Pacific Northwest Laboratory quarterly report to USERDA Advanced Nuclear Energy Systems, Space and Special Purposes Division, for July--September 1975

Progress during July to October 1975 in research on radioisotope heat sources is reported. The design of the long-term $sup 90$SrF$sub 2$ compatibility tests has been finalized. The effect of thermal aging on the impact strength of Hastelloy C-4 is being evaluated using Charpy test specimens. The solubility of SrF$sub 2$ in seawater and demineralized water was determined at 23$sup 0$C. The equilibrium concentration of Sr in demineralized water is greatly influenced by the presence of fluoride impurities in the SrF$sub 2$, whereas in seawater the presence of fluoride impurities has little effect on the Sr concentration. The effect of impurity fluorides and decay product (ZrF$sub 4$) on the melting point of SrF$sub 2$ was determined using differential thermal analysis. The lowest melting point observed in the system containing SrF$sub 2$, ZrF$sub 4$ and impurity fluorides found in WESF $sup 90$SrF$sub 2$ was 851 +- 5$sup 0$C. Two reports on potential applications of isotopes were prepared, and theoretical work continued on the effect of source geometry on the radiation efficiency of $sup 137$CsCl capsules. (LCL