Bi2Sr2Ca2Cu3Ox(Bi-2223) tapes were processed by the standard powder-in-tube technique, but small amounts ofUO4were added prior to processing. Both U-doped and undoped tapes were subsequently exposed to a reactor spectrum of neutrons. Whereas the undoped materials show moderate enhancements of the critical current densitiesJcdue to the pinning action of the fast-neutron-induced collision cascades,Jcin the U-doped tapes increases by factors of 10–20 due to thermal-neutron-induced fission of235Uand the subsequent formation of fission tracks. Since the enhancements are particularly pronounced, when the magnetic field is applied perpendicular to the tape surface, the characteristicJcanisotropy is strongly reduced in a certain field range. At the same time, the irreversibility field at 77 K is doubled for both field orientations. ©1998 American Institute of Physics.