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Title: Dense nanocrystalline UO 2+ x fuel pellets synthesized by high pressure spark plasma sintering

Authors:
ORCiD logo [1]; ORCiD logo [1];  [1];  [1];  [1]
  1. Department of Mechanical, Aerospace, and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy New York
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1408189
Grant/Contract Number:
NE0008440
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of the American Ceramic Society
Additional Journal Information:
Journal Volume: 101; Journal Issue: 3; Related Information: CHORUS Timestamp: 2018-01-02 04:55:10; Journal ID: ISSN 0002-7820
Publisher:
Wiley-Blackwell
Country of Publication:
United States
Language:
English

Citation Formats

Yao, Tiankai, Scott, Spencer M., Xin, Guoqing, Gong, Bowen, and Lian, Jie. Dense nanocrystalline UO 2+ x fuel pellets synthesized by high pressure spark plasma sintering. United States: N. p., 2017. Web. doi:10.1111/jace.15289.
Yao, Tiankai, Scott, Spencer M., Xin, Guoqing, Gong, Bowen, & Lian, Jie. Dense nanocrystalline UO 2+ x fuel pellets synthesized by high pressure spark plasma sintering. United States. doi:10.1111/jace.15289.
Yao, Tiankai, Scott, Spencer M., Xin, Guoqing, Gong, Bowen, and Lian, Jie. 2017. "Dense nanocrystalline UO 2+ x fuel pellets synthesized by high pressure spark plasma sintering". United States. doi:10.1111/jace.15289.
@article{osti_1408189,
title = {Dense nanocrystalline UO 2+ x fuel pellets synthesized by high pressure spark plasma sintering},
author = {Yao, Tiankai and Scott, Spencer M. and Xin, Guoqing and Gong, Bowen and Lian, Jie},
abstractNote = {},
doi = {10.1111/jace.15289},
journal = {Journal of the American Ceramic Society},
number = 3,
volume = 101,
place = {United States},
year = 2017,
month =
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on November 1, 2018
Publisher's Accepted Manuscript

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  • Spark plasma sintering (SPS) technique has been attempted to prepare dense lithium ion conductors composed of nanostructured Li{sub 1.4}Al{sub 0.4}Ti{sub 1.6}(PO{sub 4}){sub 3} with the NASICON-type structure. Typical 100% of theoretical density in the pellets was achieved for the sample by SPS at 650 deg. C, a much lower temperature compared to the solid-state sintering process. The ionic conductivity of 1.12 x 10{sup -3} S/cm, the highest one for inorganic Li{sup +}-ion conductors as reported up to date was obtained at 25 deg. C with an activation energy (E{sub a}) of 0.25 eV. The enhancement in ionic conductivity of themore » SPS pellets was supposed mainly due to the decrease in the particle size as well as the extremely high density of the samples.« less
  • Uranium dioxide (UO2) is the most common fuel material in commercial nuclear power reactors. Despite its numerous advantages such as high melting point, good high-temperature stability, good chemical compatibility with cladding and coolant, and resistance to radiation, it suffers from low thermal conductivity that can result in large temperature gradients within the UO2 fuel pellet, causing it to crack and release fission gases. Thermal swelling of the pellets also limits the lifetime of UO2 fuel in the reactor. To mitigate these problems, we propose to develop novel UO2 fuel with uniformly distributed carbon nanotubes (CNTs) that can provide high-conductivity thermalmore » pathways and can eliminate fuel cracking and fission gas release due to high temperatures. CNTs have been investigated extensively for the past decade to explore their unique physical properties and many potential applications. CNTs have high thermal conductivity (6600 W/mK for an individual single- walled CNT and >3000 W/mK for an individual multi-walled CNT) and high temperature stability up to 2800°C in vacuum and about 750°C in air. These properties make them attractive candidates in preparing nano-composites with new functional properties. The objective of the proposed research is to develop high thermal conductivity of UO2–CNT composites without affecting the neutronic property of UO2 significantly. The concept of this goal is to utilize a rapid sintering method (5–15 min) called spark plasma sintering (SPS) in which a mixture of CNTs and UO2 powder are used to make composites with different volume fractions of CNTs. Incorporation of these nanoscale materials plays a fundamentally critical role in controlling the performance and stability of UO2 fuel. We will use a novel in situ growth process to grow CNTs on UO2 particles for rapid sintering and develop UO2-CNT composites. This method is expected to provide a uniform distribution of CNTs at various volume fractions so that a high thermally conductive UO2-CNT composite is obtained with a minimal volume fraction of CNTs. The mixtures are sintered in the SPS facility at a range of temperatures, pressures, and time durations so as to identify the optimal processing conditions to obtain the desired microstructure of sintered UO2-CNT pellets. The second objective of the proposed work is to identify the optimal volume fraction of CNTs in the microstructure of the composites that provides the desired high thermal conductivity yet retaining the mechanical strength required for efficient function as a reactor fuel. We will systematically study the resulting microstructure (grain size, porosity, distribution of CNTs, etc.) obtained at various SPS processing conditions using optical microscopy, scanning electron microscopy (SEM), and transmission electron microscope (TEM). We will conduct indentation hardness measurements and uniaxial strength measurements as a function of volume fraction of CNTs to determine the mechanical strength and compare them to the properties of UO2. The fracture surfaces will be studied to determine the fracture characteristics that may relate to the observed cracking during service. Finally, we will perform thermal conductivity measurements on all the composites up to 1000° C. This study will relate the microstructure, mechanical properties, and thermal properties at various volume fractions of CNTs. The overall intent is to identify optimal processing conditions that will provide a well-consolidated compact with optimal microstructure and thermo-mechanical properties. The deliverables include: (1) fully characterized UO2-CNT composite with optimal CNT volume fraction and high thermal conductivity and (2) processing conditions for production of UO2-CNT composite pellets using SPS method.« less
  • Nanostructured tungsten composites were fabricated by spark plasma sintering of nanostructured composite powders. The composite powders, which were synthesized by mechanical milling of tungsten and Ni-based alloy powders, are comprised of alternating layers of tungsten and metallic glass several hundred nanometers in size. The mechanical behavior of the nanostructured W composite is similar to pure tungsten, however, in contrast to monolithic pure tungsten, some macroscopic compressive plasticity accompanies the enhanced maximum strength up to 2.4 GPa by introducing reinforcement. As a result, we have found that the mechanical properties of the composites strongly depend on the uniformity of the nano-grainedmore » tungsten matrix and reinforcement phase distribution.« less