Bi2Sr2Ca2Cu3Ox (Bi-2223) tapes were processed by the standard powder-in-tube technique, but small amounts of UO4 were 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 densities Jc due to the pinning action of the fast-neutron-induced collision cascades, Jc in the U-doped tapes increases by factors of 10-20 due to thermal-neutron-induced fission of 235U and the subsequent formation of fission tracks. Since the enhancements are particularly pronounced, when the magnetic field is applied perpendicular to the tape surface, the characteristic Jc anisotropy 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.