Investigation of the properties of aluminum tube used in Thailand research reactor TRR-1/M1

Thailand research reactor, TRR-1/M1, operated approximately at 1,200 kWth, which produced maximum neutrons flux of 8×10¹³n/cm².sec and temperature of ∼400°C at hottest spot. This paper presents the material degradation analyses of an aluminum (Al6061) tube used as a pneumatic transferred irradiation tube at position G33 in the TRR-1/M1 reactor core from 1977 to 2005. The analyses consisted of oxide characterization and radiation hardening measurement. The oxide characterization was done using XRD grazing angle technique for phase identification, and SEM for surface morphology and cross-section investigation. The radiation hardening was evaluated through Vicker-hardness measurement. Results showed that oxide on the aluminium tube consisted of three layers; a transition layer, a Al oxide layer of Bayerite (Al(OH)₃) or Gibbsite (Al₂O₃.3H₂O), and a thin layer of small grains of Quartz (SiO₂). The results revealed that neutron-captured reaction of Al produced Si, which can cause changes in material properties from loss of Al content in bulk material. The hardness test showed that Al tube specimens were softer than control specimens. Overall outcome of the study explained the major degradation mechanisms in the reactor core, which led to suggestions on maintenance and service life time of the materials for safe operation of the reactor. (paper)