Post-irradiation SEM study of ZrC-based TRISO coatings from the PYCASSO experiments

Hania, R.*; Mnard, G.*; Aihara, Jun ; Ueta, Shohei   ; Knol, S.*; De Jong, A.*; Van den Berg, F.*; Van Staveren, T.*; De Groot, S.*

The PYCASSO irradiation experiments have been conducted to determine the effect of irradiation at high temperature on the properties of various coating materials of the coated fuel particle. One part of PYCASSO is to evaluate the advanced barrier material ZrC. Pyrocarbon (PyC) / ZrC-coated ZrO and AlO particles fabricated by JAEA were irradiated by HFR at 900 C and 1,100 C, at the same flux level up to approximately 2 dpa. Samples of irradiated and unirradiated particles are under investigation using an electron microscope, with the aim to identify irradiation effects and the influence of the heat treatment after the fabrication on the ZrC microstructure. Preliminary results of this SEM study indicate that whereas the heat treatment at 1,800 C prior to irradiation induces significant grain growth near the ZrC edges, embrittling the ZrC layer and weakening the iPyC-ZrC interface, irradiation has no noticeable effect on microstructure and coating strength.