Control system design for a pressure-tube-type supercritical water-cooled nuclear reactor via a higher order sliding mode method

Nuclear power plants exhibit non-linear and time-variable dynamics.Therefore,designing a control system that sets the reactor power and forces it to follow the desired load is complicated.A supercritical water reactor(SCWR)is a fourth-generation conceptual reactor.In an SCWR,the non-linear dynamics of the reactor require a controller capable of control-ling the nonlinearities.In this study,a pressure-tube-type SCWR was controlled during reactor power maneuvering with a higher order sliding mode,and the reactor outgoing steam temperature and pressure were controlled simultaneously.In an SCWR,the temperature,pressure,and power must be maintained at a setpoint(desired value)during power maneuvering.Reactor point kinetics equations with three groups of delayed neutrons were used in the simulation.Higher-order and classic sliding mode controllers were separately manufactured to control the plant and were compared with the PI controllers speci-fied in previous studies.The controlled parameters were reactor power,steam temperature,and pressure.Notably,for these parameters,the PI controller had certain instabilities in the presence of disturbances.The classic sliding mode controller had a higher accuracy and stability;however its main drawback was the chattering phenomenon.HOSMC was highly accurate and stable and had a small computational cost.In reality,it followed the desired values without oscillations and chattering.

Corrosion of candidate materials for supercritical water-cooled reactor

Supercritical water reactor(SCWR) was proposed as a GenerationⅣconcept for building large capacity nuclear power plants.Comparing with the present GenerationⅡandⅢlight water reactors,SCWR possesses great advantages of 10%higher efficiency,simpler system design,better sustainability,and so on. However,the selection of materials for fuel cladding and reactor internals of SCWR is facing a great challenge. Corrosion in supercritical steam is of the first important issue to be solved to meet the stringent requirement of the reactor internal components.Corrosion screening tests were conducted on candidate materials for nuclear fuel cladding and reactor internals of supercritical water reactor(SCWR) in static and re-circulating autoclave at the temperatures of 550,600 and 650℃,pressure of about 25 MPa,deaerated or saturated dissolved hydrogen(STP). Nickel base alloy type Hastelloy C276,austenitic stainless steels type 304NG,AL-6XN,HR3C.NF709 and SAVE 25,ferritic/martensitic(F/M) steel type P92,P122 and 410,and oxide dispersion strengthened steel MA 956,are tested.This paper presents corrosion rate,and focuses on the formation and breakdown of corrosion oxide film,and proposes the future trend for the development of SCWR internal structure materials.

Numerical investigation on cold flow dynamics of supercritical water fluidized bed reactor with inclined distributor: Design and scale up

Supercritical water fuidized bed reactor(SCWFBR)is a novel concept for the gasification of coal and biomass to produce hydrogen.In this work,to enhance the mixing in the axial direction,an inclined distributor is introduced to optimize the flow dynamics in SCWFBR with partitioned fluid supply.Through numerical simulations based on the two fluid model(TFM),the effects of the inclined distributor structure and operating parameters on the solid distribution and the residence time are evaluated with the optimal values determined.Numerical results show that,area ratio-2:1,scw velocity ratio-3:1,flow ratio=3.36:1 and inclination angle=20°are the optimal design in this paper.A predictive correlation of the minimum fluidization velocity for the improved SCWFBR is also proposed based on the numerical data.The average error between the correlation and numerical simulation results is approximately 1.4%which strongly demonstrates its capability.Finally,based on the optimal design,the labscale reactoris further scaled up and the studies about twoscale-uprules are carried out.Only the cold flow is simulated in this study without considering chemical reaction which would be involved in future work.

Effect of Heat Treatment Process on Mechanical Properties and Microstructure of Modified CNS-ⅡF/M Steel

Ferritic/martensitic（F/M） steels have been recommended as one of the candidate materials for supercritical water cooled reactor（SCWR） in-core components use for its high thermal conductivity,low thermal expansion coefficient and inherently good dimensional stability under irradiation condition in comparison to austenitic steel.CNS-Ⅱ F/M steel which has good mechanical properties was one of the 9-12Cr F/M steels designed for SCWR in the previous work.In this study a modified CNS-Ⅱ F/M steel was used and it＇s ultimate tensile strength was 925 MPa at room temperature and 483 MPa at 600 ℃ after optimizing heat treatment parameter.The ductile to brittle transition temperature of modified CNS-Ⅱ F/M steel is-55 ℃.Those are at the same level or even higher than that of CNS-Ⅱ and some commercial F/M steels nominated for SCWR in-core component use.The transmission electron microscope（TEM） results showed that the mechanical properties of the tempered martensite was closely related to the decomposition stage of the martensite.