NUCRIC Simulations of a CANDU-Type Header Manifold Model

Abstract

Site measured inlet and outlet header pressure measurements and ultrasonic feeder flow data, confirm the existence of axial pressure gradients along the inlet and outlet headers. These axial pressure gradients give rise to individual header-to-header pressure drops for each channel. A discretized form of the one-dimensional momentum equation, as derived by Bajura and Jones, was developed for use in NUCIRC to simulate the axial pressure gradients and flow distribution throughout both the inlet and outlet headers. The practical application of the model required adaptations to account for the inlet/outlet header geometry, feeder pipe distribution along the headers, the inlet header entrance conditions, and the midplane flow splits. Sensitivity analysis using an ideal header model is used to demonstrate the capabilities of the header manifold model for accurate header to header pressure drop determination for each individual channel. The effect of feeder attachment asymmetry, flow blockage, and header design is investigated. The results suggest that the model is quite robust and that the momentum correction factors (B and y) are a significant component of the header axial pressure gradient. The asymmetry in the feeder size, feeder length, and feeder attachment also play a role in defining the header axial pressure gradient but are not the dominant factor. The major contributor to the axial pressure gradient are the discharge flows into the inlet header.