The critical models are very low-power reactors (a few hundred Watt) used to obtain precise neutronic data on the fission reaction.

To obtain this data, neutronic experiments are conducted in the three reactors called Éole, Minerve and Masurca which simulate various types of industrial reactor cores:

• Éole is used for cores for thermal neutron and pressurised water (PWR) or boiling water (BWR) reactors. Design codes of the Japanese BWRs are in the process of qualification, at the request of JNES

• Minerve is primarily used to measure cross sections of core component materials

• Cores for sodium or gas Fast Neutons Reactors are tested on Masurca, which is also used to study minor actinide transmutation, in response to the 1991 law on management of high activity long-life nuclear waste.