Evolution of thermo-physical properties and annealing of fast neutron irradiated boron carbide

Evolution of thermo-physical properties and annealing of fast neutron irradiated boron carbide

Boron carbide is widely used as a neutron absorber in most nuclear reactors, in particular in fast neutron ones. The irradiation leads to a large helium production (up to 1022/cm3) together with a strong decrease of the thermal conductivity. In this paper, we have performed thermal diffusivity measu...

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Bibliographic Details
Published in:Journal of nuclear materials Vol. 500; pp. 166 - 175
Main Authors: Gosset, Dominique, Kryger, Bernard, Bonal, Jean-Pierre, Verdeau, Caroline, Froment, Karine
Format: Journal Article
Language:English
Published: Amsterdam Elsevier B.V 01-03-2018
Elsevier BV
Elsevier
Subjects:
Annealing
Boron
Boron carbide
Control rods
Defects
Diffraction
Heat conductivity
Heat transfer
Heat treatments
Helium
High temperature
Irradiation
Microstructure
Neutron absorber
Nuclear Experiment
Nuclear reactors
Nuclear Theory
Physical properties
Physics
Reactors
Restoration
Rods
Sintering
Strain relaxation
Studies
Thermal conductivity
Thermal diffusivity
X-ray diffraction
Thermal conductivity
Neutron absorber
Microstructure
Heat treatments
Boron carbide
neutron absorber
microstructure
thermal conductivity
heat treatments
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Summary:Boron carbide is widely used as a neutron absorber in most nuclear reactors, in particular in fast neutron ones. The irradiation leads to a large helium production (up to 1022/cm3) together with a strong decrease of the thermal conductivity. In this paper, we have performed thermal diffusivity measurements and X-ray diffraction analyses on boron carbide samples coming from control rods of the French Phenix LMFBR reactor. The burnups range from 1021 to 8.1021/cm3. We first confirm the strong decrease of the thermal conductivity at the low burnup, together with high microstructural modifications: swelling, large micro-strains, high defects density, and disordered-like material conductivity. We observe the microstructural parameters are highly anisotropic, with high micro-strains and flattened coherent diffracting domains along the (00l) direction of the hexagonal structure. Performing heat treatments up to high temperature (2200 °C) allows us to observe the material thermal conductivity and microstructure restoration. It then appears the thermal conductivity healing is correlated to the micro-strain relaxation. We then assume the defects responsible for most of the damage are the helium bubbles and the associated stress fields.
ISSN:0022-3115
1873-4820
DOI:10.1016/j.jnucmat.2017.11.027