The main results of development work and post-reactor studies of different structural materials for fuelelement cladding and hexahedral fuel-assembly jackets for sodium-cooled fast reactors are examined. Austenitic and ferritic-martensitic steels, including steel obtained by powder metallurgy, are examined as promising materials for fuel-element cladding for staged increase of fuel burnup.Successful work on and development of fast reactors are largely determined by the functional properties of the structural materials at high damaging dose. The most important characteristics are the swelling and creep, which determine the shape change of articles, and the degradation of the mechanical properties.The Bochnar All-Russia Research Institute for Inorganic Materials (VNIINM) is developing fuel elements and structural materials in close cooperation with Afrikantov Experimental Design Bureau of Mechanical Engineering (OKBM), which is the main contractor, and the Leipunskii Institute for Physics and Power Engineering (FEI), which is the scientific direactor for fast reactors. The results of post-reactor studies, which are being conducted at the Beloyarskaya nuclear power plant, at IRM, the Research Institute for Atomic Reactors (NIIAR), and the FEI, are very important for making decisions. The objects of post-reactor studies are materials-engineering, experimental, reference, and standard fuel assemblies.The objective of the first comprehensive program for the development of radiation-resistance materials was to develop steel that would give burnup of at least 10% h.a [1]. In this program, the following steels were tested: austenitic steel in various states of mechanical-heat treatment -08Kh16N11M3, 08Kh16N11M3T, 06Kh16N15M3B (EI-847), 06Kh16N15M3BR (EP-172), 06Kh16N15M2G2TFR (ChS-68); ferritic-martensitic steel Kh13M2BFR (EP-450), 05Kh12N2M, Kh12MSFBR (EP-823); and high-nickel alloys with 30-40% nickel. In 1987, it was decided on the basis of the results of the tests to use in BN-600 ChS-68 c.d. and EP-450 steels, respectively, as the standard materials for the fuel-element cladding and fuel-assem-
