Mechanical And Numerical Simulation Analysis Of Irradiation Charpy Specimen Reconstitution

The pressure vessel is the most critical equipment in the reactor,and its structural integrity is directly related to the operational safety and service life of the reactor.In practical applications,the aging degree of the pressure vessel can be evaluated by the ductile-brittle transition temperature curve of the Charpy impact specimen pre-placed in the irradiation supervision tube of the pressure vessel.Actually,due to the compactness of the reactor internals,there are limited irradiation surveillance specimens available for mechanical testing.To address the shortage of irradiation surveillance specimens due to limited space in nuclear reactors,specimen reconstitution techniques are used to gather more impact data to support the life extension of the nuclear power plant.However,the existing specifications for specimen reconstitution,which only give the corresponding minimum standards,do not achieve a reasonable maximum utilisation of the impact fracture.In addition,reasonable and effective finite element models to verify the reconstituted specimens are lacking.In this paper,the reactor pressure vessel Ni-Cr-Mo-V steel is used as the research object,and the Charpy impact specimens are prepared by selecting the base material,welds and heat affected zone.The maximum plastic deformation of the impact fracture was determined through microhardness analysis and the impact process was verified using the GTN model.Subsequently,the electron beam welding was used to process the reconstituted specimen of the base material,and the effectiveness of the reconstituted specimen was further verified through impact testing and finite element analysis of the impact process in combination with the reconstituted specimen.The main findings are as follows:(1)The ductile brittle transition temperatures for the base material and welds of the RPV steel were determined to be-73.5℃ and-36℃ respectively,indicating that the base material has better toughness.(2)Hardness tests were carried out on the impact fractures of the base material,welds and the heat affected zone on the upper shelf to determine the maximum plastic deformation size of the RPV steel.The data shows that the maximum length of plastic zone of the base material,welds and heat affected zone impact fracture were 7.0 mm,6.5 mm and 8.5 mm,respectively.The insertion length of the reconstituted specimen for the RPV steel should not exceed 19mm.(3)The GTN model was used to simulate the impact process on the upper shelf of the base material and welds,and the load-displacement curve obtained was basically consistent with the test results.The deviation of the impact energy was less than 5%.The contour of the plastic zone in the simulated plastic graph match the test result,verifying the validity of the GTN model.(4)The load-displacement curves of the theoretical simulation of the reconstituted specimens of the base material were similar to the original specimens,and the deviation of the impact energy was less than 5%.The impact energy of the reconstituted specimen was within the baseline verification data of the original specimen,and the plastic zone length of the fracture was approximately 7.5mm,which was almost the same as the original material.The above conclusions show that the reconstituted specimen used the sampling method was feasible,the welding method was reasonable,and the impact data of the reconstituted specimen was valid.