This is the final report in an experimental and theoretical program to develop and apply single- and few-element methods for the determination of reactor lattice parameters. The period covered by the report is January 1, 1968 through September 30, 1970. In addition to summarizing results for the entire contract period, this report also serves as the final annual report; thus, work completed in the period of October 1, 1969 through September 30, 1970 is dealt with in more detail than the earlier work. Methods were developed to measure the heterogeneous parameters 17, [Gamma] [eta] and [Alpha] for single fuel elements immersed in moderator in an exponential tank using foil activation measurements external to the fuel. These methods were applied to clustered fuel rods in D 20 moderator and single fuel rods in H 20 moderator, and the results were extended to and compared with data on complete multi-element lattices reported by other laboratories. Advanced gamma spectrometric methods using Ge(Li) detectors were applied to the analysis of both prompt and fission product decay gammas for the nondestructive analysis of the fuel used in this work. The latter includes both simulated burned fuel containing plutonium and actual burned fuel irradiated to 20,000 MWD/T in the Dresden BWR.