NUCLEAR-DEBRIS FORMATION 35 provide both direct input information for the thermodynamic model and knowledge of molten-soil chemistry which allows extension to many soil types. The information required by the model is the number of moles nf of volatile constituent in the vapor phase and the number of moles n, in the condensed phase at equilibrium. To makethis ratio invariant to the relative quantities of each phase, it is customary and convenient to express the partition in terms of concentrations, e.g., the mole fractions in either phase (N, = n,/=n,), concentration in the gas phas- (c?=n?/V), or concentration in the condensed phase (c; = n;/M). Here V refers to the volume of vapor and M to the mass of condensate. Partitions can then be expressed in terms of Henry’s law: cy N, ky R where k, is Henry’s law constant, R is the molar gas constant, and T is the absolute temperature, or in various forms of a distribution coefficient, such as Ay = cf/c, AY = ch /N, Ay = NY/N, Henry’s law expression is applicable only if the species of volatile material in the vapor state is known (monomer, dimer, degree of dissociation, degree of hydration, etc.), whereas \, and Aj are applicable under all circumstances of present interest. It is appropriate at this point to raise a number of questions about the sensitivity of the distribution coefficients to several environmental variables: How will they be affected by (1) various soil compositions, (2) the presence of volatile material in the soil, (3) the concentration level of the active species, (4) the presence of moisture, and (5) the temperature? We have not tried to answer all questions at once, only the first three. The studies have been concerned with the basic oxide, Rb,O (precursor of strontium radionuclides), and the acidic oxide MoO, (precursor of ruthenium radionuclides). The results here include some obtained for the Division of Research, AEC. Soil Composition Soil compositions vary over wide ranges, but usually they are composed of a relatively small number of major constituents, both refractory (SiO,, Al,0;, Fe,O;, FeO, MgO, and CaO) and volatile (Na,O,