CERIUM VISCOSITY MODELING ABOVE LIQUIDUS TEMPERATURE

In the event of a highly unlikely core melt-down accident in Pressuriz ed Water Reactors (PWR), scenarios in which the reactor pressure vesse l fails and the core melt mixture (called cerium) relocates into the r eactor cavity, cannot be excluded. The Nuclear Reactor Division (CEA/D RN) has undertaken investigations in order to model rheological cerium behaviour. In this paper, a bibliographic study and a comparison with available data lead to the conclusion that the viscosity of cerium co ntaining UO2, ZrO2 and Zr can be calculated, at the melting point, wit h a good accuracy using the Andrade formula. Above the liquidus temper ature, the correlations, proposed for pure metals and metal alloys, be tween the activation energy and the melting temperature are not availa ble in the case of urania and thus cannot be used to calculate liquid cerium activation energy. To overcome this problem, in this paper we p ropose to use a mole fraction averaged activation energy. Nevertheless , this last point needs to be validated, (C) 1997 Elsevier Science S.A .