Vanadium alloys, including the highly purified V-4Cr-4Ti alloy called NIFS-Heat2, in the form of sodium-enclosed irradiation capsules, were irradiated up to a damage level of 5 dpa in the Joyo reactor at temperatures from 395 to 601 degrees C. An increase of the ductile - brittle transition temperature (DBTT) by neutron irradiation and irradiation hardening were observed. No significant loss of ductility was observed even for irradiation at 395 and 450 degrees C. The addition of titanium to V-Cr alloys was effective for irradiation hardening at high temperature. Hydrogen uptake in the cleaning process during dismantling of the irradiation capsules caused ductility loss of the highly purified V-4Cr-4Ti alloys; the alloys recovered their ductility when they were annealed at 400 degrees C in vacuum. The uniform formation of Ti(OCN) precipitate was suppressed in highly purified V-4Cr-4Ti alloys irradiated in Joyo in a liquid-sodium environment. (C) 2008 Elsevier B.V. All rights reserved.