The release of chemical species during core debris-concrete interactions

Under certain hypothetical PWR severe accident conditions, the release of radionuclides from molten core debris undergoing thermochemical interaction with the basemat concrete is potentially an important contributor to the source term. The authors have previously shown that in some circumstances the mass transfer rates involved are sufficiently rapid to make them unimportant. In a subsequent paper it was shown that the magnitude of the release is very sensitive to the degree of mixing or layering of the melt, to the temperature of the melt and to the compositions of the melt and the concrete. The detailed study of the chemistry of the interaction is continued in this paper with consideration being given to the thermodynamic data, to various approaches for the calculation of chemical equilibria and to the speciation of the released material. In addition, the effect of the heat transfer rates on the approach to thermochemical equilibrium is investigated