Abstract
The microstructure of Al/B4C metal matrix composites (MMCs) used as neutron absorbers in both dry storage casks and wet storage pools of spent nuclear fuel was analyzed by SEM and TEM. A polishing method of a focused Ga+ ion beam was used to obtain an ideal sample surface with very low roughness, which was used to statistically analyze the distribution characteristics and size factor of B4C particles in the aluminum matrix. The area of B4C particles mainly ranged from 0 to 0.5 μm2, which was the proportion of 64.29%, 86.99% and 76.86% of total statistical results for the Al-15%B4C, Al-25%B4C and Al-30%B4C MMCs, respectively. The average area of B4C particles in the Al-15%B4C, Al-25%B4C and Al-30%B4C MMCs were about 1.396, 0.528 and 1.183 μm2, respectively. The nanoscale precipitates were analyzed by the element mappings in scanning transmission electron microscopy (STEM) mode and electron energy loss spectroscopy (EELS) mode, which included elliptic alloy precipitates with elemental Cu, Cr, Fe and Si, except for Al, and B4C nanoparticles with polygonal shape. The interface characteristics showed that the (021) crystal plane of B4C particle and (111) crystal plane of aluminum matrix grew together. The lattice misfit was about 1.68% for (111)Al//(021)B4C. The corrosion properties and corresponding mechanism of Al/B4C MMCs were investigated in an aqueous solution with 5000 ppm boric acid at 100 °C and atmospheric pressure, which showed that the mass increment rate was first decreased with increasing corrosion time and then increased.
Highlights
Since the long-term integrity of a thermal neutron poison is essential for effective criticality control of used nuclear fuel during storage, boron containing alloys or composites have been used in both used fuel pool storage racks and dual-purpose canisters and casks
The corrosion properties and corresponding mechanism of Al/B4 C metal matrix composites (MMCs) were investigated in an aqueous solution with 5000 ppm boric acid at 100 ◦ C and atmospheric pressure, which showed that the mass increment rate was first decreased with increasing corrosion time and increased
Because Al/B4 C MMCs have high thermal conductivity and thermal stability, they are tremendously beneficial for dry storage casks that will be loaded with mixed oxide (MOX) fuel and highly enriched fuel
Summary
Since the long-term integrity of a thermal neutron poison is essential for effective criticality control of used nuclear fuel during storage, boron containing alloys or composites have been used in both used fuel pool storage racks and dual-purpose (storage/transportation) canisters and casks. MMCs, such as helium bubbles in Al matrix [4], amorphization occurred in severe conditions [10], and interfacial microstructure in Al/B4 C [11]; (3) The degradation mechanism including irradiation damage [5], boron leaching, corrosion and mechanical damage [12]; (4) The discussion of preparation process, mechanical properties [13,14,15,16], microstructural characteristics [17]. Despite these extensive investigations, there are still some questions associated with the microstructure characteristics in the Al/B4 C MMCs that need to be answered. The corrosion properties and corresponding mechanism were investigated in an aqueous solution with 5000 ppm boric acid at 100 ◦ C and atmospheric pressure
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