Void Reactivity Response in Boiling Water Reactors

Abstract

In order to analyze void reactivity response caused by disturbances of inlet water velocity, inlet water temperature, system pressure and reactor power, the “Void Equation” is derived from the fundamental equations of mass and energy conservation and the assumption of “Slip Ratio”. This Void Equation is expressed as ∂f/∂t+U∂f/∂z=q where f: void volume fraction, t: time, z: length along a channel, U: “void transmission velocity” and q: effective heat source including the effect of system pressure change. “Negative Void” is introduced to treat reactivity response caused by water temperature change in the subcooled region in the same manner as in the boiling region. This void equation is applied to analyze kinetic behavior of a typical power reactor and its numerical solution is obtained with HIPAC-101 (Hitachi Parametron Digital Computer) and IBM-650. The linearized void equation is also derived and the void reactivity response diagram is obtained instead of the ordinary one using the “void map”.