The irradiation behavior of copper and copper alloys has been extensively studied up to high doses (>100dpa) for irradiation temperatures of ^400- 500 °C.60 Most of the irradiation experiments of cop­per and copper alloys have been done in mixed spectrum or fast reactors, such as HFIR, Fast Flux Test Facility (FFTF), or EBR-II. It should be noted that the accumulation rate of helium in copper in fusion reactors is significantly higher than in fission reactors (~10 appm dpa-1 in fusion reactors vs. 0.2 appm dpa-1 in fast reactors).22 Attention must be paid to transmutation effects such as helium when the irradiation data of copper and copper alloys from fission reactors are applied for fusion reactor design.

4.20.5.1 Effect of Irradiation on Physical Properties of Copper and Copper Alloys

Neutron irradiation leads to the formation of trans­mutation products and of irradiation defects, dis­location loops, stacking fault tetrahedra (SFT), and voids. All these features result in reduction of electrical and thermal conductivities.36,37,61-63 At irradiation temperatures between 80 and 200 °C, the electrical resistivity is controlled by the forma­tion of dislocation loops and stacking fault tetra- hedra and transmutation products. The resistivity increase from radiation defects increases linearly with increasing dose up to ~0.1 dpa and saturates. The maximum measured resistivity increase at room temperature is about ~6%. At irradiation tempera­tures above ^200 °C, the conductivity change from extended radiation defects becomes less significant, and void swelling becomes important to the degrada­tion of the electrical conductivity.

Fusion neutrons produce a significant amount of gaseous and solid transmutation products in copper. The major solid transmutation products include Ni, Zn, and Co. The calculated transmutation rates for copper in fusion first wall at 1 MW-year m-2 are 190appmdpa-1 Ni, 90appmdpa-1 Zn, and 7 appm dpa-1 Co.2 Ni is the main transmutation element that affects the thermal conductivity of copper. It should be noted that water-cooled fission reactors would produce significantly higher transmutation rates of copper to Ni and Zn (up to ^5000 and 2000 appm dpa-1, respectively) because of thermal neutron
reactions. The data from fission reactor irradiation experiments must be treated with care when they are applied for fusion design.