[en] The progress of the Reduced Enrichment Research and Test Reactor (RERTR) Program is described. After a brief summary of the results which the RERTR Program, in collaboration with its many international partners, and achieved by the end of 1985, the activities, results, and new developments which occurred in 1986 are reviewed. The second miniplate series, concentrating on U₃Si₂-Al and U₃Si-Al fuels, was expanded and its irradiation continued. Postirradiation examinations of several of these miniplates and of six previously irradiated U₃Si₂-Al full-size elements were completed with excellent results. The whole-core ORR demonstration with U₃Si₂-Al fuel at 4.8 g U/cm³ is well under way and due for completion before the end of 1987. The US DOE removed an important barrier to conversions by announcing that the new low-enrichment uranium (LEU) fuels will be accepted for reprocessing. New DOE prices for enrichment and reprocessing services were calculated to have minimal effect on high-enrichment uranium (HEU) reactors, and to reduce by about 8-10% the total fuel cycle costs of LEU reactors. New program activities include preliminary feasibility studies of LEU use in DOE reactors, evaluation of the feasibility to use LEU targets for the production of fission-product ⁹⁹Mo, and responsibility for coordinating safety evaluations related to LEU conversions of US university reactors, as required by NRC. Achievement of the final program goals is projected for 1990. This progress could not have been achieved without close international cooperation, whose continuation and intensification are essential to the achievement of the ultimate goals of the RERTR Program