Study On Flow Stability Calculation Methods For Supercritical Water-cooled Reactor (SCWR)

The supercritical water-cooled reactor(SCWR)is one of the most promising generationIV nuclear reactor concepts,which is under intensive study because of the excellent heat transfer characteristics of water in the supercritical phase.CSR1000 is a Chinese supercritical water-cooled reactor,the preliminary design of which has largely been based on the theory of super light water reactor.Due to a greater availability of computational resources,experimental setups and maturity of analytical reasoning,there is a need to apply and review these methods/techniques on CSR1000 in order for vivid development to take place.This requirement holds a special significance,in that it covers various analysis methods and aspects of thermal hydraulic stability of the CSR1000 reactor core.More focus is required on the usage of computational methods and analytical reasoning in this topic.Many analysis methods have been devised in order to study the thermal hydraulic stability of supercritical water-cooled reactors;including analytical methods,computational fluid dynamics(using the k-? and k-? turbulence models),as well as numerical methods(using the response matrix method).The system response matrix method is a 1-dimensional analysis technique,in which the problem domain is discretized into a number of linear elements.The conservation differential(state)equations are solved alongside constitutive equations for each element,and the thermal hydraulic stability is represented by an array of decay ratios.The turbulence models can be applied using computational fluid dynamics(CFD)technique,in which the coolant channel is modeled(in 3-dimensions)and the conservation differential equations are solved with the help of additional turbulence equations.These methods reveal more information about the flow pattern of the coolant(during thermal hydraulic instability),but are far more computationally intensive.The results of this study suggest that CSR1000 operates within its stability bounds(decay ratio of 0.4191,below the operational safety limit of 0.5),when analyzed under its normal operating conditions.The stability of the system is sensitive to variation in its key operational parameters.CSR1000 comes at the verge of being unstable at 12 MPa(during the pressurization phase).Maximum power channel is more unstable as compared to average power channel.Pressure has opposing effects on the stability.An inlet orifice helps to stabilize the thermal hydraulic behavior in a passive way.Based on the temperature,there is 5% variation in the thermophysical properties of coolant 0.4 m from the outlet.A high degree of turbulence is observed in 1.5-2.0 m range of the coolant channel,as shown by secondary flow patterns.The stability results are also dependent upon the size of mesh.In summary,there are two advantages of using the system response matrix method and the CFD turbulence models for analyzing the thermal hydraulic instability in the CSR1000 reactor core.The system response matrix method is easier to implement,yielding results of dynamic analysis with a smaller computational time.The CFD k-? turbulence model gives more detailed information about the bulk flow pattern of the coolant(during thermal hydraulic instability).The CFD k-? turbulence model shows details about the instability near the wall of coolant.