(A) study on the recovery of radiation hardening of PWR pressure vessel steel using microhardness and positron annihilation

Abstract

A post-irradiation annealing study was conducted with use of reactor pressure vessel (RPV) steel A533B Cl.1 base metal irradiated at about 280℃ with a dose of $4.84\times10^{18}n/㎠$. Microhardness and positron annihilation (PA) methods were used to obtain better understanding of recovery of radiation hardening. Isochronal anneal experiments indicate that two recovery processes occur during annealing of irradiated specimens. The first recovery process occurs in the temperature range of 280-305℃. The variations of Ip, Iw and R parameters indicate that formation of vacancy clusters by vacancy agglomeration and annihilation of monovacancies from defect surfaces are associated with the first recovery process. The second recovery process occurs in 405-490℃ and positron annihilation parameters measured indicate that dissolution of carbon atoms decorated around vacancy-type defects and other possible precipitates, and annihilation of monovacancies are attributed to the second recovery process. It is further indicated that radiation anneal hardening (RAH) in the mid-temperature range of 305-405℃ between the temperature ranges for the two process occurs due to formation of carbon-decorated vacancy clusters and precipitates. The activation energy, order of reaction and other characteristics of recovery processes were determined by the Meechan-Brinkman method. The activation energy for the first recovery process was determined as 1.76 eV and that for the second recovery process as 2.00 eV. These values are lower than those obtained by other workers. This difference may be attributed to the lower copper content of the RPV steel used in the present study. The order of reaction for the first recovery process was determined as 1.78, while that for the second recovery process as 1.67. Non-integer orders of reaction for recovery processes seem to be attributed to the fact that several mechanisms for the first order and the second order of reaction are compounded in one ...