EPEE: a tool to compare the moderating efficiency of a material to the one of water
Résumé
To carry out the criticality safety assessment of a nuclear facility or a process, it is necessary to distinguish not only the fissile materials which are handled inside, but also the non-fissile materials which may be close or even mixed with the fissile material. These non-fissile materials can moderate/slow down and thermalize the neutrons and thus increase the neutron production rate within the fissile material: they are referred to as “moderating materials”. This is particularly the case for non-fissile materials containing light nuclei such as hydrogen (and its isotopes) and, to a lesser extent, carbon (e.g. water, oils, polymers, solvents, lubricants, fire-extinguishing powders, etc.).
Criticality safety assessments usually take into account water as moderating material. Although there are materials with better moderating efficiency (e.g. high-density (0.96) polyethylene), water is indeed the historical moderator as its hydrogen mass content makes it a conservative moderator in many configurations. The moderating efficiency of a material, compared with water, depends on its composition and its density.
This paper presents a new approach to predict if a moderating material is covered by water when criticality safety is ensured by mass control, at optimal moderation. This methodology is based on criticality calculations performed using the APOLLO2-Sn route of CRISTAL V2.0. The approach involves simulating different non-fissile fictitious materials, with varying hydrogen, carbon and oxygen contents as well as density, and comparing them to water in terms of moderating efficiency for mass control, at optimal moderation. Elementary validation data are also presented by testing a large number of real moderating materials.
In addition, a user-friendly tool named “EPEE” has been developed to implement this methodology by entering either its density and molecular formula or the mass concentrations of its constituent elements.
Domaines
Physique [physics]
Origine : Fichiers produits par l'(les) auteur(s)