Estimation Formula of the Variation in Mechanical Strength of Borated Aluminum Alloys

Among the properties, such as thermal, containment, shielding, and criticality properties, which are required for spent-fuel casks for transport and/or storage, it is the thermal and criticality properties that play a very important role for the baskets that hold spent-fuel assemblies. The use of aluminum alloys for baskets offers significant advantages in thermal conduction and light weight. Furthermore, if aluminum alloys that contain boron are used, there is the merit of criticality. Thus, borated aluminum alloys are one of the materials suitable for baskets. In addition, baskets may need to be evaluated for structural strength because baskets must demonstrate safety-related properties in order to hold spent-fuel assemblies. For this reason, it is necessary to design baskets with material strength in mind. The borated aluminum alloy that has been adopted for such baskets at Kobe Steel Ltd. is a precipitation hardening aluminum alloy (6000 series) which contains some boron. In general, it is known that the material strength of precipitation hardening aluminum alloys decreases with overaging. That is, the material strength of 6000 series aluminum alloy decreases with the growth of Mg2Si precipitates. It is therefore necessary to design baskets taking into account the deterioration of material strength caused by overaging during the period of use.