Experimental irradiations of pressure vessel materials were conducted at the Saxton reactor and Babcock & Wilcox Test Reactor to provide radiation effects data for fast neutron fluences up to 1 × 1020 n/cm2 (E > 1 MeV). Included in the capsule assemblies were 237Np and 238U dosimeters and 54Fe correlation monitors. The activities of the dosimeters were combined with the neutron spectrum calculations of a multigroup diffusion code to establish the fast-neutron (E > 1 MeV) fluences experienced by the dosimeters. For both reactors the fluences derived from the different dosimeters were in good agreement indicating both the adequaey of the spectral predictions and the successful application of the fission dosimeters. It is shown that the 237Np and 238 U dosimeters are responsive to a wider range of neutron energies than the more commonly used threshold detectors and are therefore better able to ensure the aptness of calculated neutron spectra. This effort has indicated that the use of 237Np and 238U dosimeters in power reactor vessel surveillance programs leads to more meaningful correlations between neutron fluence and induced radiation effects.