Research And Application Of High Temperature Creep Theory Model And Numerical Simulation For UNS N10003 Alloy

Creep-fatigue and creep buckling instability are the main failure modes of reactor pressure vessel(RPV)in Thorium Molten Salt Reactor(TMSR).The elastic or inelastic methods are proposed to analysis and evaluate these two failure modes in the high temperature nuclear design codes(such as ASME-NH).The creep effect is remarkable for the key parts(such as the nozzle region)of the RPV in TMSR and the stress level also exceeds the limit of the elastic analysis criterion,thus the inelastic creep-fatigue damage analysis is needed.In addition,the inelastic creep buckling analysis is required for the buckling-instability evaluation of the high temperature structure.However,there are still some problems existing in the creep-fatigue damage and creep-buckling analysis with the inelastic analysis method for the RPV in TMSR at present.On one hand,there is a lack of the research on creep damage and creep-fatigue damage theory models for the Ni-based UNS N10003 alloy,which is the key structural material of the RPV in TMSR.On the other hand,the numerical simulation technology about creep damage and creep buckling has not been well developed.All these bring great difficulties and challenges to the high temperature structural integrity assessment of the RPV in TMSR.Based on the theory of continuous damage mechanics,an inelastic creep damage model of high-temperature Nickel-based UNS N10003 alloy is established and its numerical simulation technology is also developed.Then an inelastic multiaxial creep-fatigue damage model of the alloy is studied,and the sensitivity analysis of parameters and the comparison of life prediction models are carried out.Besides,the numerical calculation methods about creep buckling of long cylindrical shells are discussed based on the creep damage models.Finally,the inelastic creep damage and creep-fatigue damage analysis,as well as creep buckling analysis of the RPV in TMSR are carried out by using the above theoretical models and numerical calculation method.The main conclusions of this paper are as follows:(1)The Norton creep model and K-R creep damage model of UNS N10003 alloy at 650? are obtained.The analysis results show that the K-R model is more suitable for describing the creep damage behavior of UNS N10003 alloy.A modified K-R creep damage model is proposed,which has higher accuracy than the original K-R model.The UMAT subroutine is customized,which can simulate the modified K-R model in ABAQUS software effectively.The finite element analysis results agree well with the theoretical values with good numerical convergence.(2)The Lemaitre multiaxial creep-fatigue damage model is obtained for UNS N10003 alloy at 650?.The theoretical predicted values of creep-fatigue damage are more conservative than experimental data.Three factors,such as the stress triaxial ratio,Poisson's ratio and the number of cycles in the life cycle,have influence on the theoretical prediction results of creep-fatigue damage,among which the stress triaxial ratio is the most sensitive.(3)The numerical results of creep buckling show that the modified K-R creep damage model can accurately simulate the long-term creep buckling behavior of the long cylindrical shells.Isochronic stress-strain method can be used as a simplified creep buckling analysis method,and its numerical solution is more conservative.The critical creep buckling loads are sensitive to the ratio of diameter to thickness,geometric deviation,energy dissipation fraction,mesh density and boundary constraints.(4)The inelastic creep damage and creep-fatigue damage,as well as creep-buckling of the RPV in Thorium Molten Salt Reactor-Liquid Fuel(TMSR-LF1)are analyzed by using the creep theoretical models of UNS N1000 alloy and the numerical simulation technique of creep buckling.The results show that the TMSR-LF1 pressure vessel meets the requirements of inelastic creep-fatigue damage limit and creep buckling-instability limit under normal operating conditions.The main innovations of this paper are as follows:(1)The creep properties of Nickel-based UNS N10003 alloy at elevated temperature are studied,and a modified K-R creep damage constitutive model is proposed based on the theory of continuous damage mechanics,which can accurately simulate the inelastic creep damage behavior of UNS N10003 alloy at 650?;(2)The Lemaitre multiaxial creep-fatigue damage model of UNS N10003 at 650? alloy is obtained,which has universal applicability for the inelastic creep-fatigue damage analysis of the high temperature equipment in TMSR;(3)A creep-buckling numerical calculation method based on the modified K-R creep damage model is proposed,which considers the effect of damage on creep-buckling life and has universal applicability for the creep-buckling analysis of the high temperature equipment in TMSR.The high temperature creep theory models of UNS N10003 alloy and the numerical simulation techniques presented in this paper provide the theoretical and numerical basis of inelastic analysis for the creep-fatigue damage and creep buckling-instability assessment of the RPV in TMSR.Besides,it is a beneficial supplement to the inelastic high temperature structural integrity assessment method in ASME-NH code.The research results of this paper not only have important engineering significance for the safety assessment of the RPV in TMSR,but also have guiding significance for the creep failure research of other high temperature components.