Fabrication and characterization of 15Cr-15Ni austenitic steel cladding tubes for sodium fast reactors

Abstract : Two fabrication routes requiring industrial facilities are being conducted to produce several hundred 15Cr-15Ni cladding tubes. The processing methods involve varying degrees of cold work and different heat treatment conditions. In order to ensure that the specifications are fulfilled, both batches of tubes are fully characterized regarding several aspects. The microstructure is observed using optical and electron microscopy. A refinement of the grain size is detected in the inner diameter of one batch, which is caused by a nitrogen contamination revealed by glow discharge mass spectrometry analysis. The precipitates are also carefully analyzed. Selective dissolutions are performed on both batches to determine their mass fractions. The precipitates (TiC, TiN and Ti$_2$CS) are identified using X-ray diffraction. The titanium content in solid solution is measured and the resulting values are analyzed to assess the quality of the last solution annealing. The tensile properties measured at room temperature comply with those expected for this steel grade. On the basis of our results and considering past experience with cladding irradiated in Phenix reactor a good behavior in pile can be foreseen for these tubes.