Monte Carlo analysis of nitrided Al-6061-T6 as an alternative fuel holder tube in subcritical reactors

The selection of fuel holder tube material in subcritical reactors is critical for operational safety and long-term efficiency. In this study, a Monte Carlo analysis using the MCNP5 code was conducted to evaluate the impact of replacing Al-6061-T6 with its nitrided variant (Al-6061-T6-N), treated via Plasma Immersion Ion Implantation (PIII), as a structural material for the fuel holder tubes in a low-power subcritical reactor. The results showed that the surface modification does not induce significant changes in the effective multiplication factor or in the neutron and gamma-ray spectra. Likewise, the Ambient dose equivalents measured at various positions around the reactor remained virtually unchanged. These findings suggest that the PIII technique preserves the essential nuclear interaction properties of the material without compromising radiological safety. However, complementary experimental studies are recommended to validate its long-term performance under real operating conditions and radiation-induced aging. • Monte Carlo study was carried out to estimate the impact of using two materials to build the tubes hosting the fuel slugs in a subcritical reactor. • Tube materials were Al-6061-T6 and its nitrided variant (Al-6061-T6-N). • The nitrided layer was modeled with a 20 μm depth and 20% nitrogen incorporation by weight, preserving total geometry. • There is not significant difference in the effective multiplication factor (rate ≈ 0.12%) neither the neutron and γ-rays spectra. • There are not significant differences in the Ambient dose equivalent outside the reactor, due to neutrons and γ-rays. • Surface nitriding via PIII preserves neutronic and shielding properties, while offering improved corrosion resistance, supporting its use in research reactors.