Development of Aluminum Extruded Alloy for Basket of Transport/Storage Casks (2) Properties and allowable stress of the borated aluminum alloy 1B-A3J04-O -

Basket material of transport and storage cask is required to have enough structural strength under transport and storage conditions to maintain safety functions such as sub-criticality and heat removal. The material is also preferable to be light to reduce the weight of the package because it is very important to improve the efficiency of transport and storage of fuel assemblies. Aluminum is the suitable material for a basket due to its low density and excellent thermal conductivity. However the basket material has the possibility to be reduced its strength due to heat history under storage operation up to 60 years, therefore it is very important to evaluate its strength after 60 years with the proper methods in order to design the basket of transport cask after storage.2. Properties and allowable stress of the borated aluminum alloy 1B-A3J04-OKobe Steel, Ltd. has developed the borated alumimun alloys such as rolled material “1%B-A6061-T651” and extruded material “1%B-A3004N-H112”. The borated aliminum alloy newly developed this time is modified material based on the 1%B-A3004N-H112 to maintain its strength without almost reducing it during operated period.This material is the Al-Mn-Mg alloy added about 1% enriched boron and has the two main strengthened functions i.e. the solid solution strengthened by Mg and the dispersion-strengthened by Mn’s compounds. The strengthening mechanism and the design of chemical composition of this new material are described in detail in the paper of PATRAM 2019 “Development of Aluminum Extruded Alloy for Basket of Transport/Storage Casks (1) – Strengthening mechanism after long term storage and design of chemical composition - ” .As the transport cask will be operated after long-term storage up to 60 years, the degradation during the storage should be considered for the basket design. Therefore, the strengths of this material after 60 years storage have been conservatively evaluated with the accelerated test. As the results, it is confirmed that the evaluated mechanical strengths are almost same as those of the initial condition. The accelerated test results and the evaluated allowable stresses are discussed in the paper.