Effects of Fission Products on Physical Quantities Accompanying Burn-Up of Large Pu-U Fast Reactors

Abstract

The effects brought by the presence of fission products (F.P.) on the effective multiplication factor k eff, the Na-void reactivity, the breeding ratio, the fuel composition and kinetics parameters have been calculated as functions of burn-up for Pu-U fast reactor with 3,000l core volume. The F.P. sharply reduce k eff and increase the positive values of the Na-void reactivity. Moreover, at a given burn-up, this effect of F.P. on k eff and Na-void reactivity is governed largely by the total amount of the F.P. found accumulated at the time of observation, and is independent of the history of the material. The F.P. hardly influence the transformation accompanying burn-up undergone by the ratio of Pu to 238U atoms and by the isotopic composition of Pu. Similarly, the effect on the internal breeding ratio also is very small. The total breeding ratio increases gradually with accumulation of the F.P. The effect on the effective delayed neutron fraction βeff is only slight, while that on the prompt-neutron lifetime l p is appreciably larger.