[en] Although existing radioisotope thermoelectric generator designs have proved more than adequately safe, more information is continually sought about the heat sources to improve their safety. The work here includes studies of the effects on the heat sources of terrestrial and aquatic environments and also of the effects of the heat sources on various simulated environments. This progress report presents recent data from environmental chamber and aquatic experiments and gives the present status of the experiments

[en] Secondary ion mass spectrometry (SIMS) has been used to investigate changes that occur in an advanced Ir-0.3W alloy during high temperature aging. This alloy is used to clad ²³⁸PuO₂ heat sources used in thermoelectric generators for deep space reconnaissance satellites. Long-term direct contact with PuO₂ at 1400⁰C leads to physical and chemical changes within the cladding alloy that affect its metallurgical properties. SIMS was used to show that Cr, Fe, Ni, and in some cases O, diffuse from the PuO₂ into the alloy. Thorium and aluminum diffuse out of the alloy in these same regions. This SIMS study suggests that inward O diffusion and subsequent formation of ThO₂ on grain boundaries may stabilize the alloy against enhanced grain growth

[en] The SARP includes discussions of structural integrity, thermal resistance, radiation shielding and radiological safety, nuclear criticality safety, and quality control. Extensive tests and evaluations were performed to show that the container will function effectively with respect to all required standards and when subjected to normal transportation conditions and the sequence of four hypothetical accident conditions (free drop, puncture, thermal, and water immersion). In addition, a steady state temperature profile and radiation profile were measured using two heat sources that very closely resemble the GPHS. This gave an excellent representation of the GPHS temperature and radiation profile. A nuclear criticality safety analysis determined that all safety requirements are met

[en] Plutonium-238 oxide fuel pellets for the General Purpose Heat Source (GPHS) Radioisotopic Thermoelectric Generators to be used on the NASA Galileo Mission to Jupiter and the International Solar Polar Mission are produced and encapsulated in iridium alloy at the Savannah River Plant (SRP). Underbead cracks occasionally occur in the girth weld on the iridium-alloy-clad vent sets in the region where the gas tungsten arc is quenched. Grain-boundary structures and compositions were characterized by scanning electron microscopy/x-ray energy spectroscopy, electron microprobe analysis and scanning Auger microprobe analysis to determine the cause of weld quench area cracking. Results suggest that weld quench area cracking may be caused by gas porosity or liquation in the grain boundaries

[en] Possible DOD demands for up to 1 MW thermal of heat sources could be partially met by increasing SRP Pu-238 production. The Pu-238 would be an alternate or supplement to Sr-90 in these heat sources. There is a growing surplus of Np-237 target material which could be used to produce high-assay Pu-238 (83.5%). In addition SRP produces low assay Pu-238 (approx. 27%) that could be extracted instead of being sent to the waste tanks. About 216 kg or 121 kw thermal of additional high-assay Pu-238 could be produced at SRP through FY1997; it would produce power at an incremental cost of approx. $1160/watt. About 77 kg or 44 kw thermal of low assay Pu-238 could also be recovered through FY1997; it would generate power at approx. $1850/watt. These quantities would supply only a fraction (approx. 1/6 of the 1 MW demand projection. Also the costs are considerably higher than the costs for Sr-90 fission product heat sources. Sr-90 from SRP and Hanford could supply the total 1 MW thermal requirement (150 MCi at $1 to $3 per Ci) at costs in the range of $150 to $450 per watt

[en] An ultrasonic technique developed at Mound to nondestructively inspect an assembly weld critical to the fabrication and production of MC2893 heat sources is described. Prior to transferring the assembly technology to Los Alamos National Laboratory (LANL), the ultrasonic technique was used at Mound as a 100% in-line inspection tool

[en] This technical monthly report covers studies related to the use of ²³⁸PuO₂ in radioisotope power systems. Most of the studies discussed here are ongoing. Results and conclusions described may change as the work continues

[en] The second in a series of quarterly reports for Technology and Space Applications materials programs conducted by the Metals and Ceramics Division of Oak Ridge National Laboratory for the Nuclear Research and Applications Division of ERDA is presented. These quarterly reports replace the monthly and annual reports previously issued on this work. The areas of research covered include high-temperature alloys for space isotopic heat sources, physical and mechanical metallurgy of heat source containment materials, isotope Brayton system materials support, and space nuclear flight systems hardware

[en] The micro-watt thermoelectric generator, e.g. for a cardiac pacemaker, consists essentially of two subassemblies. One subassembly contains an outer casing and an arrangement of insulating foils between the casing and a core casing with a getter of barium pellets. The other subassemby is made up of the fuel capsule with Pu-oxide, a thermopile arrangement of semiconductor material like Bi₂Te₃, Sb₂Te₃, Bi₂Se₃ and mixtures thereof, as well as a base plate. This subassemby is highly vacuum-tightly sealed against the outer casing by means of a terminal plate. The terminal plate consists of niobium, tantalum, or a tantalum alloy. A ring-shaped plug of aluminium oxide is inserted in it through which an electric connection consisting of niobium is tightly conducted. The inner and outer surface of the plug are alloyed with molymanganese. By brazing with silver-copper or gold-copper, the niobium parts are connected with the aluminium oxide plug. (DG)

No abstract available