A group of Mexican researchers from the National Institute of Nuclear Research, the Autonomous University of Zacatecas and the Technological Institute of Monterrey has proposed replacing aluminum tubes that house nuclear fuel in a subcritical reactor with similar tubes made of stainless steel. Their study aimed to improve reactor reliability and reduce radiation exposure for personnel.
A subcritical reactor is a safe type of nuclear facility where the nuclear fuel (uranium) cannot independently maintain a chain reaction and requires an external neutron source, such as a plutonium-beryllium generator. In these reactors, fuel is enclosed in thin-walled tubes made of the Al-6061-T6 aluminum alloy, which was chosen for its lightness, strength and minimal impact on the neutron flux. However, in real operating conditions where water is used as a neutron moderator and reflector, aluminum is subjected to intense corrosion, especially in the presence of impurities and under the influence of radiation. This leads to the formation of an oxide film, a decrease in the strength of the material, the development of cracks and the risk of leakage in the reactor.
To avoid these problems, the researchers proposed using stainless steel grade 316L, which is highly resistant to corrosion and has good mechanical properties. To that end, they created a precise computer model of the NC-9000 reactor, which is being used in Mexico for educational and research purposes. The model compared two cases: one using aluminum tubes and one using steel tubes, while all other reactor parameters remained the same. The scientists analyzed how the replacement of the material affected the neutron and gamma radiation flux, as well as the radiation levels in characteristic zones around the facility.
The model showed that the use of stainless steel significantly reduces the neutron flux, especially in the thermal range, while having a negligible effect on gamma radiation, which makes it possible to maintain experimental accuracy. Crucially, the scientists’ findings indicate that stainless steel increases structural integrity and reduces background radiation around the reactor: neutron doses are reduced by up to 77% and gamma doses get nearly halved. These figures indicate a marked improvement in personnel safety.
Therefore, despite a partial reduction in neutron activity, 316L stainless steel can become a reliable and promising alternative to aluminum. In the future, the Mexican researchers propose conducting practical tests with steel tubes, studying the potential activation of their components during irradiation and assessing the impact of this process on the level of gamma radiation near the reactor core during long-term operation.
