Thermal-hydraulic transient analysis of a packed particle bed reactor fuel element

Abstract

A model which describes the thermal-hydraulic behavior of a packed particle bed reactor fuel element is developed and compared to a reference standard. The model represents a step toward a thermal-hydraulic module for a real-time, autonomous reactor powder controller. The general configuration of the fuel element is a bed of small (diameter about 500 microns) fuel particles are packed between concentrically mounted retention cylinders referred to as frits. The momentum integral approach used in the MINET code is applied ot this model to balance the fundamental mass, energy and momentum conservation relationships. The element is divided into only three control volumes: the inlet plenum and cold frit define the first control volume, the fuel particle bed defines a second control volume, and the outlet plenum and hot frit define the third control volume. The solid phase of the particle bed is represented by a single node. This simple model was validated against the reference standard and compared favorably. As a demonstration of the model's flexibility, a number of variations were analyzed. These included variations in fuel element geometry and the initial and final values of inlet temperature, inlet pressure, and outlet pressure. As a final demonstration a cluster of nineteen, 1 meter long fuel elements, arranged to form a core, were analyzed for an up-power transient from 0 MWt to approximately 18 MWt. The simple model significantly decreases the time necessary to perform a single analysis. A transient of 10s with a timestep of 10 ms, for example, takes approximately 45s of computation on a desktop computer equipped with an 80386 microprocessor