Swelling Behavior of Commercial Ferritic Alloys, EM-12 and HT-9, as Assessed by Heavy Ion Bombardment

Abstract

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.

Microstructural stability of an HT-9 fuel assembly duct irradiated in FFTF

“…Using ion irradiation at 550°C a peak swelling of 4.7% was observed at 250 dpa, revealing an ion-induced steady-state swelling rate of 0.017%/dpa [43]. Based on these few data and the current observations alone it is not yet possible to confidently predict the swelling or swelling rate for HT-9 at high exposures and the full range of reactor-relevant temperatures.…”

The co-evolution of microstructure features in self-ion irradiated HT9 at very high damage levels

“…Ion irradiation, in addition to offering the benefits of accelerated damage rate and excellent temperature control, can provide systematic data sets that can be easily integrated into rate theory models [1,[12][13][14][15][16][17][18]. Furthermore, ion irradiation has been shown to be quite a successful method for emulating reactor damage especially for the purpose of materials selection prior to qualification of in test reactors [1,15,19].…”

Microstructural changes and void swelling of a 12Cr ODS ferritic-martensitic alloy after high-dpa self-ion irradiation

“…A value of 40 eV displacement threshold energy and the Kinchin-Pease option were used for the damage calculations [29,30]. The irradiation temperature was controlled to be 475 ± 10 ºC to maximize swelling based on previous determinations of peak swelling temperatures [25,[31][32][33]. The chamber vacuum during irradiation was better than 1×10 -6 torr.…”