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Title: A thermal conductivity model for U-­Si compounds

Abstract

U 3Si 2 is a candidate for accident tolerant nuclear fuel being developed as an alternative to UO 2 in commercial light water reactors (LWRs). One of its main benefits compared to UO 2 is higher thermal conductivity that increases with temperature. This increase is contrary to UO 2, for which the thermal conductivity decreases with temperature. The reason for the difference is the electronic origin of thermal conductivity in U 3Si 2, as compared to the phonon mechanism responsible for thermal transport in UO 2. The phonon thermal conductivity in UO 2 is unusually low for a fluorite oxide due to the strong interaction with the spins in the paramagnetic phase. The thermal conductivity of U 3Si 2 as well as other U-­Si compounds has been measured experimentally [1-­4]. However, for fuel performance simulations it is also critical to model the degradation of the thermal conductivity due to damage and microstructure evolution caused by the reactor environment (irradiation and high temperature). For UO 2 this reduction is substantial and it has been the topic of extensive NEAMS research resulting in several publications [5, 6]. There are no data or models for the evolution of the U 3Si 2 thermalmore » conductivity under irradiation. We know that the intrinsic thermal conductivities of UO 2 (semi-conductor) and U 3Si 2 (metal) are very different, and we do not necessarily expect the dependence on damage to be the same either, which could present another advantage for the silicide fuel. In this report we summarize the first step in developing a model for the thermal conductivity of U-­Si compounds with the goal of capturing the effect of damage in U 3Si 2. Next year, we will focus on lattice damage. We will also attempt to assess the impact of fission gas bubbles.« less

Authors:
 [1];  [2]
  1. Idaho National Lab. (INL), Idaho Falls, ID (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Nuclear Energy (NE)
OSTI Identifier:
1342838
Report Number(s):
LA-UR-16-27736
TRN: US1701909
DOE Contract Number:
AC52-06NA25396
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; URANIUM SILICIDES; THERMAL CONDUCTIVITY; ACCIDENT-TOLERANT NUCLEAR FUELS; WATER MODERATED REACTORS; WATER COOLED REACTORS; SIMULATION

Citation Formats

Zhang, Yongfeng, and Andersson, Anders David Ragnar. A thermal conductivity model for U-­Si compounds. United States: N. p., 2017. Web. doi:10.2172/1342838.
Zhang, Yongfeng, & Andersson, Anders David Ragnar. A thermal conductivity model for U-­Si compounds. United States. doi:10.2172/1342838.
Zhang, Yongfeng, and Andersson, Anders David Ragnar. Thu . "A thermal conductivity model for U-­Si compounds". United States. doi:10.2172/1342838. https://www.osti.gov/servlets/purl/1342838.
@article{osti_1342838,
title = {A thermal conductivity model for U-­Si compounds},
author = {Zhang, Yongfeng and Andersson, Anders David Ragnar},
abstractNote = {U3Si2 is a candidate for accident tolerant nuclear fuel being developed as an alternative to UO2 in commercial light water reactors (LWRs). One of its main benefits compared to UO2 is higher thermal conductivity that increases with temperature. This increase is contrary to UO2, for which the thermal conductivity decreases with temperature. The reason for the difference is the electronic origin of thermal conductivity in U3Si2, as compared to the phonon mechanism responsible for thermal transport in UO2. The phonon thermal conductivity in UO2 is unusually low for a fluorite oxide due to the strong interaction with the spins in the paramagnetic phase. The thermal conductivity of U3Si2 as well as other U-­Si compounds has been measured experimentally [1-­4]. However, for fuel performance simulations it is also critical to model the degradation of the thermal conductivity due to damage and microstructure evolution caused by the reactor environment (irradiation and high temperature). For UO2 this reduction is substantial and it has been the topic of extensive NEAMS research resulting in several publications [5, 6]. There are no data or models for the evolution of the U3Si2 thermal conductivity under irradiation. We know that the intrinsic thermal conductivities of UO2 (semi-conductor) and U3Si2 (metal) are very different, and we do not necessarily expect the dependence on damage to be the same either, which could present another advantage for the silicide fuel. In this report we summarize the first step in developing a model for the thermal conductivity of U-­Si compounds with the goal of capturing the effect of damage in U3Si2. Next year, we will focus on lattice damage. We will also attempt to assess the impact of fission gas bubbles.},
doi = {10.2172/1342838},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Feb 02 00:00:00 EST 2017},
month = {Thu Feb 02 00:00:00 EST 2017}
}

Technical Report:

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  • Thermal conductivity, electrical resistivity, total hemispherical emittance ( epsilon /sub t/), and normal spectral emittance ( epsilon /sub 0.65 mu /) data were obtained from rod specimens of UO/sub 2/, UC, U/sub 0.5/C, and ThC/sub 2/ im the temperature range 1100 to 2400 deg K. The results are presented in graphs amd tables. (auth)
  • As part of the Reduced Enrichment Research and Test Reactor (RERTR) program, high density uranium compounds are being evaluated as possible replacements for the fuels currently in use. U/sub 3/Si and U/sub 3/Si/sub 2/ powders dispersed in an Al matrix and roll bonded within 6061 Al alloy clad have performed well under irradiation in the ORR. A consideration of the heats of reaction between the silicides and the Al components of a reactor fuel plate has now been addressed. By following standard quantitative differential thermal analysis (DTA) procedures, it has been demonstrated that neither silicide shows any measurable heat ofmore » reaction until the solidus temperature of 6061 (582/sup 0/C) is exceeded. On heating, the exothermic reaction is quenched by the endothermic change of state as the Al species melt. All detectable events take place in the temperature regime from approx. 580 to approx. 660/sup 0/C. The heats of reaction per gram of fuel ranged from 304 +- 18 J for samples with 32 vol. % U/sub 3/Si/sub 2/ in the fuel zone to 486 +- 54 J for samples containing 45 vol. % U/sub 3/Si in the fuel zone. 6 references, 11 figures, 7 tables.« less
  • An experimental study was made to decide upon the advantages and drawbacks of the different methods and reagents employed in the metallography of U-Si alloys. It has been observed that all samples thermally treated to the epsilon-phase undergo a coalescence of the U/sub 3/Si/sub 2/ particles. The coalescence decreases the surface available for reaction and consequently the reaction rate. The growth of the U/sub 3/Si/sub 2/ phase particles was determined as a function of time and temperature. To obtain samples with nuclei sufficiently isolated so that the U/sub 3/Si rings will not interfere their respective growth, the conditions that regulatemore » coalescence, Si content and thermal treatment, were determined. Data rel1tive to the growth of the U/sub 3/ Si phase-rings were obtained. Curves relating growth, time, and temperature are presented. The parameters that define the diffusion regulated reaction can be deduced from these curves. (auth)« less
  • This paper describes the primary physical models that form the basis of the DART model for calculating irradiation-induced changes in the thermal conductivity of aluminium dispersion fuel. DART calculations of fuel swelling, pore closure, and thermal conductivity are compared with measured values.