Aluminium alloy selection for use as structural material in research reactors

Information on a range of aluminium alloys commonly used in the construction of research, experimental or production reactors (series 5XXX and 6XXX)) has been reviewed to assess their capability to sustain a full 40 years life period of use as RPV, reflector tank or other core component material, taking into account their corrosion resistance, fracture properties and irradiation damage. The corrosion behaviour of the studied alloys is acceptable when used in nuclear grade water; they do not suffer of pitting corrosion, crevice corrosion or stress corrosion cracking (SCC). However, in certain conditions they may be susceptible to intergranular corrosion. Based on the available published information, it could be concluded that the alloy 6061-T6 would be the most suitable material to be employed in research reactor conditions (maximum working temperature 120 o C, normal radiation level, water flow, etc.) and sustain 40 years of service if a correct water control is assured. For working temperatures around 60 o C, 6061/T6 alloy would undergo a moderate irradiation hardening degree and show good ductility retention for over 40 years. In case of short temperature excursions, this material will not suffer of any significant overaging. However, this parameter must in all circumstances be maintained below 150 o C. From the activation point of view, the chromium content can be an additional advantage. Due to lack of information, especially threshold propagation data, the mechanical behaviour and loss of some important properties could not be assessed for periods as long as 40 years; among them, resistance to fatigue and in service material toughness, which are RPV life limiting factors. Nevertheless, based on shorter experience, 6061-T6 alloy could be used, provided a proper surveillance programme is carried out, which with this material could be efficiently done, in view of its mechanical characteristics. (author)