FISSION-PRODUCT RELEASE FROM ZRC-COATED FUEL-PARTICLES DURING POSTIRRADIATION HEATING AT 1800 AND 2000-DEGREES-C

The ZrC coating layer is a candidate to replace the SiC coating layer of the Triso-coated fuel particles for high-temperature gas-cooled rea ctors. Post-irradiation heating tests of the ZrC-Triso coated UO2 part icles were performed at 1800 degrees C for 3000 h and at 2000 degrees C for 100 h to study the release behavior of fission products. The fis sion gas release monitoring and the X-ray microradiography revealed th at no through-coating failure occurred during the heating tests. The h igh cesium retention of the ZrC-Triso coated fuel particles was confir med up to 1800 degrees C. The diffusion coefficient for cesium in the ZrC layer was more than two orders smaller than that in the SiC layer at 1800 degrees C. The diffusion coefficient for ruthenium in the ZrC layer was almost the same as that for cesium in the SiC layer. (C) 199 7 Elsevier Science B.V.