Ion Irradiation Damage Of Tungsten,Reduced Activation Steel And Austenitic Steel

Irradiation damage of nuclear materials is the key point of future advanced nuclear systems development.Tungsten is considered as the most important candidate as the plasma facing material of fusion reactor.It suffers from the irradiation of hydrogen isotopes and helium.Reduced-activation ferritic/martensitic steel is one of the structure material candidates of fusion reactor.Besides neutron damage,helium and hydrogen atoms are also introduced into fusion reactor structure materials due to nuclear transmutation reaction.Modified 310S stainless steel has been chosen as the structure material of CSR1000,a supercritical water reactor designed by China.However,irradiation swelling may be a problem for this material.Synergistic effect of helium and hydrogen on helium bubble in tungsten,helium behavior in reduced-activation ferritic/martensitic steel and microstructure evolution of 310S steel modified with different elements under irradiation were investigated in present study.1.Irradiations of He~+and H~+have been performed to investigate the effect of H~+ irradiation on existing helium bubbles and the effect of pre-irradiation of H~+on the formation of helium bubbles in tungsten.The specimens were irradiated at 800? with either 10keV-H~+,20keV-He~+,or sequentially irradiated with both H~+ and He~+.After H~+irradiation,existing helium bubbles were observed to growth.Helium bubbles are effective trapping sites for hydrogen atoms.Trapped hydrogen atoms could enter helium bubbles as hydrogen molecules,leading to bubble growth.Enhancement on the nucleation of helium bubbles due to pre-or post-irradiation of H~+was also observed.More vacancies were introduced by H~+ irradiation.Vacancies prefer to capture helium atoms rather than hydrogen atoms and lead to helium bubble nucleation.Hydrogen bubbles grew to larger sizes after post irradiation of He~+.2.The mechanism of helium behavior in reduced-activation ferritic/martensitic steels was investigated systematically.At different temperatures,specimens were irradiated with He~+with different energies to various fluences.After irradiation, specimens were characterized with positron annihilation Doppler broadening measurement and thermal desorption spectroscopy.A threshold fluence was observed.Above the fluence,the rate of helium bubbles formation and growth increased dramatically.As fluence is relatively low,concentration of He_nV_m clusters is small,limiting formation of helium bubbles.At higher temperature,the formation and growth of He_nV_m clusters with low binding energies were suppressed and those of helium bubbles and He_nV_m clusters with high binding energies were enhanced.After the irradiation temperature rose from 250? to 450?,different responses of S parameters were observed in various depths. Irradiation of 18 keV-He~+enhanced He_nV_m clusters and helium bubbles growth compared with 100 keV-He~+irradiation.18keV-He~+increases concentrations of helium atoms and vacancies.The ratio of helium atoms and vacancies is also larger,resulting in more effective loop punching mechanism.3.The effect of oversized additive atoms on microstructure evolution in 310S stainless steel under irradiation was investigated.Irradiations of 120-keV Ar~+ were conducted on two types of modified 310S stainless steel at 290? and 550?.SC-1 was modified with Zr and SC-2 was modified with Nb,Ta,and W. Compared with SC-2,low density,smaller cavities formed in SC-1 at 290?.In SC-1,the recombination rate of point defects is larger as the nucleation rate of cavity is smaller.When the temperature was increased to 550?,different cavity behaviors and precipitates were observed in the two materials.Precipitates enriched with Ni were observed in SC-1,while Nb-and Ta-enriched precipitates were found in SC-2.Cavities in SC-1 became larger.The density of them became smaller.Zr atoms acted mainly as nucleation sites rather than recombination sites.High binding energy between Zr atoms and vacancies also promoted cavity growth.The density and size of cavities in SC-1 both increased when temperature increased.Precipitate of Nb and Ta decreased the concentration of solute atoms, resulting in a smaller defect recombination rate.