All of the remaining compatibility tests are proceeding as scheduled. Results of the 20,000-hr compatibility tests with nonradioactive SrF/sub 2/ show that, with one exception, attack of the specimens by the SrF/sub 2/ after 20,000 hr is no greater than after 6000 and 12,000 hr. The one exception involved Haynes Alloy 25 specimens tested at 1000/sup 0/C. These test specimens exhibited isolated subsurface voids to depths of 0.025 in., although the general surface attack was only about 0.001 inches. The cause of the void formation has not yet been determined. Tests with Hastelloy S and Hastelloy C-4 at 600 to 800/sup 0/C for 2500 hr show that oxidation of the two alloys adheres to the parabolic rate law. Both alloys from adherent oxide layers over the temperature range of interest. Intergranular attack, pitting, and subsurface void formation increase sharply with increased oxidation temperature with both alloys, and at 800/sup 0/C the depth of metal exhibiting oxidation damage is several times greater than the thickness of the oxide layer.

The 20,000-hr compatibility tests using WESF /sup 90/SrF/sub 2/ have been completed. The test capsules were shipped to Oak Ridge National Laboratory (ORNL) and metallographic examination of the test specimens is now underway. Work continues on the final design of the prototype outer capsule. Efforts are underway to obtain the Hastelloy S and Hastelloy C-4 to be used in fabricating the prototype outer capsules. Puncture testing of the stand-in steel outer capsule was carried out without damage to the capsule. Effort continued on impact testing of the stand-in capsule. Tests to measure the oxidation rates of Hastelloy S and Hastelloy C-4 in air at 600 to 800/sup 0/C are continuing. Short-term test data for up to 2500-hr exposure indicated that oxidation of the two alloys adhered to parabolic rate relationships. Specimens oxidized for 5000 hr and 7500 hr exhibited erratic oxidation behavior, and the average oxidation rates were less than predicted by parabolic rate equations developed from the short-term rate data. Room-temperature tension testing of specimens oxidized in air at 600 to 800/sup 0/C for up to 7500 hr indicated that oxidation had no significant effect upon the room-temperature tensile properties of the two alloys.

All experimental activities related to the Strontium Heat Source Development Program have been completed. The only remaining activities are preparation and issuance of final reports that summarize program results. This report represents the last of the program quarterly progress reports that will be issued.