Experimental investigation of neutron irradiation effects on α- alumina nanoparticles in water-based nanofluid for a light water reactor coolant

Abstract

Nanoparticles offer several advantages in terms of heat transfer, stability, safety, and efficiency, making them an attractive option for reactor coolants. The feasibility of using α-alumina (α-Al2O3) nanoparticles as a component of coolant for a light water reactor was investigated under the high neutron flux conditions of a TRIGA Mark II research reactor. To achieve this, highly thermally conductive α-Al2O3 nanoparticles were synthesized using the sol-gel method. X-ray diffraction spectra analysis confirmed the crystal structure and the alpha (α) phase of the sample. The average crystal size was determined to be 55.5 nm. Transmission electron microscope analysis revealed that the nanoparticles had sizes ranging from 40 to 60 nm, although the shape of the particles was irregular. Thermogravimetric analysis indicated a weight loss of less than 0.5% over a temperature range from 30 °C to 1200 °C. Dynamic light scattering showed two intensity peaks at 129.6 nm and 623.2 nm, resulting in a Zeta average (Z) value of 474.9 nm and a polydispersity index of 0.688. In the TRIGA Mark II research reactor, the synthesized nanoparticles were exposed to a thermal neutron flux of 5.28 × 1012 n/cm2/s using a pneumatic transfer irradiation channel (rabbit system). This irradiation resulted in the formation of various activated products, including 28Al, 24Na, and 27Mg, with abundances of 50.5 ± 0.3%, 0.18 ± 0.02%, and 1.59 ± 0.06%, respectively. All of these nuclides are radioactive, with half-lives ranging from minutes to hours. The induced radioactivity in the reactor core area poses a risk of secondary radiation. The physicochemical interaction of these induced products, especially sodium (24Na), with the coolant and other components, is not safe, as sodium is a highly reactive element that can undergo an exothermic reaction with water. These findings suggest that the use of α-Al2O3 in water as a reactor coolant should be further examined from the viewpoints of neutron irradiation effects and the physicochemical interaction of activated products with core materials.