Thermal and Mechanical Properties of Hf Hydrides with Various Hydrogen Content
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1215-V18-02
Thermal and Mechanical Properties of Hf Hydrides with Various Hydrogen Content Ken Kurosaki1, Masato Ito1,*, Yuki Kitano1, Hiroaki Muta1, Masayoshi Uno2, Kenji Konashi3, and Shinsuke Yamanaka1,2 1 Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan 2
Research Institute of Nuclear Engineering, Fukui University, 3-9-1 Bunkyo, Fukui 910-8507, Japan 3
Institute for Materials Research, Tohoku University, 2145-2, Narita, Oarai-machi, Ibaraki 311-1313, Japan *
Present address: Mitsubishi Materials Corporation
ABSTRACT Fine bulk samples of delta-phase Hf hydride with various hydrogen contents (CH) ranging from 1.62 to 1.72 in the atomic ratio (H/Hf) were prepared, and their thermal and mechanical properties were characterized. In the temperature range from room temperature to around 650 K, the heat capacity and thermal diffusivity of the samples were measured and the thermal conductivity was evacuated. The elastic modulus was calculated from the measured sound velocity. The Vickers hardness was measured at room temperature. Effects of CH and/or temperature on the properties of Hf hydrides were discussed. At room temperature, the thermal conductivity values of the Hf hydrides were 23 Wm-1K-1. The Young’s and shear moduli and the Vickers hardness of Hf hydride decreased with increasing CH.
INTRODUCTION Although boron carbide (B4C) is currently expected as neutron control materials for fast reactors (FRs), the life time of the B4C control rods is restricted by pellet-cladding mechanical interaction failure due to the helium gas swelling which is caused by the following nuclear reaction: 10 B(n, α )7 Li . In order to prolong the life time of the control rods, we have proposed Hf hydrides as the neutron control materials [1], because no helium gas is produced during neutron absorption. The nuclear reaction is expressed as follows: 177 Hf (n, γ )178 Hf (n, γ )179 Hf (n, γ )180 Hf . Since hydrogen can moderate fast neutrons and Hf has large cross sections for thermal neutron
capture, Hf hydrides would be an effective neutron control materials in FRs. In addition, since the daughter nuclides 178Hf and 179Hf also have large cross sections for thermal neutron capture as well as the parent nuclide 177Hf, Hf hydrides would absorb neutrons for more than 40 years [1]. When utilizing Hf hydrides as long-life neutron control materials with no helium production in FRs, it is very important to understand their thermal and mechanical properties. Although the physical properties of Ti hydrides [2] and Zr hydrides [3] have been widely examined, those of Hf hydrides have been scarcely reported until now. Recently, the authors succeeded to synthesis fine bulk samples of Hf hydrides with various hydrogen contents and evaluated their thermal and mechanical properties at elevated temperatures up to around 650 K [4,5]. In the present paper, we will summarize our progress in understanding the effects of CH and/or temperature on the thermal and mechanical properties of Hf hydrides.
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