A NEW LUMPED THERMAL RESISTANCE HEAT TRANSFER MODEL FOR FUEL PIN STRUCTURE

摘要

Lumped parameter heat transfer methodology is simple, and the solution is very fast, so the lumped parameter approach has been widely used in the thermal-hydraulic analysis for the fuel pin heat transfer in the nuclear reactors. In the conventional lumped parameter thermal analysis of the fuel pin structure, each component (suchas pellet, cladding etc.) is characterized by a concentrated bulk temperature (or averaged temperature), and a bulk thermal resistance. In contrast to this conventional lumped thermal resistance model, in this paper another kind of lumped thermal resistance heat transfer model for fuel pin structure has been developed. In this model, each fuel pin component is still represented by a concentrated lumped mean temperature, while the location of the mean temperature position of each component is no longer set on the geometrical middle point, rather exactly assigned on the analytical temperature profile. Two thermal resistance elements are assigned for each component in this new model: between each component outer surface and lumped mean temperature node a thermal resistance is assigned, respectively, each lumped thermal resistance connects the mean temperature node with the corresponding outer surface. The heat conduction between mean temperature nodes of different components is properly defined to takes place at the in-between surfaces. Within this new model, the location of the mean temperature positions for each component can be determined analytically, and all the thermal resistances are re-defined, accordingly. The advantage of the presented method is that the temperature profile in the fuel structure at any radial position can be re-produced after a quite easily lumped heat transfer calculation. This methodology can be used in nuclear reactor simulation studies where fastness of the solution is a matter of concern, meanwhile the exact temperature profile in the fuel pin structure can be re-produced at the same time.