Development of Fabrication Technology for Oxidation-Resistant Fuel Elements for High-Temperature Gas-Cooled Reactors

Abstract

Japan Atomic Energy Agency (JAEA) has developed fabrication technology for oxidation-resistant fuel elements to improve the safety of high-temperature gas-cooled reactors in severe oxidation accidents on the basis of its previous research. Simulated fuel particles (alumina particles) were coated with a mixed powder of Si, C and a small amount of resin to form over-coated particles, which were molded and sintered by hot-pressing to form simulated oxidation-resistant fuel elements with a SiC/C mixed matrix, where the SiC was formed by reaction bonding. Simulated oxidation-resistant fuel elements with a matrix whose Si/C mole ratio (about 0.551) was three times as large as that in previous research were fabricated. No Si peak was detected by X-ray diffraction of the matrix. A monoaxial compressive fracture test was carried out, and the fracture stress was found to be more than three times as large as the standard for fuel compacts of High Temperature Engineering Test Reactor (HTTR). Better oxidation resistance than that of an ordinary fuel compact with a ordinary graphite matrix was confirmed by an oxidation test in 20% O 2 at 1673 K. All simulated coated fuel particles remained in specimen after 10 h oxidation.

A statistical approach for modelling the effect of hot press conditions on the mechanical strength properties of HTGR fuel elements

“…(2) Manufacturing overcoated particles (Aihara et al, 2019a) The material powder of the matrix was dredged over the simulated CFPs (alumina beads with a diameter of approximately 1 mm) to form the overcoated particles. After they were moistened with ethanol, the simulated CFPs were rolled in a machine for sugar-coating tablets when fabricating overcoated particles.…”

“…The fabrication method for the fuel element or the simulated fuel element, such that all the volume of the material of the matrix becomes the overcoat layer before molding, is called the overcoat method. (3) Molding and sintering (Aihara et al, 2019a) The overcoated particles were molded and hot pressed. The pressure, heating and cooling rate were 9.8 MPa and 10 °C/min, respectively.…”

“…the SiC and carbon (C) mixture matrix by the reaction sintering of silicon (Si) and C powders in Japan (Ikawa et al, 1978) (Ikawa et al, 1977) (Aihara et al, 2019a) (Aihara et al, 2019b).…”