Steady State Thermal Performance of a High Temperature Reactor Fuel Element

Abstract

The safe and economic operation of a nuclear reactor is highly dependent upon the detailed knowledge of the steady state thermal and hydraulic characteristics of the fuel. Various designs of HTR fuel element are discussed and the Tubular Interacting concept is described in more detail. This design, the one adopted for the Oldbury 'B' tender, was the one on which the analytical methods, described in this thesis, were based. The spatial and time distributions of heat generation, and fast neutron dose, are discussed and methods described which have been developed to determine spatial and time distributions of channel mass flow rate and coolant outlet temperature. With these distributions as boundary conditions, methods (involving the use of computer programs) are described which analyse the thermal performance of a fuel element. Particular emphasis has been given to three important aspects of fuel behaviour. The heat transfer and pressure drop characteristics of the coolant passages are investigated analytically. Dimensional change caused by thermal and irradition effects has a marked effect upon fuel element temperatures and this phenomenon is studied in some depth: Methods have also been developed which postulate the form and development of corrosive attack of the fuel channel and determine the thermal and hydraulic effects of such corrosion. Using all these methods detailed spatial and time dependent temperature distributions are determined for a single fuel element. Spatial distributions of peak fuel channel temperatures at a particular moment in the reactor core life (Snapshot) are also determined and, by making certain statistical observations, expected frequency distributions are found.