[en] A series of high-performance in situ composite conductors have been studied to determine the detrimental effects of neutron irradiation on the upper critical field, the transition temperature and the critical current. For fluences up to 1 x 10₁₈ n/cm₂, there is essentially no degradation of any of the superconducting properties. At 7 x 10₁₈ n/cm₂, however, T_c has dropped to 13 K and at 10₁₉ neutrons n/cm₂ T_c has dropped to 9 K. The ratio of H_c2T_c is essentially constant at 1.0 T/K for fluences out to 1.3 x 10₁₉ n/cm₂. The volume pinning force goes as (1-b)₂ for all samples indicating that shear in the flux line lattice controls J_c even for samples with T_c as low as 6 K