Thermal-hydraulic simulation for normal operation of the Dalat nuclear research reactor

Abstract

A mathematical model has been developed for the Dalat Nuclear Research Reactor (DNRR, Vietnam) to study its thermal-hydraulic dynamics. The point kinetics equations with reactivity feedback mechanism are used to predict the changes in neutron power. The reactor hydraulic network is represented by a node-link circuit. Conservation equations are applied to write the lumped parameters for each node and link. The rate method for the equation of state is implemented to calculate water thermodynamic properties. Numerical solutions in implicit scheme are formulated and coded. The coupled point kinetics and thermal-hydraulics code has been established to simulate the dynamic behaviour of the thermal-hydraulic parameters for normal operations of the reactor. With the known neutronic data and the reasonable validation of empirical correlations, most parameters such as power, core flow, coolant and fuel temperatures are obtained dynamically. The results obtained compare well with the practical observations. The hot channel calculations give maximum fuel surface temperature as well as the margins to the onset of, and departure from, nucleate boiling, which are important in reactor safety analysis. By using the code, several postulated reactivity transients have been investigated with the safety limit set at the onset of nucleate boiling. Although the void formation due to boiling is not covered, the safety analysis of the reactor is conservative.