[en] STREAM uses a pin-based slowing-down method (PSM) which solves pointwise energy slowing-down problems with sub-divided fuel pellet, and shows a great performance in calculating effective cross-section (XS). Various issues in the conventional resonance treatment methods (i.e., approximations on resonance scattering source, resonance interference effect, and intrapellet self-shielding effect) were successfully resolved by PSM. PSM assumes that a fuel rod has a uniform material composition and temperature even though PSM calculates spatially dependent effective XSs of fuel subregions. When the depletion calculation or thermal/hydraulic (T/H) coupling are performed with sub-divided material meshes, each subregion has its own material condition depending on position. It was reported that the treatment of distributed temperature is important to calculate an accurate fuel temperature coefficient (FTC). In order to avoid the approximation in PSM, the collision probability method (CPM) has been incorporated as a calculation option. The resonance treatment method, PSM, used in the transport code STREAM has been enhanced to accurately consider a non-uniform material condition. The method incorporates CPM in computing collision probability of isolated fuel pin. From numerical tests with pin-cell problems, STREAM with the method showed very accurate multiplication factor and FTC results less than 83 pcm and 1.43 % differences from the references, respectively. The original PSM showed larger differences than the proposed method but still has a high accuracy

[en] The objective of accident tolerant fuels (ATFs) research is developing innovative fuels that can mitigate the consequences of accidents. In order to fully mature ATF concepts and successfully implement ATF technologies in the commercial power plants, it would be important to understand the development status of proposed concepts, define research gap and priority, and gauge the time and effort remaining. Technology Readiness Levels (TRLs) are a systematic metric/measurement system that assesses the maturity of a particular technology and compares consistently the maturity between different types of technology. This paper will address the preliminary definition and criteria of TRLs for ATFs development and assess the evaluation and verification processes required for relevant technology to move to a higher TRL. A main attribute to gauge the fabrication process maturity for ATFs is the quantity of materials used for fabrication process and testing. The quantity can be measured as batch size and/or throughput rate. Fuel performance maturity is associated with the acquiring database of fuel properties and irradiation behavior to reduce sufficiently the uncertainty of safety and reliability for use of the fuel design

[en] Based on the observation that ignoring the angle dependency of multigroup resonance cross sections within a fuel pellet would result in nontrivial underestimation of the spatial self-shielding of flux, a parametrized spectral superhomogenization (SPH) factor library (PSSL) method is developed as a practical means of resolving the problem. Region-wise spectral SPH factors are calculated by the normal and transport corrected SPH iterations after ultrafine group slowing down calculations over various light water reactor pin-cell configurations. The parametrization is done with fuel temperature, U-238 number density, fuel radius, moderator source represented by Σ_modV_mod, and the number density ratio of resonance nuclides to that of U-238 in a form of resonance interference correction factors. The parametrization is successful in that the root mean square errors of the interpolated SPH factors over the fuel regions of various pin-cells are within 0.1%. The improvement in reactivity error of the PSSL method is shown to be superior to that by the original SPH method in that the reactivity bias of −200 pcm to −300 pcm vanishes almost completely. It is demonstrated that the environment effect takes only about 4% in the reactivity improvement so that the pin-cell based PSSL method is effective in the assembly problems

[en] This series of slides presents the changes in the design of fuel assemblies by Areva-NP. The main improvement was the use of the M5 alloy for the pin cladding that allows higher burnups. Till now about 1000 new fuel assemblies, totally made of M5 alloy (pin + structure) have been put in reactor and have allowed us to push forward the limitations of the previous generation. Another improvement is the use of uranium pellets doped with chromium, the feedback experience shows that the release of fission product gases can be reduced by 65% in power transients compared with classical pellets. Progress have also been made in the simulation of the in-core behaviour of fuel assemblies. These simulations have been validated on testing facilities like the KATHY loop at Karlstein. (A.C.)

[en] Highlights: • Methods of cyclic loading tests on the pebble beds were developed in DEM. • Size distribution and sphericity of the pebbles were considered for the specimen. • Mechanical responses of the pebble beds under cyclic loading tests were assessed. - Abstract: Complex mechanics and packing instability can be induced by loading operation on ceramic breeder pebble bed for its discrete nature. A numerical approach using discrete element method (DEM) is applied to study the mechanical performance of the ceramic breeder pebble bed under quasi-static and cyclic loads. A preloaded specimen can be made with servo-control mechanism, the quasi-static and dynamic stress-strain performances are studied during the tests. It is found that the normalized normal contact forces under quasi-static loads have the similar distributions, and increase with increasing loads. Furthermore, the relatively low volumetric strain can be absorbed by pebble bed after several loading and unloading cycles, but the peak normal contact force can be extremely high during the first cycle. Cyclic loading with target pressure is recommended for densely packing, irreversible volume reduction gradually increase with cycles, and the normal contact forces decrease with cycles.

No abstract available

[en] In the experiments on tangential fuel pellet injection in the TUMAN-3M tokamak an initiation of LH-transition or, in several scenarios—temporal (1–2 ms) confinement improvement with the following backwards transition was observed. To understand the possibility of the transitions, a model calculating the evolution of density and ion temperature profiles under the effect of source profile perturbation and plasma cooling created by pellet evaporation was developed. In the model, a diffusion coefficient depending on radial electric field shear value was used. Turbulence parameters are defined using a gyrokinetic simulation of the experiments with ELMFIRE code. Modeling results are in good agreement with experiments. Using the data obtained from the modeling, non-linear particle flux dependency on density gradient was analyzed; the existence of two stabile solutions for two confinement modes dependent on particle flux value was proved, in agreement with experiments. (paper)

[en] In view of the characteristics of pellets, the relation between perpendicularity and end circular run-out error was analyzed, and the perpendicularity detection system for nuclear fuel pellets was designed. Using the grating displacement transducer for measuring end circular run-out error during the pellet rotation course driven by a rotation stage, the system realized the pellet automatic detection.It obtained the resolution over 0.5 μm, the accuracy over 3.0 μm and the speed 3 pellets/min, and the functions such as data displaying in real time, rapid storage, alarm, and automatic report generation were endowed. The actual operation results indicated that the system was secure,stable and reliable. (authors)

[en] Recent progress in laser driven implosion is reviewed. Improvements in the uniformity of irradiation by laser beams on fuel pellets have achieved quantitative progress in implosion performance. The recent results of the direct drive-central ignition experiments give us confidence in achieving fusion ignition, burning and energy gain using a multi-beam megajoule laser with full implementation of beam smoothing techniques. Fast ignition research is also reviewed, which could give us a higher energy gain with lower laser energy. The science and technology of laser fusion power plants are beginning to attract wider attention, as forming the road map to achieve commercial power plants for cleaner, safer and abundant fusion energy

[en] A fission gas release model is presented, which solves the atomic diffusion problem with xenon and krypton elements tramps produced by uranium fission during UO₂ nuclear fuel irradiation. The model considers intra and intergranular precipitation bubbles, its re dissolution owing to highly energetic fission products impact, interconnection of intergranular bubbles and gas sweeping by grain border in movement because of grain growth. In the model, the existence of a thermal gradient in the fuel pellet is considered, as well as temporal variations of fission rate owing to changes in the operation lineal power. The diffusion equation is solved by the finite element method and results of gas release and swelling calculation owing to gas fission are compared with experimental data. (author)