Russian Federation [Example of ODS development programmes]

In 1987, the decision was taken to use in BN-350 and BN-600 reactors steels ChS68 cw and EP450 as standard materials for fuel cladding and FA wrappers, respectively. The application of EP-450 steel as 96 x 2 mm wrappers combined with CW ChS68 as 6.9 x 0.4 mm fuel claddings has reliably ensured the failure free operation of BN-600 fuel assemblies to a burnup of 11.2 at.% at a damage dose of ∼82 dpa. After the HT (HT is the normalization at 1050oC and tempering at 720 deg. C, 1 h) the microstructure of EP450 wrappers consists of ferrite and tempered martensite grains with approximately 1:1 ratio. The microstructure is characterized by presence of rounded MC and M23C6 precipitates in the grain interior and along grain boundaries, with particle diameters ranging from 0.05-0.2 μm. The lath boundaries in grains of the tempered martensite contain some smaller (up to 0.1 μm) blocky precipitates of M23C6. Dislocations in the ferrite are uniformly distributed and their density is 2 x 1014 m-2. The dislocation density in the tempered martensite is 1 x 1015 m-2 and they are non-uniformly distributed intragranularly, forming low angle boundaries. Since the swelling behaviour of ChS68 steels limits the fuel burnup, it is desired that the cladding also be EP-450 but modified as an ODS option so that it retains sufficient strength at high temperatures. The method chosen is mechanically alloying. - Production of steel powder having the matrix composition (EP450) by the centrifugal atomization of the molten mass from a revolving crucible in high purity helium; - Mechanical alloying of the resultant powder with nano-particles (40-80 nm) of Y2O3 in vibrating high-energy attritor; - Vibro-filling the steel cans with the received powder blend, followed by degassing and sealing of cans; - Hot extrusion at ∼1150 deg. C of cans containing a powder blend to produce a hot-extruded bar at the drawing of no less than 10 and its subsequent working; - The quality of the final product is influenced by the production method of the yittria particles. In the initial production yittria of industrial production was used. The properties of the second production were improved by the use of yittria particles produced by special technology. Examples of particles are shown; - The different microstructures produced in bars are shown; - The microstructure of a finished tube are shown. The structure of the produced tubes consists of equiaxed subgrain sizes ranging from 0.1-3 μm. Uniformly distributed oxides are observable within grains and subgrains. The size distributions of the oxides are illustrated. The mean size of the oxide particles is about 7 mm, their concentration is ∼1016 cm-3. The ODS samples are under irradiation in BN-600 reactor within two materials FAs up to the damage dose of ∼140 dpa beginning on 2010. (author)