Simulation of IAEA Reactivity Initiated Transient Benchmarks Using Reactor Dynamics Code “REDAC”

Abstract

This paper presents the analysis of reactivity initiated transients in an idealized, light water research reactor as a part of International Atomic Energy Agency (IAEA) safety related benchmark. The simulation model is based on point reactor kinetics coupled with one-dimensional (1D), two-channel model for thermal hydraulics. The point kinetics equations (PKEs) have been solved using an implicit Runge–Kutta (RK) method and the coolant transport equations have been solved using implicit finite difference formulation. Accuracy of the implemented models and methods has been demonstrated. Important safety parameters like peak power, peak fuel, and coolant temperatures have been predicted for a series of transients. Intercode comparison shows that the predictions of the present simulations are in good agreement with other codes. This approach provides a time efficient solution for safety analysis of reactors with tightly coupled core where point kinetics can be applied. To address the sensitivity of predictions with respect to important input parameters, simulations have been carried out with different sets of inputs reported in the literature. They indicate that predictions for fast transients are spread over a wider range compared to slow transients. For a given transient, predictions of peak power have a wider spread, while peak temperatures are relatively less sensitive to neutronic inputs. Also, for fast transients, prompt neutron generation time and delayed neutron fraction have dominant influence on the evolution of power. For slow transients, the reactivity feedback effects are equally important.