Etudes en cours à l'IPSN sur les lois de dilution.
J. Anno, 6éme conférence internationale sur la criticité-ICNC'99, 20-24 septembre 1999, Versaille, France.
Criticality calculations need, as input data, the atomic densities of fissile materials. Dilution laws determine them. At a given temperature, for a fissile material in aqueous solution, these laws connect the density of fissile mixtures with the concentrations of the fissile elements and the acidity of the mixture.
The paper presents the IPSN comparative study on these laws, especially experimental ones, on oxyfluoride and nitrate, which are responsible of different results for characteristics such as Keff, critical masses. Benchmarks can be used to validate these laws, and benchmarks Keff values versus formula are presented. Sometimes, results are not conservative, which shows us the necessity to have appropriate safety margins and safety coefficients to define safe values.