Finite-element analysis of two-phase flows

Safety studies for liquid cooled reactors address the questions raised by postulated failures on the cooling system. It is of importance to predict the time history of the depresurization that follows a loss of coolant accident to guarantee the integrity of the overall system. In this report the sudden depressurization of a straight pipe filled with heated and compressed water is investigated. This condition is isolated from a complicated sequence of events triggered by a loss of coolant in a water cooled reactor. The investigated water column contained in a straight section of pipe is released suddenly at one end. After a quick initial pressure drop, vaporization occurs. At this point, the rate of depressurization becomes much lower. The pressure inside the pipe is now controlled by the rate at which the steamwater mixture escapes through the open end. Previous analytical investigations used the fluid dynamics equations for conservation of mass, momentum and equilibrium. The resulting differential equations in time were solved by means of finite-difference operators. This investigation represents the first attempt to employ a direct stiffness finite-element approach to the solution of the depressurization of a straight pipe. The MARC Nonlinear Finite Element Analysis program provided the necessary software capabilities. (Auth.)