Research

Dose Rate Dependence of Radiation Induced Conductivity
for Hydrogen-Doped Perovskite-type Ceramics
Dose rate dependence of radiation induced conductivity(RIC) of hydrogen doped yttrium-doped perovskite-type
barium-cerium oxide ceramics (BaCe0.9Y0.1O3-δ) wasinvestigated under 1.8 MeV electron irradiation within doserate of 10 - 1000 Gy/s at temperature of 473 K. For the dose
rates below 200 Gy/s, the RIC of the H-doped BaCe0.9Y0.1O3-δwas higher by one order of magnitude than that of theH-undoped one. The results may show that the RIC takes
place due to hydrogen diffusion as well as electronic
excitation, enhanced by ionizing effects. For the dose rate
range 300 to 1000 Gy/s, the RIC of H-doped BaCe0.9Y0.1O3-δ
is similar to that of H-undoped one. The radiation enhanced
diffusion of constitutive oxygen dominates for the RIC.
So far, it has been reported that the electrical properties
of insulating materials such as oxide ceramics are dynamicallychanged by several radiation induced phenomena [1, 2]. It
will be predicted that the radiation induced phenomena arefurther enhanced by behavior of hydrogen isotopes trappedin the insulating materials during long term D - T discharge.
In the present study, to clarify the changes in proton andionic conductions by electronic excitation effects, electrical,
proton and ion conductivities of BaCe0.9Y0.1O3-δ, heated attemperature of 473 K, were in-situ measured with changing
dose rates of 10 - 1000 Gy/s using 1.8 MeV electron beams
from Van de Graaff at Euratom/CIEMAT.
Fig. 1 shows radiation induced conductivity, σRIC, for
H-doped BaCe0.9Y0.1O3-δ as a function of ionizing dose rate
for 200, 500 and 1000 Gy/s, respectively, during electron
irradiation. The RIC at 200 Gy/s increases about 23 times
higher, as compared base conductivity, σBC, without radiation.
The RIC in the initial dose is similar to that in the final one
which means that the irradiation time is 60 min. On the other
hand, the RIC in the initial at 500 and 1000 Gy/s is respectively
about 293 and 3485 times as much as those before irradiation,
whereas the RIC in the final one changes to be respectively
about 130 and 5484 times as much as those after irradiation.
The degradation of σRIC and σBC is possibly called Radiation
Induced Electrical Degradation (RIED) which is generally
considered to occur with an electric field during irradiation.
The RIED phenomenon has been associated withdisplacement damage and radiation induced impuritydiffusion. In the present study the mobilities of dopant Y

Fig. 2 Dose rate dependence of ΔRIC (ΔRIC=σRIC -σBC).
atoms, constitutive oxygen, barium and cerium ions andimpurities, and in particular hydrogen atoms, may beenhanced under the present irradiation conditions at elevatedtemperature of 473 K. The dose rate dependences of σRIC
and σBC for H-undoped BaCe0.9Y0.1O3-δ show the same
results with that for H-doped one, although the absolutevalues are different.
Fig. 2 shows dose rate dependence of ΔRIC (ΔRIC=σRIC-σBC), which means the increment of the RIC, obtained bysubtracting the base conductivity from the RIC, for H-doped
and -undoped BaCe0.9Y0.1O3-δ respectively in the final doses
during electron irradiation at 473 K. For dose rates under 200
Gy/s, the ΔRIC of H-doped BaCe0.9Y0.1O3-δ is about oneorder magnitude higher than that of H-undoped one. The
difference of the ΔRIC between H-doped and -undoped
BaCe0.9Y0.1O3-δ may be caused by enhancement of diffusionof H due to ionizing irradiation. On the other hand, for thedose rates above 300 Gy/s, the ΔRIC of H-doped
BaCe0.9Y0.1O3-δ was close to that of H-undoped one. The
coincident of the ΔRIC indicate that the charge carrier for theconductivity is not hydrogen but constitutive atoms in thematrix, mainly oxygen. The mobility of oxygen ions in
BaCe0.9Y0.1O3-δ generally starts at elevated temperature
above 973 K. The diffusion of oxygen ions may be enhancedby ionizing effects with high dose rates above 300 Gy/s even
if the temperature is 473 K.
References[1] B. Tsuchiya, A. Moroño, S. M. González, E. R. Hodgson,S. Nagata, K. Toh and T. Shikama, J. Nucl. Mater. 386-388,342-344, (2009).
[2] B. Tsuchiya, T. Shikama, S. Nagata, K. Toh, M. Narui andM. Yamazaki, J. Nucl. Mater. 367-370, 1073-1078 (2007).
Key Words
Radiation Induced Conductivity, Proton Conducting Perovskitetype Oxide Ceramics, Radiation Enhanced Diffusion
Contact toTatsuo Shikama (Nuclear Science Materials Division)e-mail: shikama@imr.tohoku.ac.jp

Fig. 1 Radiation induced conductivity (RIC) against irradiation
time at 200, 500, and 1000 Gy/s.

KINKEN Research Highlights 2009 IMR

Advanced Nuclear Energy Materials

35ResearchObservation of One-dimensional Motion of Self-interstitial Atom
Clusters in A533B Steel for Nuclear Reactors
Self-interstitial atom (SIA) clusters in practical steel
A533B used for nuclear power plants were shown to cause
one-dimensional (1D) motion under electron irradiation.
Frequency of 1D motion was greatly reduced at elevatedtemperatures. Interstitial atoms, namely, carbon, nitrogenand oxygen were thought to segregate on SIA clusters andto pin them down.
Recent molecular dynamics simulations and experimental
observation with TEM revealed that SIA clusters in puremetals cause 1D motion with low activation energy. It has
been pointed out that 1D motion of SIA clusters plays a vitalrole in microstructural evolution of materials under irradiation,such as swelling of materials due to void growth (Fig. 1).
Therefore, it is important to elucidate how actively SIA
clusters cause 1D motion in materials used for nuclear
reactors under the service conditions. It is also important tounderstand to what extent 1D motion affects themicrostructural evolution.
The 1D motion of SIA clusters is observed frequently witha high voltage electron microscope (HVEM): electron
irradiation promotes 1D motion. Experimental observations
have also shown that impurities and alloying elements reduce
the frequency and distance of 1D motion [1]: solute/impurity
atoms are considered to pin down SIA clusters. Moreover, it
has been revealed that the effects of impurities and solutes
appear even with very small concentrations [1]. Judging fromthese findings, one may simply infer that 1D motion hardly
occurs in commercial materials containing larger amounts ofalloying elements.
By means of in-situ observations using an HVEM, westudied 1D motion of SIA clusters in A533B steel used forreactor pressure vessels (RPV) in nuclear power plants.
Electron irradiation and in-situ observations were carried out
by using JEMARM-1250 (JEOL Ltd.) operated at anacceleration voltage of 1250kV. The irradiation was done atroom temperature or 563K; 563K is close to the temperature
at which A533B steels are used at nuclear reactors. The
electron flux was 3x1024e/m2s; this corresponds to a damage

Cascade damage
Interstitial cluster

1D motion
Vacancies

rate of 2x10-2dpa/s.
Fig. 2 shows that 1D motion certainly occurred in theA533B steel under electron irradiation at room temperature[2]. The direction of 1D motion was along <111>, and the
distance of most 1D motion was less than 10 nm. On theother hand, 1D motion was greatly suppressed under electron
irradiation at 563K. We defined the motion frequency as theaverage number of 1D motion observed per single SIA cluster
during unit time. The motion frequencies were 1.7x10-2 and
0.1x10-2 s-1 at room temperature and 563 K, respectively.
The effect of annealing on 1D motion at room temperature
was investigated to understand why the frequency is low at
563K. SIA clusters became less mobile after annealing at
473K and above. Although the annealing reduced the mobilityof clusters which had been formed before the annealing, theannealing effect was not detected on clusters which wereformed after the annealing. SIA clusters which had becomeless mobile due to annealing recovered their mobility byprolonged irradiation at room temperature. Accordingly, theatoms of interstitial elements, namely carbon, nitrogen andoxygen were considered to segregate on SIA clusters
considerably and to pin them down at 563K. These results
suggest that 1D motion is possible to occur in A533B underirradiation with neutrons depending on the irradiation
condition.
Reference[1] Y. Satoh, H. Matsui, T. Hamaoka, Phys. Rev., B77, 94135(2008).
[2] T. Hamaoka, Y. Satoh, H. Matsui, submitted to J. Nucl.
Mater.
Key Words
Radiation Damage, Defect Clusters, Void Swelling

VoidGrain boundary

Fig. 1 ‘Production bias mechanism’ for void swelling undercascade damage condition.

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Fig. 2 In-situ observation of 1D motion of SIA clusters inA533B under electron irradiation at room temperature.

Advanced Nuclear Energy Materials

Contact toYuhki Satoh (Nuclear Materials Engineering Division)e-mail: ysatoh@imr.tohoku.ac.jp

IMR KINKEN Research Highlights 2009

ResearchDevelopment of Hydride Neutron Absorber
Hydride neutron absorbers have been proposed to be
used in Fast Breeder Reactor. Demonstration of pellet
fabrication have been successfully done. Irradiation behaviorof hydride materials were tested in the fast experimental
reactor, JOYO.
A metal-hydride has very high hydrogen atom density, whichis equivalent to that of liquid water. Fast neutrons in nuclear
reactors are efficiently moderated and are absorbed in the metalhydride. The Hf hydride and Zr-Gd hydride are considered as
neutron absorber in FBR (Fast Breeder Reactor).
The development program of hydride neutron absorber
was started in Jun 2006. It was accepted as an innovative
nuclear research and development program of Ministry ofEducation, Culture, Sports, Science and Technology of Japan.
The program was accomplished in March 2009.
In this study the core design is performed to examine its
characteristics and to evaluate cost reduction effect. One ofthe major R&D items of the present the program is developmentof hydride pellet, which is used in the reactor core[1]. Figure 1
shows the Hf hydride pellet and Zr-Gd hydride pellet. The
slight barrel-shaped transformations were observed, since
the pellets were expanded by hydrogen absorption. The
transformations can be removed by grinding their sides [2,3].
Irradiation test of hydride neutron absorber was conductedin the fast experimental reactor, JOYO, at Japan Atomic Energy
Association (JAEA), where Hf hydride disks and Zr-Gd hydride
disks were irradiated with neutron fluence of 2.92×1021(n/cm2)(E>0.1MeV) and 3.25×1021(n/cm2)(E>0.1MeV) for Hf hydrideones and Zr-Gd hydride disks respectively. Irradiation
temperatures are 590°C and 580°C for Hf hydride disks andZr-Gd hydride disks, respectively. After irradiation, the capsulecontaining of the hydride disks was tested by X-ray CT
Inspection method (Fig.2). The result show that the capsule
was irradiated with keeping it’s integrity. The chipping and thecracking of the disks were not found in the hydrides.
After the non-destructive examinations, the capsule wascut for sampling of the irradiated hydride disks for destructive
examinations; measurement of weight, metallographic test,
X-ray diffraction test, measurement of thermal diffusivity. No
swelling was found in the disks. Figure 3 shows the results ofthermal diffusivity test. Thermal diffusivity data of un-irradiatedsample (blue diamond symbols) are also plotted in Fig.3 forcomparison with irradiated data (red rectangular symbols).
Figure 3 shows that no effect of neutron irradiation on thermal

Hf hydride disk
Fig. 2 X-ray CT image of irradiated capsule

Fig. 3 comparison of thermal diffusivity data of irradiated Hfhydride disk with un-irradiated one
diffusivity of Hf hydride. This is the first experimental result of
thermal diffusivity of irradiated Hf hydride. In the case of oxide(e.g. UO2), it is well known that the thermal diffusivity decreases
with the increase of the accumulated neutron irradiation dose
because of radiation damage. The present results of thermal
diffusivity of irradiated Hf hydride are noteworthy.
References[1] T. Iwasaki and K. Konashi, ‘Development of Hydride
Absorber for Fast Reactor - Application of hafnium hydride tocontrol rod of large fast reactor –‘, to be published in J. Nucl.
Sci. Technol..
[2] K. Konashi et al., ‘Study on an innovative Fast Reactor
utilizing Hydride Neutron Absorber’, Proc. of International
Congress on Advances in Nuclear Power Plants (ICAPP2008),
June.8-12, 2008, Anaheim, USA.
[3] Y. Kitano et al., ‘Fabrication and mechanicalcharacterization of zirconium and gadolinium hydrides’, J.
Nucl. Mater. 389 (2009) 170–172.
Key Words
Hydride, Nuclear Material, Irradiation Test

Hf hydride pellet

Zr-Gd hydride pellet

Fig. 1 Hydride neutron absorber pellets

KINKEN Research Highlights 2009 IMR

Contact toKenji Konashi (International Research Center for Nuclear
Materials Science)e-mail: konashi@imr.tohoku.ac.jp

Advanced Nuclear Energy Materials

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