Axial section of CROCUS represented using the Serpent2 code, with the addition of the PETALE metal reflector (top-left). The oxide uranium fuel is displayed in orange, the metal uranium fuel in red, and the water in blue. The four circles in the water reflector are fission and ionisation chambers used as CROCUS monitors. A zoom on the interface between CROCUS and the metal reflector shows the first foil with a width multiplied by 10 in order to be visible (1 g of indium for the first foil instead of 0.1 g).