Kinev E.A.1, Pastuhov V.I.1,2, Glushkova N.V.1
1. Institute of Nuclear Materials, Zarechny, Russia
2. Eltcin Ural Federal University, Ekaterinburg, Russia
Liquid-metal corrosion produces negative influence on the Cr-Ni class steels which contact with sodium coolant of nuclear reactor. Corrosion behaviour of ChS-68 and EK-164 cold worked cladding steels under long-term (from 3600 to 17500 hours) irradiation in circulating stream of reactor pure sodium in primary coolant circuit of fast power reactor core in the temperature range between
370-620ºC with subsequent wet storage in the storage pool is investigated with metallography, scanning electron microscopy, X-ray spectroscopy and X-ray diffraction analysis methods. Liquid-metal corrosion mechanism for examined steels corresponds to physical-chemical dissolution. Selective nickel release from solid solution is observed. Steel surface depletion in nickel up to 2-5 wt.% is accompanied with γ→α transformation. NaCrO2 and Na2Cr2O7 compounds are not observed in corrosion products, whereas it is possible that there is Na2CrO4. Steel corrosion damages by the time of examination after wet storage show pitting behavior without intergranular interaction with sodium and water and independent on the grain size, junctions with spacers are not exposed to abrasion and accelerated corrosion. In general liquid-metal corrosion depth and intensity at operated coolant rates are determined by irradiation temperature and time. Value variations are related to variation of sodium stream velocity inside fuel assembly channels. Limit value for corrosion depth is 15-17 µm at corrosion rate below 9 and 7.5 µm/yr for ChS-68 and EK-164 steels, respectively.
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