Method of adaptive nodes for coarse-node computations

The analysis with the COMMIX program of liquid-metal reactor intermediate heat exchanger (IHX) transients that are characterized by low flows, and especially imbalanced low flows, shows that if a coarse-node structure is used, the predicted temperatures are significantly different than those given by a fine-node structure. If a fine-node structure is used, for problems that involve a large part of the plant, the computation time becomes excessive. In these IHX problems, high-temperature gradients develop along a very short length at one end of the exchanger, and the temperature distribution is practically flat in the remaining length of the unit. For a general-purpose thermal-hydraulic code like COMMIX, a method of general applicability is desirable. This paper presents a method of adaptive node structure that is based on general principles and gives an accurate solution with a few nodes. At this stage it has been applied only to one-dimensional problems. Its application to two and three dimensions is expected to be straightforward