Study On Mechanical Properties Test Method Of Reactor Structural Materials Irradiated By High-energy Ion

With the progression of society,the environmental issues resulting from traditional fossil fuels have become increasingly severe.As a result,nuclear energy has emerged as a significant alternative.Among the various types of reactors,the pressurized water reactor(PWR)is the most commonly used due to its high conversion efficiency,effective moderating ability,compact structure,and high core power density.However,the harsh conditions within the reactor,including high temperature,high pressure,and strong neutron irradiation,lead to material degradation over time.Despite the high construction costs of nuclear power plants,the economy of operating a PWR can be significantly improved by extending the life of these power plants and improving their life evaluation.The ion irradiation damage rate produces a high level of displacement,and cascading damage similar to that caused by neutron irradiation.Such as,ion irradiation is often employed in place of neutron irradiation in order to reduce the cost of irradiation experiments and the radioactivity of the irradiated sample.As the depth of the ion irradiation layer is relatively shallow,ion irradiation samples typically consist of a "composite sample" comprising both an irradiated layer and an unirradiated layer.Consequently,it is not possible to calculate the mechanical properties of the irradiated layer using empirical correlation formulas.With these considerations in mind,in this study,high-energy ions generated by an accelerator were utilized to replace neutrons in the irradiation process,accelerating the damage of materials and enabling systematic analysis of their mechanical properties.Furthermore,the inverse finite element(FE)method was used to obtain the stress-strain relationship of irradiated materials,which may lead to a more scientific method of evaluating the lifetime of active reactors.The main research contents are exhibited as follows:(1)Through the small punch test(SPT),it was discovered that the loaddisplacement curve(LDC)was greatly influenced by the thickness of the samples and the ball movement rate.Additionally,FE simulation revealed that the ball diameter,friction coefficient,and hole diameter of the clamping device also had an important impact on the LDC.The 316 L stainless steel SPT test was conducted systematically,and the results indicated that the ratio of yield load to the square of the thickness was a constant value.And the maximum load of the SPT was positively correlated with the speed of punch movement.Furthermore,a two-dimensional axisymmetric model of the SPT was established using FE software.The FE simulation results demonstrated that the maximum load was improved with increasing friction coefficient and ball diameter.And the maximum load decreased with an increase in the aperture of the lower fixture.(2)The mechanical properties of the irradiated layer of A508-3 steel were determined using the inverse FE method.Results from nanoindentation testing indicated that the inverse FE method was accurate for irradiated materials.To obtain the material property of the sample irradiation layer in the FE model,a uniaxial tensile test of unirradiated A508-3 steel was conducted systematically and stress-strain curves were assumed for 861 different materials.Following this,batch FE simulation was used to obtain the corresponding 861 simulated LDCs and stress-strain curves.A mapping database of LDCs and stress-strain curves for FE was established.And LDCs for 0.05 dpa and 0.30 dpa samples were obtained by SPT.The simulation LDCs were then matched to the experimental LDCs of the irradiated sample found in the database,and the resulting stress-strain curve was used to determine the mechanical properties of the irradiated layer.