Elements Of High Temperature Gas-cooled Reactor Research Articles

Investigation of the vibrating feeding system for sphericity separation of coated fuel particles using DEM

Using inclined vibrating plate (IVP) to gather spherical coated fuel particles is an important process in nuclear fuel particulate technology, especially in the manufacture of nuclear fuel elements for high-temperature gas-cooled reactor (HTGR). In order to get a satisfactory separation result, fuel particles are required to discharge uniformly and slowly into the IVP at a stable flow rate. To this end, the vibrating feeding system composed of a hopper and a new designed multi-layer multi-channel (MLMC) feeder is proposed in this paper to increase the discharge rate, optimize the uniformity of particle distribution and reduce the particle velocity near the outlet, which can produce a better separation of odd fuel particles. Subsequently, discrete element method (DEM) is used to investigate the motion of coated fuel particles in the feeding hopper. The accuracy of DEM is verified by comparing the experimental results with the simulation results. At the same time, the mass discharge rate (MDR) of particles in the hopper and the influence of geometry structure of hopper are studied. Finally, the motion of fuel particles in the new designed MLMC feeder is investigated, and the distribution characteristics of particles discharging out from the new feeder are analyzed. The simulation results demonstrate that the new designed feeding system can meet the optimal feeding requirements that the particles are discharged uniformly with the rather stable flow rate and the relatively lower particle velocity.

Insights into electrochemical behavior and anodic oxidation processing of graphite matrix in aqueous solutions of sodium nitrate

The electrochemical oxidation of graphite matrix from the simulative fuel elements for high-temperature gas-cooled reactor was investigated experimentally using NaNO3 solution as an electrolyte. The intercalation and oxidation reactions of graphite were investigated by means of cyclic voltammetry. In addition, the morphological changes of the graphite anodes at predetermined intervals of time during the electro-oxidation process were examined by scanning electron microscopy. The structural transformation of graphite was systematically characterized by different methods. Results showed that the electro-oxidation process induced oxygen-containing groups (i.e., hydroxyl, epoxide, carbonyl/ketone, and carboxyl groups) into the graphite backbone. Electrolytic graphite oxide presented a heterogeneous, indeterminate, and disordered system composed of crystalline and amorphous phases. The structure and microstructure of nuclear graphite, particularly its cracks and defects, primarily determined its destruction pathway during the electrolytic process. The mechanism of graphite lattice destruction could be attributed to the complicated interplay of water electrolysis, anionic intercalation, and gas evolution. The mechanical force caused by gas eruptions among the graphite lattice is the most important and essential factor favoring disintegration.