New estimation method for void reactivity coefficient using the TRACY transient data

Ogawa, Kazuhiko ; Kaminaga, Fumito*

In the safety research regarding a criticality accident in nuclear reprocessing plants, prediction of nuclear fission yields is essential to evaluate its influence on a radiation of neutrons/-rays to the public. For numerical calculations of the number of fissions in a criticality accident, a void reactivity coefficient due to the formation of radiolytic gas voids in the solution is required to evaluate the negative feedback reactivity. Small oscillations of both the power and the core pressure are measured after the first power pulse in a slow transient operation in TRACY. The small power oscillations are due to the reactivity feedback effect of the change of the volume of gas voids. In this paper, we propose a new estimation method of the void reactivity coefficient and estimate the coefficient using the TRACY transient data. The present estimated void reactivity coefficient is less than the calculated values in the uniform distribution of gas voids.