AbstractBased on an examination of thermal and fast reactor fission yield data, specific fission products are recommended as burnup monitors for total fissions in various reactor fuel types and for fractional fissions in235U-239Pu and233U-235U reactor fuels. Emphasis is placed on long-lived and stable fission products determined by mass spectrometry. The types of monitors include a single fission product for total fissions and the ratio of two fission product isotopes of the same element both for total fissions and fractional fissions.