NbTi and Nb 3 Sn multifilamentary composites have been irradiated with fast-neutrons at 60 ± 5°C to fluences of 1.2×10 ²⁰ n/cm ² (E > 1 MeV). The NbTi samples show only a moderate reduction of I c as a function of neutron fluence in an applied field of 40 kG. Reductions in I c were observed for fluences greater than 3 × 10 ¹⁷ n/cm ² and saturate at 18% for fluences greater than 3-4 × 10 ¹⁹ n/cm ² . The Nb 3 Sn composites showed large neutron radiation induced changes in T c , I c and H c2 . Reductions in T c were observed for fluences greater than 7 × 10 ¹⁷ n/cm ² . No measurable changes in I c (40 kG) were observed below 10 ¹⁸ n/cm ² . Between 2 and 3×10 ¹⁸ n/cm ² , however, there is an apparent threshold where a very rapid reduction in I c (40 kG) is initiated. At the threshold the decrease in T c is 13%. Between the threshold and 1.1 × 10 ¹⁹ n/cm ² , I 2 (40 kG) has been reduced to 4% of the unirradiated value. These changes in superconducting properties in NbTi and Nb 3 Sn are analyzed in terms of the radiation induced defects. The impact of the response to irradiation of both materials on their applications in fusion reactor magnets is discussed.

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