The quantity and characteristics of fission products in coolant gases due to leaking fuel elements are discussed. It is concluded that the rare gases, the alkali metals, the halides, and Sb may act as permanent gases to a considerable extent. The other fission products are expected to condense out completely on walls or as dust consisting of metals, carbides, and oxides.

The maximum temperature in the interior of the fuel element could be greatly reduced by incorporating a liquid between the fuel element and the outer can to increase-heat transfer rates. It is of interest to consider what liquids would be chemically compatible with graphite and the actinide carbides. Elements which melt below 1100 and boil above 1400 deg C that form no stable solid carbides, include Cu, Ga, TI, Ge, Sn, Pb, Sb, Bi, and compounds include GeP, GeS, GaP, Ga/sub 2/S, GaTe, GaAs, SnTe, Sm/sub 3/As/sub 2/, Sb/sub 3/Te/sub 2/, Zn/sub 3/Sb/sub 2/, Zn/sub 3/P/sub 2/, ZnS, ZnTe, and Zn/s ub 3/As/sub 2/. Some of these compounds have equilibrium pressures that might be considered too high, but they may actually vaporize slowly enough because of low vaporization coefficients to make them suitable. There are probably rot enough data nor adequate theories for predicting the rates, and Langmuir type vaporization experiments would be necessary to determine the rates of vaporization of these compounds. The main problem in the use of a heat transfer fluid is that of reaction between the fluid and the actinide carbides. Thermodynamically extensive attack would be expected. However, it may be possible to make the rate …

From the point of view of constituents of a fuel element at temperatures between 2500 and 4500 degree K, the fuel elements can be considered to consist of six types of material: carbon, elements less volatile than carbon, 26 moles of rare gases, 21 moles of alkali metals, 17 moles of alkaline earth metals, and 4 moles of miscellaneous volatile elements. Various processes involving the constituents from 2000 to 45000 degree K are considered. Reactivity gain due to can rupture is discussed.