Metallic Fission Product Retention of Coated Particles with Ceramic Kernel Additives

The retention of metallic fission products in coated particles with ceramic kernel additives is studied out-of-pile and in-pile. The ceramic additives are easily introduced without any significant change of kernel fabrication processes. The excellent efficiency of alumina-silica kernel additives for retaining ⁹⁰Sr and ¹⁴⁰Ba is demonstrated in-pile: The fractional release is reduced by two orders of magnitude. Silver-110m is not retained by the kernel additives. Cesium forms compounds in the alumina-silica additives, which become unstable at temperatures above 1400°C (1673 K). At normal high-temperature gas-cooled reactor operation temperatures [1000 to 1200°C (1273 to 1473 K)], the diffusion coefficient of cesium in oxide kernels with alumina-silica additives is reduced by about two orders of magnitude. The effective diffusion coefficients in these kernels are given by the equationD_eff = 5.649 × 10⁴ cm² s⁻¹ exp (−63 833.5/T)[D_eff = 5.649 m² · s⁻¹ exp (−63 833.5/T)] .