the "viscous" term coefficient varies with the void fraction. In binary pebble beds, the pressure drop is influenced by the diameter ratio and volume fraction of large particles. The "inertial" term coefficient depends solely on the diameter ratio and increases with it, while the "viscous" term coefficient is influenced by the tortuosity packing coefficient which decreases as the particle diameter ratio and volume fraction of larger particles increase. These findings of pressure drop are significant for improving tritium extraction performance during the design process of the blanket system.
After the first concrete was poured on December 9, 2012 at the Shidao Bay site in Rongcheng, Shandong Province, China, the construction of the reactor building for the world's first high-temperature ...gas-cooled reactor pebble-bed module (HTR-PM) demonstration power plant was completed in June, 2015. Installation of the main equipment then began, and the power plant is currently progressing well toward connecting to the grid at the end of 2017. The thermal power of a single HTR-PM reactor module is 250 MWth, the helium temperatures at the reactor core inlet/outlet are 250/750 °C, and a steam of 13.25 MPa/567 °C is produced at the steam generator outlet. Two HTR-PM reactor modules are connected to a steam turbine to form a 210 MWe nuclear power plant. Due to China's industrial capability, we were able to overcome great difficulties, manufacture first-of-a-kind equipment, and realize series major technological innovations. We have achieved successful results in many aspects, including planning and implementing R&D, establishing an industrial partnership, manufacturing equipment, fuel production, licensing, site preparation, and balancing safety and economics; these obtained experiences may also be referenced by the global nuclear community.
Predicting the capability of decay-heat removal for a pebble bed of the high-temperature gas-cooled reactor is a cutting-edge issue in the research of generation IV advanced reactors. In this ...research, numerical simulations of heat transfer in the pebble bed reactor have been conducted by developing two kinds of models, a particle-scale model and a porous media model. The aim is to estimate the effect thermal conductivity of the pebble bed and predict the internal temperature field. The former model relies on the pebble–pebble conduction and radiation at a scale as fine as every fuel pebble. The latter one is an overall model at the scale mainly on the whole feature and capability of the pebble bed reactor. These two models have generated consistent results in an intermediate case considering the effective thermal conductivity for radiation and conduction of the pebbles. Based on this consistency, the pebble bed’s overall features of the internal field of the temperature field in pressurized helium have been well predicted. The simulation results validate the pretty good capability of the pebble bed reactor on decay-heat removal. The maximum temperature of the reactor core is limited to about 350 °C at the 7 MPa pressurized helium. This means the safety of the HTR-PM reactor could be reasonably guaranteed.
•A new SPH kernel by combining a polynomial and a reciprocal term is proposed.•Validated by dam-break, the kernel is used for natural convection in reactor cores.•Comparing to existing kernels shows the differences and (dis)-advantages of them.•Various temperature differences, channel numbers/lengths are simulated.•A mapping method is used to transfer particles’ velocity/temperature to Eulerian.
•Effects of spatial scale on modeling radiative heat transfer of packed particle beds are analyzed.•Long-range scale (LR) model is accurate for large conductivity ks≫kr or Λ>10.•Short-range scale ...(SR) model is inaccurate for ks≫kr but accurate for ks~O(kr) at low temperature.•Microscopic-scale (MS) model is the most accurate model used for correcting other models.•Over- and underestimation of radiative and conductive heat cause better prediction of SR at ks~O(kr).
Thermal radiation is important in high temperature packed pebble bed, which is still poorly understood. The present work is to analyze the effect of spatial scale in modeling thermal radiation of packed pebble beds. The long-range model (full integral scale), short-range model (partial integral scale) and microscopic models (sub-particle scale) are compared and analyzed with reference to existing correlations. In high temperature packed pebble beds, the long-range model takes into account all possible radiation between surrounding spheres, even those that are not direct Voronoi neighbors, whereas the short-range model considers only a portion nearby. It is found that when solid conductivity is much greater than the effective thermal conductivity of radiation (ks≫kr or Λ>10), the long-range model provides better results than the short-range model in predicting the radiative heat exchange. The short-range model overestimates solid conductivity at low temperatures (lower than 1215°C) when ks~O(kr) (or Λ<10) while underestimating radiative heat exchange. It therefore still provides predictions for total heat exchange that is in good agreement with experimental data in cases where the errors cancel out. Moreover, the short-range radiation model is more computationally efficient than the long-range model and microscopic model to compute view factor between particles of Voronoi neighbors.
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