Some Aspects of Modelling CWIT Refill Test 1465 Using CATHENA

Abstract

CATHENA is a multipurpose thermahydraulic computer code which can be used for analysis of postulated LOCA scenarios for CANDU reactors. The CWIT refill test facility at Stem Laboratories, funded by the COG (CANDU Owners Group), has been used to investigate the flow and heat transfer behaviour as a function of channel power, system pressure, liquid subcooling, header injection flow rates, and channel configuration (Hanna and Mallory, 1989). The test No.1465 was one of the refill experiments using the CWIT facility to investigate the quench and refill behaviour of the feeders, end fittings and channel during some postulated LOCAs (Buell and Kowalski, 1994). This test simulated a symmetric inlet/outlet header 50 mm break size with near-zero header-to-header pressure drop. A CATHENA representation of the CWIT facility was developed. The paper emphasizes the modelling of some non-pipe components in the system. CA THENA provides the user many choices for modelling these system components. Different code components were applied for modelling the header and end fitting, and the refill transients were compared. The use of a solid-to-solid contact model, giving zigzag heat conduction along the wall was investigated, to study the impact of axial heat conduction on a moving quench front. Suggestions are offered for future applications of CATHENA to similar problems.