periods each last 6 months. The experiment in the TABLE II chamber containing MHFT-27 was terminated (see Section J1.D.2). Two additional chamber experiments were started underarid winter conditions (3 to 28°C, 21 to 87% RH). Three other experiments were started under humid winter conditions. All seven current chamber TERRESTRIAL ENVIRONMENTAL CHAMBER EXPERIMENTS Experiment Number experiments are now operating under summer conditons, two in arid summer weather (26 to 53°C, 7 to 33% RH), the other five under humid conditions. The fuel material sample was placed in the center of the tray on the soil surface. Each sample under humid conditions received a 3-cm rain once a week. Therainsfor arid conditions occurred approximately once a month during the winter. There have been no 1 MHFT-12 chunks on loam: 6-21-73 2A MHFT-23 in GIS on sand; humid climate 6-10-75 3 MHFT-12 fines on loam; humid climate 9-27-73 6 MHFT-50 fines on loam: circular soil partitioner; humid climate 4-9-75 7 MHFT-27 fines on sand; arid climate 2-25-75 8 MHFT-50 chunks on loam: circular soil partitioner; humid climate 4-9-75 MHFT-27 chunks on sand; arid climate 2-26-75 humid climate rains during the first three months of arid summer. The rainwater that percolates through the soil is analyzed for plutonium. The condensate from the refrigeration-type dehumidifier in the chamberconditioning system is also analyzed to get a relative indication of the airborne plutonium in the chamber. Core samples of the soil are collected at approximately 6-monthintervals. Each core is divided into 5 to 14 sections that are analyzed separately to determine the plutonium variation with depth in the soil. Smail air samplers, fitted with approximately 40- mm-diam filter papers, were operated several times in two chambers to measure the airborne plutonium. The filter papers were changed frequently during operation, and the plutonium was measured by counting the papers and in somecasesbydissolving them and scintillation-counting the resultant solutions. Time-lapse movies were taken in four chambers during rains. Emissions from some fuel samples were studied by time exposure photographs, withoutex- Date Started Description 10 Photographsof the emissions from the large pieces © in the near-ir, visible, and near-uv spectral regions showed that the external temperature of the pieces was 250 to 300°C, and that an air glow around them was emitted mainly in the visible region, although some of it may have been uv. This air glow was probably caused byionization of air by the alpha or gamma activity of the pieces. Plutonium airborne concentrations increase during periods of rain on the large pieces. This effect results in a greater plutonium pickup from theair by the dehumidifier, which can be measured by plutonium analyses in the dehumidifier condensates Analyses for a period of 2 months are shownin Fig. 1. The explanation seems to be that material spalls from the hot pieces of PPO because of thermal shock when the cold rain first hits them. Spallation has ternal lighting, in the near-ir, visible, and near-uv marized in Table I. 1. MHFT-12. This was a PPOtest sphere for the Multi-Hundred Watt (MHW) program which shattered during a simulated reentry and impact. The sphere fragments were removed from the container andsorted by size. The pieces with diameters greater than 6 mm, weighing 224 g, were placed in one environmental test chamber on June 21, 1973, and 28 g of 0.01- to 6-mm-diam material was placed in another on September 28, 1973. These experiments are now in their third summerin a humid environment. & rT —_- 7 © i Pu in Condensate (ng/day) periments are currently under way. They are sum- NEDO OH A a1 D. Test Samples and Results Seven terrestrial environmental chamber ex- PE J y 1 } i J “T q Diagonallines indicate periods cf i ceilection in which relas cccurrad sk USS regions of the spectrum. 20 «25 30.35 Fig. 1. Effect of rain on plutonium content of dehumidifier condensates. 1 5