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Ferritic alloys have some promise for duct and cladding applications for liquid metal fast breeder reactors (LMFBR) because of their favorable neutron absorption cross sections. Two alloys of the 10 to 12 percent chromium class, EM-12 and HT-9, have been selected for study in the National Alloy Development Program. Bombardment with 2.8 MeV 56Fe+ ions and transmission electron microscopy (TEM) observations were used to determine the temperature dependence of swelling at 150 displacements per atom (dpa) and the swelling rate at the peak swelling temperature up to 250 dpa. Both alloys were found to be more swelling resistant than Type 316 stainless steel, with EM-12 having a swelling rate of 0.011 percent/dpa at the peak swelling temperature of 550°C (1022°F) while HT-9 had a swelling rate of 0.017 percent/dpa at the peak swelling temperature of 500°C (932°F). An unusual feature of swelling in these materials was the formation of very large voids on precipitates along the grain boundaries.

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