Reactor operating process and spectral shift reactor using this process

This light water reactor uses transplutonium elements incorporated in fuel rods to alter the neutron energy spectrum during its fuel cycle. In a first phase the rods are introduced in the core when its reactivity is high and it is necessary to reduce the moderator ratio and hence to reduce the number of thermal neutrons by increasing the number of epithermal neutrons. In a second phase when the reactivity is lower the fuel rods are withdrawn above the reactor