The 5 mm-wide ring-tensile specimens with a 1.5 mm-wide gauge section were prepared from the cladding of 12Cr-ODS steels (F94, F95, and 1DS) and 9Cr-ODS steels (M93).67 This type of specimen makes it possible to test mechanical properties in the hoop direction of the cladding. These ring-tensile samples were irradiated in the experimental fast reac­tor JOYO using the material irradiation rig at tem­peratures between 400 and 534 °C to fast neutron fluences ranging from 5.0 x 1025 to 3.0 x 1026nm~2 (E > 0.1 MeV). The yield strength of the irradiated samples as a function of test temperature is shown in Figure 39, together with that of the unirradiated ones.67 After irradiation, the yield strength of irra­diated F94, F95, and M93 cladding, is modestly higher (<10%) than that of the unirradiated ones at all test temperatures, due to irradiation hardening. Figure 40 plots uniform elongation before and after irradiation as a function of test temperature.67 Uniform elongation for unirradiated F94 and F95 cladding is almost the same at all test temperatures, and that of M93 is lower in relation to strength. Uniform elongation in the hoop direction for all three claddings is more than 3% at these test temperatures, though that of 1DS was particularly low (<1%) due to its microstructural anisotropy, as shown in Figure 17. Figure 40 indicates that there is no significant degradation in uniform elongations for F94, F95, and M93, due to irradiation. This indicates that the microstructural improvement by recrystallization or a-g-phase transformation is quite effective in maintaining well-balanced mechani­cal properties for ODS steel cladding, especially those of strength and ductility, not only for as-received con­ditions but also following irradiation.

In-pile creep rupture tests were conducted in JOYO using the Material Testing Rig with Tempera­ture Control (MARICO-2) as a new irradiation test device.68 The test specimens were prepared from the claddings of 9Cr-ODS steel (Mm14) and 12Cr-ODS steel (F14). Both end-plugs of the specimens were joined by means of pressurized resistance welding (PRW). The hoop stress was set by adjusting the pres­sure of the enclosed helium gas. To identify the rup­ture of time and specimens, a unique blend of stable

Table 3 Historical survey of yttrium-titanium-oxides reported to be stable under radiation Author Material Irradiation particle (dpa) Temperature (°C) Dose (dpa) Dose rate (dpa s 1) Result Pareige et al.74 12YWT 150 keV Fe 300 0.7 1.9 x 10~4 Stable dispersions Asano et al.75 MA957 1 MeV He (+) 450 150 2 x 10~3 Stable oxides 4 MeV Ni 650 Hide etal.76 MA957 42 keV He 475 200 1.0-1.4 x 10~2 Stable oxides at 25°C(+) 525 200 keV C~ 575 625 Hide etal.76 MA957 220 keV He at 25 °C 475 150 3.0 x 10~3 Stable oxides (+)3 MeV Ni+ 525 Little77 DT2203YO5 52 MeV Cr6 + (+) 475 50 3.0 x 10~4 Stable oxides 4 MeV He Saito et al.61 13Cr-0.5TiO2 -0.2Y2O3 1 MeV electron 400 12 2.2 x 10~3 Stable oxides 500 Kinoshita et al.78 13Cr-ODS (+) Nb, V, Zr 1 MeV electron 350 15 2 x 10~3 Stable oxides 450 Akasaka et al.79 9Cr and 12Cr-ODS JOYO 330 7.0 Not reporteda Stable oxides 400 2.5 450 14.0 500 15.0 Mathon etal.80 MA957 Thermal neutrons 325 0.8, 2.0 1 x 1014 ncm~2 Stable dispersions (OSIRIS) 3.5, 5.5 (E > 1 MeV) Monnet etal.63 DY EM10+Y2O3EM10 + MgO 1 MeV Helium 400 0.05 Not reported No change in oxide particles

Kimura et al.81 (13-19)Cr-4Al-ODS 300 20 1 x 10~4 No reported change in oxide size -500 aTypical fast reactor displacement rates in the driver fuel portion of the core are 1 x 10 6dpas 1. Source: Reproduced from Allen, T. R.; Gan, J.; Cole, J. I.; et al. J. Nucl. Mater. 2008, 375, 26-37.

aTypical fast reactor displacement rates in the driver fuel portion of the core are about 1 x 10 6dpas 1 Source: Reproduced from Allen, T. R.; Gan, J.; Cole, J. I.; et al. J. Nucl. Mater. 2008, 375, 26-37.
• F94 — F94 unirrad. □ F95 — F95 unirrad. A M93 M93 unirrad. О 1DS — 1DS unirrad.
8
sP O’
6
4
2
(3.56)
(0.45)

xenon and krypton tag gases was enclosed. The irradi­ation temperatures were 700, 725, and 750 °C, and the hoop stress ranged from 45 to 155 MPa. The maximum neutron dose reached 20 dpa. It was confirmed that in­pile creep rupture time is located within the out-of­pile data band, and there is no degradation in creep strength due to irradiation.68

MA957 and MA956 were irradiated in Fast Flux Test Facility (FFTF)-Materials Open Test Assembly (MOTA) at 420 °C up to 200 dpa.69 No voids were seen in this area, but precipitates did appear, which were expected to be a0. The results regarding the radiation damage resistance of ODS steels were highly encourag­ing. Evidence was apparent in both MA956 and MA957

of a0 precipitation, and in regions where recrystalliza­tion occurred before irradiation in MA957, a few voids were slightly observed. Gelles69 pointed out that these could be overcome by employing suitable alloy design and that ODS steel microstructures, when properly manufactured to provide a uniform oxide dispersoid in a structure, appear to be completely resistant to radiation damage at doses as high as 200 dpa.