Letter to the Editor on the paper by W. Wulff, “Critical review of conservation equations for two-phase flow in the U.S. NRC TRACE Code”

The paper, “Critical Review of Conservation Equations for Two-Phase Flow in the U.S. NRC TRACE Code,” by W. Wulff is inaccurate and misleading. Modeling and simulation of two-phase flow is complex and uncertainties arise due to limitations in the state-of-the-art understanding of transport phenomena and the computational limits in modeling a nuclear plant. Global systems codes such as TRACE contain approximations and assumptions to simplify the conservation equations and arrive at a solution. The author’s paper suggests a misunderstanding of the approximations made to derive the expressions as programmed in TRACE. We believe the author’s critique to be largely invalid, as we document in some detail in this letter.