Means for stopping a criticality accident in the MELOX homogenizer

摘要

The purpose of this paper is, starting from the criticality event scenario in the homogenizing workstation, to define the impact of different neutronic absorbers and determine the most effective one to stop the chain reaction. At least 14 litres of water are necessary for a chain reaction to occur in the MELOX homogenizer if the fissile medium and the water are heterogeneously distributed. However, if all the matter is homogeneously distributed, the accident cannot last if there is less than 59 litres of water. The first way to stop a criticality accident in the homogenizer is thus to homogenize the content of the tank. If more than 59 liters have been poured in the homogenizer, then the use of neutronic absorbers like boron or gadolinium is necessary. The absorbers can be either liquid or solid. The study shows that liquid absorbers aren't efficient enough because of their strong moderator effect. Then a study has been performed with a solid absorber: the gadolinium oxide. It is shown that less than 250 g of Gd is enough to stop a criticality accident in the homogenizer.