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Simulation of Neutron Damage Microstructure in Extra
High Purity Fe-25Cr-35Ni Austenitic Stainless Steels
I. Ioka a) , Y. Ishijima b) , H. Ogawa b) and Y. Nakahara b)
a) Nuclear Engineering Research Collaboration Center, JAEA,
b) Division of Fuels and Materials Engineering, NSED, JAEA
The ultra high burn-up of LWR is considered to be an
important technology for establishing nuclear power plants
as one of the most promising future energy systems from a
view-point of reducing radioactive waste and greenhouse
gas. Cladding materials with the long excellent
performance under heavy irradiation are required to these
developments. The high chromium and high nickel
austenitic stainless steel (Extra high purity (EHP) alloy) 1)
was selected as one of candidates that are possible to be
made by the new engineering technology.
Microstructural evolution induced by irradiation is
believed to be the key variables responsible for degradation
of materials in LWR. Months to years of irradiation time
are required to obtain a change in microstructure of
materials at dozens of dpa. Charged particle simulation
with accelerated damage rate is often used in such situations
as to forecast the behavior of neutron-irradiated materials.
By establishing the correlation between charged particle-
and neutron- irradiated microstructures of EHP alloy, the
results from charged particle-irradiation can be used to
provide valuable information on microstructure evolution in
EHP alloy in LWR cores.
This work is focused on investigating the microstructure
of EHP alloy irradiated with charged particle under
condition relevant to LWR cores. The behavior of
dislocation loop is determined as a function of irradiation
temperature, and is compared to those for neutron
irradiations of EHP alloy.
The materials were Fe-25Cr-35Ni and Fe-25Cr-20Ni
EHP alloys. The chemical compositions are shown in
Table 1. The configuration of specimen is 3 mm in
diameter and 0.2 mm in thickness. The surface of
specimen was mechanically and electro-chemically polished
to a specular finish before irradiation.
The specimens were irradiated in triple (12 MeV Ni 3+ ,
1.1 MeV He + , 380 keV H + ) ion beam mode at temperatures
of 573, 673, 773 K using the triple ion beam facility
(TIARA). The temperature of the specimen was measured
by an infrared thermometer. The displacement damage in
the specimen was mainly attributed to Ni 3+ ion irradiation.
The dose was about 15 dpa around 1.2 µm. He + and H +
ions were implanted in depth ranges from 1.0 to 1.5 µm
using aluminum foil energy degraders. The concentrations
of He + and H + ions in the implanted range were 45 appmHe
and 450 appmH, which correspond to LWR condition.
Figure 1 shows the bright field image of Fe-25Cr-20Ni at
each irradiation temperature. The images show irradiation
defects such as dislocation loops are induced by charged
JAEA-Review 2010-065
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particle-irradiation. Figure 2 shows the number density
and the average diameter of dislocation loops of irradiated
Fe-25Cr-20Ni and Fe-25Cr-35Ni. The dislocation loop
density of Fe-25Cr-35Ni was less than that of Fe-25Cr-20Ni.
There is little difference in average diameter. It is
considered that Ni is effective to suppress the initiation of
irradiation defects. The dislocation loop density and the
average diameter of Fe-25Cr-35Ni by neutron irradiation
(572 K) were about 2.2 × 10 21 n/m 3 2)
and 21 nm, respectively .
The dislocation loop density and the average diameter were
almost the same for both neutron irradiation and ion
irradiation. It seems that more neutron irradiation data as a
function of irradiation temperature are necessary.
References
1) K. Kiuchi et al., IAEA-TECDOC-1299 (1999)112.
2) I. Ioka et al., JAEA Takasaki Ann. Rep. 2008 (2009) 35.
Table 1 Chemical composition of EHP alloys.
573 K 673 K 773 K
Fig. 1 Bright field image at each irradiation temperature.
Fig. 2 Dumber density and average diameter of
dislocation.