EFFET DOPPLER LIé à LA TEMPéRATURE DE COMBUSTIBLE DANS UN RéACTEUR CANDU

摘要

The variations of the nuclear fuel temperature and density of coolant in a CANDU reactor can have an important effect on its reactivity. Cell and reactor simulations have been made using the DRAGON and DONJON softwares. Cell calculations enabled us to observe a drop in reactivity along with the increase of fuel temperature. A fall in the density of the coolant results in an increase of reactivity in the cell. These effects are present throughout the isotopic evolution of fuel, but become less important as time advances. Disturbance calculations enable us to observe that the effect of an instantaneous change of fuel temperature during the evolution is not the same at the beginning and at the end of the evolution. Indeed, one finds a point of inversion on the evolution curve where the disturbance does not have any effect. On both sides of this point, the effect of disturbance is of opposite sign. This phenomenon of inversion, considered in a reactor calculation, explains why an instantaneous change of the fuel temperature in a reactor, which has a distribution of fuel age, is almost null.