Present efforts in Study 3, entitled ''Evaluation of Test Methods and Properties of Candidate Encapsulation Materials,'' are concerned primarily with evaluation of the properties of candidate encapsulation materials and processes which have been identified. Specifically, cover materials for modules, and adhesives for bonding cells to cover materials and for bonding cover materials to other encapsulation-system components, are being screened in environments including UV radiation, temperature cycling, and high relative humidity. Results of the evaluations to date are described. These efforts include investigations of both polymeric and glass encapsulation materials. Efforts this quarter in Study 4, entitled ''Development of Accelerated and Abbreviated Testing Methods for Predicting Performance of Encapsulation Materials Over a 20-Year Lifetime,'' were concerned primarily with analyzing methods for discrimination among test methods with regard to precision, sensitivity, and cost. The background and procedures for such discrimination are discussed and examples are given.

The work reported includes studies of reactions between core materials and coolant impurities, basic fission product transport mechanisms, core graphite development and testing, the development and testing of recyclable fuel systems, and physics and fuel management studies. Materials studies include irradiation capsule tests of both fuel and graphite. Experimental procedures and results are discussed and the data are presented in tables, graphs, and photographs.

The stability of tensioned blades used in multiblade sawing does not seem to be the limitation in cutting with thin blades. So far, 0.010 cm thick blades have been totally unsuccessful. Recently, 0.015 cm blades have proven successful in wafering, offering an 0.005 cm reduction in the silicon used per slice. The failure of thin blades is characterized as a possible result of blade misalignment or from the inherent uncontrollability of the loose abrasive multiblade process. Corrective procedures will be employed in the assembly of packages to eliminate one type of blade misalignment. Two ingots were sliced with the same batch of standard silicon carbide abrasive slurry to determine the useful lifetime of this expendable material. After 250 slices, the cutting efficiency had not degraded. Further tests will be continued to establish the maximum lifetime of both silicon carbide and boron carbide abrasive. Electron microscopy will be employed to evaluate the wear of abrasive particles in the failure of abrasive slurry. The surface damage of silicon wafers has been characterized as predominantly subsurface fracture. Damage with No. 600 SiC is between 10 and 15 microns into the wafer surface. This agrees well with previous investigations of damage from silicon carbide …