Development of Governing Equations Based on Six Fields for the RELAP Code

The RELAP5-3D code is used to analyze nuclear reactor systems during steady-state and transient operations. Reactor transients that result in significant two-phase flow conditions and phase change, such as reflood scenarios, loss-of-coolant accidents, and others, can tax the current capabilities of the code to model the flow fields. Current codes, such as RELAP5-3D, RELAP-7, and TRACE, have mass, momentum, and energy governing equations for only two fields (liquid and vapor). The representation of two-phase flow phenomena is improved by increasing the number of fields. Therefore, governing equations based on six fields (liquid, vapor, small bubble, large bubble, small droplet, and large droplet) are derived in this paper for implementation in RELAP5-3D.