Distribution coefficient codes

To evaluate fission product release in a reactor, it is necessary to supply the appropriate particle geometry, diffusion coefficients, and distribution coefficients. This is a formidable task. To approach this problem, postirradiation fission product release has been studied as a function of temperature. The results of these studies are complex and require considerable interpretation. The SLIDER code without a source term has proved to be of considerable value in this interpretation. Parametric studies have been made of the integrated release of fission products, initially wholly in the fueled region, as a function of the diffusion coefficients and the distribution coefficients. These studies have led to observations of critical features in describing integrated fission product releases. From experimental values associated with these critical features, it is possible to evaluate at least partially diffusion coefficients and distribution coefficients. These experimental values may then be put back into SLIDER with appropriate birth and decay rates to evaluate inreactor particle fission product releases. Figure 11 is a representation of SLIDER simulation of a simplified postirradiation fission product release experiment. Calculations have been made with the following pertinent input data ... 

The distribution coefficients also change with time and space due to chemical reaction progress. Although transport codes can be modified to assign spatially variable K values, the variation with time cannot be set a priori. 

Figure 10.13 Distribution coefficient of uranyl nitrate between 30 v/o TBP in hydrocarbon diluent and aqueous nitric acid at 40°C, from SEPHIS code.

In the SEPHIS code [W5] this distribution coefficient ratio DpJD j is evaluated from... 

Figure 10.17 Distribution coefficient ratio, tetravalent plutonium to hexavalent uranium in 30 v/o TBP, from SEPHIS code.

VI] for equilibria at 30°C. Distribution coefficients agree with measurements of Siddall [S13] and Weinberger et al. [W6] except for thorium at aqueous concentrations below 0.06 Af within the dashed line, where the code predicts lower values than observed. 

The clay ion-exchange model assumes that the interactions of the various cations in any one clay type can be generalized and that the amount of exchange will be determined by the empirically determined cation-exchange capacity (CEC) of the clays in the injection zone. The aqueous-phase activity coefficients of the cations can be determined from a distribution-of-species code. The clay-phase activity coefficients are derived by assuming that the clay phase behaves as a regular solution and by applying conventional solution theory to the experimental equilibrium data in the literature.1 2 3... 

In the kinetic neutral particle transport codes (such as DEGAS, EIRENE, etc.), besides the cross-section (or rate coefficient) information on atomic collision processes, information on energy and angular distribution of reaction products is also required. We have omitted this aspect in our discussions of... 

The similarity between two structures is calculated by means of an associated coefficient, usually the Tanimoto coefficient. Valence angles are 2D, and interatomic distances are ID. Most of the 3D searches of data bases have concentrated on interatomic distance information, e.g., hash codes for all distinct triplets of nonhydrogen atoms in pairs of isomeric structures. If one uses frequency distributions instead of hash codes, one can also compare nonisomeric molecules. 

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