A finite element thermal hydraulic analysis of a plate type fuel element

Abstract

In this work a mathematical model and a Computer program developed to perform thermcohydraulic analysis of a plate type fueled, water cooled nuclear core is presented. A finite element numerical solution was obtained for the two dimensional heat conduction model developed. For the transient case, the finite difference method was chosen to approximate the time derivative. In the early stages of this work a lot of time and effort were necessary for the preparation and entering of the needed data for calculations. This difficulty was overcome later after using a grid generating subroutine. In the determination of coolant temperature and pressure change mass, energy and momentum balance equations were evaluated for a control volume. The computer program NEKA developed, throughout this work is used for the steady state calculations. If desired, subcooled boiling and transient calculations can also be performed using NEKA. In all cases the program may be used either interactively or using data file. Two sample reactor cores were analyzed for various operating conditions such as the steady state analysis for a given power level, transient analysis with the change of power, coolant inflmi temperature, inflowing mass flowrate as a function of time. In the lMW power generating core, the Reactor I in Çekmece Nükleer Araştırma ve Eğitim Merkezi, showed to have a maximum fuel temperature of 76.7°C under normal operatingoxditkms for 37°C coolant input temperature This temperature reached to ,66.8 °C if coolant enters at 23 °C. In the transient analysis, for a given step change 90 per cent of the total change was observed to complete within 5.2 seconds. In the case of Reactor II which produces 5MW, the maximum fuel tanperature reached to 69.2°C under normal operating conditions for 30°C coolant input temperature. If the coolant flowrate is decreased to 0.065 kg/s from 0.31 kg/s or power level is increased to 17.5 MW subcoo1ed boiling occurance was predicted. For both reactors, the operating conditions were found to be safe.