The vapor pressure of plutonium dioxide (PuO2) was investigated in the range 1450° to 1775°C in air, argon, and oxygen atmospheres by a transpiration technique. There were strong indications that PuO2 can vaporize congruently or as a suboxide species, depending on the atmosphere. The δH°298 for vaporization in 1 atm of oxygen is approximately 154,000 cal per mole. The estimated standard free energy of formation (δG°f) of gaseous PuO2 is −121,000 + 10.7 T from 1227° to 1827°C.

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This is the third in a series of quarterly reports describing the results of several experimental programs being conducted at Battelle-Columbus to develop components for advanced radioisotope heat source applications. The heat sources will for the most part be used in advanced static and dynamic power conversion systems. These reports replace the informal monthly technical letter reports previously prepared and are being utilized so that more cohesive presentation of results can be achieved. In addition^ a series of sumnary management monthly reports was initiated in July of 1976 to permit NBA assessment of contractual progress. Previous quarterly reports are identified as BMI-X-672 October 1976^ and BMI-X-676 January 1977. The activities covered in this new series of reports are conducted under Contract No. W-7405-eng-92j Task 94. The specific components development efforts which are described herein are: improved selective and nonselective vents for helium release from the fuel containment; an improved reentry member and an improved impact member^ singly and combined. The unitized reentry-impact member (RIM) is under development to be used as a bifunotional ablator. Finally^ thermochemical supporting studies are reported.

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