Study of the reactivity effect of bubble collapse in molten liquid metal cooled reactors

The reactivity effect of void collapse on a Core Disruptive Accident in a sodium free fast reactor core was studied. A two-dimensional transport theory computer code was employed to obtain a reactivity model which incorporated random distributions of voids in spatial location and bubble size. This model was implemented into VENUS-II and several excursions were investigated for the purpose of assessing the effect of bubble collapse reactivity on excursion energy. In addition, comparisons were made between the VENUS-II results obtained using the transport reactivity model and those obtained using a reactivity model developed from the Behrens' formulation of the leakage effects due to the presence of bubbles. The results indicate that excursion energy is sensitive to the shape of the reactivity versus void fraction function and that reactivity models based strictly on leakage effects are probably conservative compared to models which include both self-multiplication and leakage