JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

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Radiation-Induced Electrical Degradation in CeO2
Ceramics Irradiated with 10 MeV Ni
N. Ishikawa and K. Takegahara
Division of Fuels and Materials Engineering, NSED, JAEA
Radiation damage is one of the important causes of
degradation of thermal conductivity and serious swelling in
nuclear ceramic fuels. Understanding of radiation damage
in nuclear fuel is important for controlling fuel properties
during burn up. One of main objectives of this study is to
elucidate the irradiation parameter dominating the radiation
damage of ceramics by means of accelerator experiments,
and to develop the characterization method of the radiation
damages. Especially for simulating the process of
radiation damage by elastic displacements, low-energy
particle (10 MeV Ni) irradiation experiment has been
performed. The oxide ceramics target, CeO 2, which has
the same crystal structure (fluorite structure) with a UO 2
nuclear fuel is adopted. In the present study, the radiation
damage behavior is characterized not only by the X-ray
diffraction method but also by the electrical conductivity
measurement method.
Thin films of CeO 2 were prepared on Al 2O 3 single
crystal substrates, and were irradiated with 10 MeV Ni ions
at room temperature. After the irradiation, fluence
dependence of change of X-ray diffraction (XRD) pattern was
measured in the wide fluence range up to 1.0 × 10 16 ions/cm 2 ,
and also the electrical conductivity was measured up to about
1 × 10 16 ions/cm 2 . The film thickness was fixed to be about
0.3 μm which is thin enough to rule out the possibility of
unwanted implantation effects.
Figure 1 shows the change in electrical conductivity
plotted against fluence. Prominent electrical degradation
is observed in the fluence range from 10 12 to 10 14 ions/cm 2 ,
and it saturates in the high fluence range above
10 14 ions/cm 2 . This behavior can be understood, if the
damage cross-section of around 7 × 10 -15 cm 2 and electrical
conductivity of damaged region of around 3 × 10 -4 -1 m -1
are assumed. This is demonstrated as a dotted curve in the
figure.
In Fig. 2, the intensity of X-ray diffraction peak ((002)
peak intensity) is plotted as a function of fluence.
A sudden decrease in peak intensity is observed in the
fluence range of around 10 13 ions/cm 2 . The decrease in the
intensity saturates in the high fluence range over about 10 13 -
10 14 ions/cm 2 . This behavior can be understood, if the
damage cross-section of around 1 × 10 -13 cm 2 is assumed.
This is demonstrated as a dotted curve in the figure. The
damage cross-section for electrical conductivity
measurement is smaller than that for XRD measurement,
indicating that the damaged area responsible for electrical
degradation is smaller than that responsible for
crystallographic degradation.
JAEA-Review 2010-065
- 143 -
Part of the present study is the result of “Research of
highly accurate evaluation of radiation damage in advanced
nuclear reactor fuel ceramics” entrusted to “Japan Atomic
Energy Agency” by the Ministry of Education, Culture,
Sports, Science and Technology of Japan (MEXT). Part of
the present work was supported by KAKENHI (21360474).
Electrical Conductivity, σ(Ω −1 m −1 )
10 −3
10 −4
10 −5
10 −6
10 12
10 14
fluence(ions/cm 2 )
10 16
Fig. 1 Electrical conductivity of CeO2 thin films plotted
against fluence of 10 MeV Ni ions. For a dotted
curve, see text.
Normalized Intensity, I/I o
1.4
1.2
1
0.8
0.6
0.4
0.2
0
10 12
10 14
Fluence (ions/cm 2 )
10 16
Fig. 2 Intensity of X-ray diffraction peak normalized by
that of unirradiated CeO 2 thin films plotted against
fluence of 10 MeV Ni ions. For a dotted curve, see
text.