reentry from orbit and impact with the earth, so that the source will be safely contained until it is recovered. Although existing designs have proved more than adequately safe, the Office of the Assis- off the rainwater that percolates through thesoil. The hottom of the tray tapers to a pipe that runs to the outside of the chamber so this water can he collected. the ERDA Division of Space Nuclear Systems con- B. Soils tant Director, Safety and Reliability Programs, of tinually seeks more information ahout the heat sources to improve their safety. As part of this program, LAS is studying the interaction of 7°8Pu fuel material with seawater, fresh water, and marine organisms, and withair, soil, and rain to supply data for design of even safer heat sources. Several chemical forms of 2°®Pu have been used as heat. sources. The forms now in use or being studied for future use are plutonia-molybdenum cermet (PMC), and various pressed shapes of pure plutonium dioxide (PPO). We have run several aquatic experiments using PMC, but all our terrestrial experiments have involved PPO. Discussions of details of the experiments are intentionally brief and will be repeated in subsequent progress reports. The main purpose of these reports is to compile in one convenient reference all usable About 1.4 Mg each of loam, clay. sand, and silt loam were obtained for terrestrial experiments. Compositional analyses of these soils were provided by the U. S. Soil Conservation Service Laboratory at Riverside, California (Table I). Pressure plate moisture measurements are planned for these soils. C. Test Conditions and Analyses Performed The first three experiments were started with the chambers programmed for humid summer conditions (20 to 40°C, 87 to 96° RH). Camsinstalled later provided humid winter conditions (0 to 17°C. 71 to 100% RH). The alternate summer and winter data venerated in the LASL experiments. The com- TABLE I pilation will be updated each quarter. When an experiment or set of experiments is completed or terminated, a final topical report will be issued and that phase of the work will not be included in sub- COMPOSITION OF SOILS USED IN TERRESTRIAL EXPERIMENTS? sequent quarterly reports. Il. BEHAVIOR OF *8pu TERRESTRIAL ENVIRONMENTS FUEL IN (James H. Patterson, Nicholas Vanderborgh. and George M. Matlack) A. Environmental Test Chambers Meaningful data on the environmental effects of the radiation and heat from radivisotope heat sources can best be obtained under simpler, less varied conditions than exist normally in nature. Use of environmental test chambers permits selection of the parameters to he tested and ensures control over them. Determination of the effects of these parameters on the fuel material and simulation of different climates and soils are also possible. Each environmental test chamber has aninterior volume of 1.8m" and can be programmedfor diurnal temperatures of ~20 to 95°C and relative humidities of 25 to 100%. A manually operated spray system simulates rainfall at rates as high as 10 em/h. Each chamber contains a 0.9- by 0.9-m tray, filled toa depth of 0.3 m with soil. The soil is supported by a grill covered with a thin perforated plate (o drain Loam Clay Silt Loam Sand Sand (%) 49,5 1.5 25.3 88.6 Silt. (%) 37.6 31.4 60.1 4.6 Clay (3) 12.9 67.1 14.6 6.8 C, organic (%) 0.6 Carbonate as CaCO3(%) trace H20 at 15 burs (%) 7.6 H20 at saturation(%) 40 0.12 0.03 8 10 23.8 7.5 0.01 4 2.6 91 45 22 pH Ca(neq/100 g) 8.0 16.3 7.8 43.9 8.4 20.4 9.1 17.8 Mg (meq/100 g)} 1.9 10.2 3.7 1.7 Na(meq/100 g) 0.5 4.6 3.5 0.9 K(meq/190 g) 1.0 1.1 0.5 0.5 13.6 42.0 14.7 6.0 0.6 4.2 3.3 0.6 4 te Cation exch cap Elect. Conductivity maho/cim Clzy — mincral ratios: Mica --- --- Montmorillonite 3 S 5 5 Kaolinite 3 2 3 3 "Soil analyses provided by the U. S. Soil Conservation Service Laboratory, Riverside, CA.