Study On H/He Synergistic Effects In SIMP Steel

The material problem is one of the key factors restricting the development of future advanced nuclear energy systems.The structural material for future advanced nuclear energy systems will be exposed to intense neutron irradiation in most case,putting for-ward higher requirements on the irradiation resistance of the material.Under neutron irradiation,the material will not only suffer from displacement damages but also be doped with larger amounts of H and He by?n,p?and?n,?transmutation.Previous studies have shown that the H/He synergistic effect can accelerate the degeneration of the material performance,seriously threatening the safety of nuclear power devices.Therefore,the study on the H/He synergistic effect is of great importance for further understanding the behavior of the material under neutron irradiation and evaluating the safety of materials used in nuclear power devices.Low activation Ferrite/Martensite?RAFM?steel has a wide application prospect in future advanced nuclear energy systems.SIMP steel is a new type of RAFM steels developed cooperatively by the Institute of Modern Physics?IMP?and the Institute of Metal Research,Chinese Academy of Sciences?CAS?,for future Lead-cooled Fast Re-actors?LFR?and Accelerator-Driven Systems?ADS?.In this thesis,taking SIMP steel as the research object,the H/He synergistic effects were investigated by using the co-irradiation of H and He ions?including the sequential irradiation and the mixed beam irradiation?to simulate H/He synergistic environment and compare with separate irra-diation of them,combing a variety of characterization techniques.1.The sequential irradiation?H+He and He+H?and mixed beam irradiation?H₂/He?of H and He ions were conducted on SIMP steel at room temperature,respectively.Af-ter irradiation,the H/He synergistic effect on vacancy-type defects was studied by Slow Positron Doppler Broadening Spectroscopy?DBS?.The results show that S parameters are significantly reduced by the presence of He as compared with H,which due to the fact that He is more easily captured by the vacancy and prefers to occupy the center of the vacancy to form a stable He-V complex.The occupation of the vacancy-type de-fect by He reduces its open volume.In the case of co-irradiation of H and He ions,S parameters are always smaller than those of H and close to those of He ions irradiation alone when the irradiation dose of H ions is lower.This reflects that the vacancy is pref-erentially occupied by He,while the He-V complex can capture H to form an He-V-H complex.2.The sequential irradiation of He and H ions?He+H?with multi-energy was con-ducted on SIMP steel at room temperature,to produce a plateau of damage and H/He concentration within the depth range of 300-600 nm from the surface.After irradia-tion,the H/He synergistic effect on the hardening behavior of the material was studied by Spherical Indenter Nanoindentation.The results show that the yield stress of the indentation is greater and the strain-softening is more significant under the sequential irradiation than under the separate irradiation of H and He ions,indicating that H/He synergistic effect promotes the hardening of the material.Based on the analysis of irradiation-induced vacancy-type defects and bubbles in the material,this effect can be attributed to the fact that the presence of He promotes the retention of H which can cooperate with He to stabilize vacancy and prevent the recombination of vacancy and interstitial,so as to promote the nucleation of bubbles and dislocation loops during ir-radiation.The inhibition of dislocation slip by bubbles and dislocations results in the enhanced hardening effect.3.The effect of H on the thermal desorption behavior of He was studied by com-parative analysis of the thermal desorption spectrum?TDS?of SIMP steel after He ions irradiation alone and additional H ions irradiation?H+He and He+H?at room temper-ature.The results show that the main peaks of He release appeared at 1198-1222 K,corresponding to the release of He by the mechanism of bubble migration.Compared with He ions irradiation alone,the peak temperature of He release is moved to low tem-peratures and the total amount of He release is increased in the case of the additional H ions irradiation.Through observations of the internal bubbles and surface morphology of the material before and after TDS,it was found that the presence of H promotes the growth of bubbles near the surface and the formation of surface blister,thereby accel-erating the process of He release via the mechanism of bubble migration during TDS heating.