Parametric effects on coupled neutronic-thermohydraulic stability characteristics of supercritical water cooled reactor

- Lumped parameter model is proposed for stability analysis of SCWR.
- Effect of both thermal hydraulics and neutronics is studied.
- Linear and transient stability maps show qualitative agreement with RELAP5.
- Effects of pressure, orifice coefficients, diameter and heated length are studied.
- Effects of fuel time constant and enthalpy reactivity constant are studied.

Supercritical Water-Cooled Reactor (SCWR) is one of the advanced reactor types under Generation IV program. Similar to BWR, there are large changes in thermodynamic properties of the coolant in SCWR, but its dynamic characteristics are different from existing reactors due to the supercritical conditions of the coolant. This necessitates study of the stability behaviour of SCWR, which requires a dynamic model of the reactor. A simple unsteady lumped parameter model (LPM) for coupled neutronic-thermohydraulic transients in SCWR has been developed in this paper. The LPM includes point reactor kinetics for neutron balance and a two region model for fuel and coolant thermal hydraulics. The two regions considered in the model are separated from each other by a boundary that depends on the pseudocritical temperature of the coolant. The results of dynamic simulation and linear stability analysis are shown by plotting stability maps. These results show good agreement with each other. Furthermore, to study the effect of parameters on the stability of the system, variations of some geometric, control and neutronics parameters are studied. The stability maps predicted by the LPM are also compared with those obtained with RELAP5 code, and are found to show similar trends.