Abstract
The behavior of transmutation helium during isochronal annealing of irradiated Eurofer 97 was investigated using coincidence Doppler broadening spectroscopy (CDBS). The investigated ferritic martensitic steel was irradiated in 2000 and 2001 in the frame of the STIP-II project at the Swiss neutron spallation source (SINQ) (irradiation with neutrons and protons) at the Paul Scherrer Institute (PSI).
During isochronal annealing experiment, coarsening of vacancy clusters and/or growth of helium bubbles was observed at T }= 500 degrees C. This process causes an increase of low-momentum annihilation events and related increase of the S parameter during thermal treatment of material.
On the other hand, the maximum concentration of helium in small vacancy clusters (V-n) was observed after annealing at 400 degrees C, where an excellent correlation with the calculated CDBS profiles of V-n + He-m clusters was found. (C) 2014 Elsevier B.V. All rights reserved.