TRANSMUTATION-INDUCED EMBRITTLEMENT OF VANADIUM AND SEVERAL VANADIUM ALLOYS IN HFIR

Vanadium, V-1Ni, V-10Ti and V-10Ti-1Ni (at%) were irradiated in HFIR t o doses ranging from 18 to 30 dpa and temperatures between 300 and 600 degrees C. Since the irradiation was conducted in a highly thermalize d neutron spectrum without shielding against thermal neutrons, signifi cant levels of chromium (15-22%) were formed by transmutation. The add ition of such large chromium levels caused strong embrittlement, At hi gher irradiation temperatures radiation-induced segregation of transmu tant Cr and solute Ti at specimen surfaces caused strong increases in the density of the alloy, The resultant shrinkage, possibly compounded by thermal cycling, led to cracks developing at all intersections of grain boundaries with the specimen surface, This caused specimens irra diated at 500 degrees C or below to often fail during retrieval from t he reactor, as well as during electropolishing and other handling oper ations. At 600 degrees C, the cracking and embrittlement processes are so severe that only a fine dust, composed mostly of individual grains or chunks of grains, was found in the irradiation capsule.