The high temperature diffusion technique for fuel filling of some future direct drive cryogenic ICF targets may be unacceptable. The following describes a technique of fitting a 1 mm diameter x 6 ..mu..m thick glass microsphere with an approx. 50 ..mu..m O.D. glass fill tube. The process of laser drilling a 50 ..mu..m diameter hole in the microsphere wall, technique for making the epoxy joint between the sphere and fill tube, as well as the assembly procedure are also discussed.

The primary barrier to release of fission product from any of the fuel types into the primary circuit of the HTGR are the coatings on the fuel particles. Both pyrolytic carbon and silicon carbide coatings are very effective in retaining fission gases under normal operating conditions. One of the possible performance limitations which has been observed in irradiation tests of TRISO fuel is chemical interaction of the SiC layer with fission products. This reaction reduces the thickness of the SiC layer in TRISO particles and can lead to release of fission products from the particles if the SiC layer is completely penetrated. The experimental section of this report describes the results of work at General Atomic concerning the reaction of fission products with silicon carbide. The discussion section describes data obtained by various laboratories and includes (1) a description of the fission products which have been found to react with SiC; (2) a description of the kinetics of silicon carbide thinning caused by fission product reaction during out-of-pile thermal gradient heating and the application of these kinetics to in-pile irradiation; and (3) a comparison of silicon carbide thinning in LEU and HEU fuels.

A report to the community on the 1981 Razzle Dazzle.