[en] Short communication

[en] The Solution High-Energy Burst Assembly II (SHEBA-II) has been in operation at Los Alamos National Laboratory for more than 4 yr. During that time it has been fueled exclusively with an aqueous solution of uranyl fluoride. However, because of the corrosiveness and viscosity of uranyl fluoride, it is planned eventually to use an aqueous solution of uranyl nitrate as fuel instead. This paper evaluates the likely change in spectrum and critical height accompanying this changeover and investigates its impact on a set of proposed experiments

No abstract available

[en] A study of a new type of low-power heat-producing reactor for space heating of small communities is presented. (author)

[en] The aim of calculations is to evaluate the evolution of the infinate multiplication factor (k_inf) during the irradiation of minor actinides, High Level Waste (HLWL) and Plutonium. The most important results are independently verified with Monte Carlo calculations. The relative importance of the main parameters affecting the k_inf was investigated by performing calculations with several minor actinide and plutonium concentrations as well as different ²³⁸U decontamination factors for HLW. The merit figure value for minor actinide alone, considering a constant neutron flux indicates that the best results are reached for minor actinide concentration equal to PWR spent fuel. The best plutonium burning results are obtained for a concentration (50.23 g/l) equal to the half of PWR spent fuel one. The simulations lead to two different reactor concepts: one for HLW burning and the other for plutonium burning purposes. To burn the HLW the most suitable reactor is an homogeneous one. This kind of reactor can effectively be utilised to burn minor actinide in low concentration (namely the PWR spent fuel). On the other hand an heterogeneous reactor with channels filled by all actinides present in PWR spent fuel with the exclusion of U isotopes with a concentration of 50 g/l can be studied

No abstract available

[en] The Solution High-Energy Burst Assembly (SHEBA), located at the Los Alamos Critical Experiments Facility, is a homogeneous liquid-fueled reactor that is being prepared for prompt burst operation. As part of the preparations, a reactor safety study was performed in support of the new SHEBA experiment plan. This study looked at the maximum power, total energy yield, and maximum transient pressures that may occur in the reactor during prompt burst operation. The goal of this study is to analyze the neutronic and hydrodynamic behavior of the reactor during burst operation, and to ensure that prompt burst operation does not damage the reactor or exceed the safety envelope of the facility's Safety Analysis Report (SAR)

[en] In this work, an uranyl nitrate homogeneous solution reactor for Mo⁹⁹ production was analysed. The uranyl nitrate solution fuel (20% enriched in U²³⁵) is contained in a cylindrical stainless steel tank, surrounded with light water as neutronic reflector. The reactor has 6 cadmium rods as control system. An helical heat exchanger is immersed into the solution. The heat is removed from the fuel by natural convection, while water circulation inside the exchanger is forced. The only purpose of this reactor is radioisotope production at lower costs. As compared to other radioisotope production options, it gives several advantages like small burnup to produce large quantities of Mo⁹⁹ operating at low power. The aim of this work is to study the neutronic characteristics in order to assess important parameters for reactor design and to set the main calculation options. This reactor core has been simulated and reactivity variations in normal and abnormal operation due to several phenomena were studied with MCNP, WIMS and TORT codes. One important factor during normal operation is reactor temperature variation, leading to fuel volumetric expansion and spectral effects. The reactivity change due to fuel volumetric expansion could be as large as 600 pcm and that due to spectral effects in fuel cross-sections could be an average change of 1000 pcm for 100 Celsius degrees fuel temperature variation. All calculations show very safe neutronic behaviors with large negative reactivity coefficients and good Mo⁹⁹ production

[en] Full text: A pilot homogenous reactor utilizing LEU has been developed by the Kurchatov Institute in Moscow along with their commercial partner TCI Medical. This solution reactor operates at levels up to 50 kilowatts and has successfully produced high quality Mo-99 and Sr-89. Radiochemical extraction of medical radionuclides from the reactor solution is performed by passing the solution across a series of inorganic sorbents. This reactor has commercial potential for medical radionuclide production using LEU U2SO4 fuel. Additional development work is needed to optimize multiple 50 kilowatt cores while at the same time, optimizing production efficiency and capital expenditure. (author)

[en] Steady natural convective flow fields were numerically and experimentally characterized for 0.7 Prandtl number fluids having constant, uniformly distributed, internal heat sources. The bounding isothermal walls containing the fluid were considered to be either a sphere or a cylinder of finite height. An instrumented cylinder containing radioactive tritium gas was used to demonstrate experimental and analytical agreement for local temperatures over a range of Grashof numbers. For the spherical geometry, a generalized correlation was obtained for the surface-averaged Nusselt number as a function of a modified Grashof number