Distribution of transmutant nickel formed in fast neutron irradiated copper

Copper and some of its alloys have been proposed to serve as high heat flux components in future fusion energy devices [l]. Unfortunately both the thermal and electrical conductivities of copper-base alloys will decline during neutron irradiation as a result of void swelling and solid transmutants [2]. The two most important transmutants are nickel and zinc, with nickel having the largest influence on conductivity degradation on a per atom basis. Recent calculation of the transmutations formed in pure copper during irradiation in the Fast Flux Test Facility (FFJ’F) predicted that N 0.41 at% nickel and N 0.40 at% zinc would be produced in pure copper after full power operation for 300 effective full power days [3]. These calculations also showed that the generation rate of nickel in typical fusion spectra would be roughly twice as large and therefore the conductivity loss would be even greater for a given level of atomic displacement. The formation and distribution of transmutants in irradiated copper alloys is currently being studied. Using copper-nickel alloys, it has been shown that during electron irradiation, nickel exerts significant influence on the evolution of dislocation microstructure and on void swelling [4-61. Radiation-induced segregation of nickel at defect sinks such as voids and grain boundaries was also reported [5,6]. Zinc was shown not to segregate, but to migrate away from such sinks, however [6]. From these studies it is clear that the properties of copper will change during neutron irradiation as nickel and zinc accumulate and then interact with point defect fluxes near microstructural sinks. The objective of the present study is to verify experimentally the transmutation calculations and to investigate whether transmutant nickel also behaves in the same manner as observed in electron irradiations.