Analysis of RD-14M Two-Phase Thermosyphoning Experiments and Associated CATHENA Simulation Results

Abstract

This paper presents some of the results of a detailed analysis of some of the two-phase themosyphoning tests conducted in the RD-14M multiple channel figure-of-eight loop test facility. The tests were conducted to obtain a better understanding of two- phase thermosyphoning behaviour in a multiple-channel facility. The tests generally showed similar thermohydraulics phenomena as the loop inventory was reduced. There is a basic difference between two-phase thermosyphoning behaviour in the tests conducted in the multiple- channel RD-14M and in the previous RD-14 single-channel per pass loop test facilities. In each of the RD-14M tests, the flow in some of the channels in each pass reversed direction and this new direction was sustained for a long time. This reversal generally was not observed in the tests conducted in the single-channel test facilities. This reversal played an important role in the subsequent RD-14M loop thermohydraulics behaviour. Specifically, the channel flow reversal reduced and in some tests stopped the thermosyphoning flow and caused the loop pressure to rise. The flow reversal and subsequent loop inventory draining8 eventually caused the flow in some channels to decrease and stratify resulting in channel heatup. The report presents a physical interpretation for each of the major phenomena observed in the tests. A simple criterion for the onset of channel flow reversal similar to that proposed previously is given. CATHENA was used to simulate a number of the RD-14M tests with the objective of obtaining a better understanding of the phenomena observed in the tests. CATHENA generally predicted all of the observed phenomena. The details of the predicted results depended on the choice of the steady state conditions and heat loss distribution around the loop. The paper also studies the results of the CATHENA simulations of the tests to support the interpretation of the test results.