AbstractStatic calculations using the computer code LEOPARD have been used to investigate the effect of fuel rod motion on neutron-density noise during core burnup of a pressurized water reactor (PWR). These calculations show a variation with burnup in agreement with the experiment and give approximate quantitative agreement with the experiment for the root-mean-square value of the noise for reasonable assumed values of fuel rod motion. It is suggested, therefore, that fuel rod motion is a likely source of neutron-density noise in a PWR.