Simplified formulae of estimation of the number of fissions for criticality accidents with powders or configuration with rods in water - 6-03

This article presents simplified formulae for the estimation of the number of fissions for criticality accident with powders or configurations with rods in water. These formulae are the adaptation of a previous formula initially developed for criticality accidents occurring within fissile solutions. These formulae are based on the 'heat energy formula' from the first law of thermodynamics. Furthermore, adiabatic conditions, no recondensation of the solution during boiling and a constant pressure are assumed. Thus, for criticality accident in solutions, the number of fissions in this model corresponds to the energy given by the addition of the energy required to bring the solution to the boiling state and, in case of boiling of the solution, the energy required to evaporate a mass of solution. These formulae are presented with practical applications for UO₂ powders and UO₂ PWR rods. The suggested formulae lead to a bounding estimation of the number of fissions for the first moments of the criticality accident, until the heat loss becomes a predominant phenomenon