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In order to investigate the effect of boron on the precipitation behavior of β phase in Al-Mn-Mg-B alloy used as a material for cask baskets, 1.00 © 104 hours aging treatment was carried out focusing on the temperature history in the cask as in the previous report, and the Timetemperature-precipitation diagram and Supersaturation-diffusion length-precipitation diagram were evaluated using the change tendency of the specific resistance obtained. In the Al-Mn-Mg-B alloy, although grain refinement by AlB2 was confirmed, the effect of boron addition on the precipitation rate of β phase was hardly recognized. That is to say, it was confirmed that the grain boundary and the interface between B compounds and matrix phase hardly contributed as nucleation sites of β phase. In conclusion, it is considered that the reduction of the solid solution Mg content in the Al-Mn-Mg-B alloy does not occur even after 60 years if the Mg content is 1.0 mass% as in the Al-Mn-Mg alloy. [ABSTRACT FROM AUTHOR]

Al-Mn-Mg alloys have been considered as the most suitable basket material of transport and storage casks for spent nuclear fuels. However, the Mg content should be defined with consideration of their prospective heat histories; e.g. exponentially decreasing in temperature from about 200°C to 100°C during the fuel storage up to 60 years. In this research, precipitation behavior of ¢ phase (Al3Mg2) in AlMnMg alloys was analyzed at various temperatures, focusing on the effects of the amount of Mg. Time-temperature-precipitation (TTP) diagrams for these alloys were depicted by a model which had been developed based on classical nucleation theory. The TTP diagrams were further rebuilt to "degree of supersaturation-diffusion length-precipitation (SLP) diagram", where the degree of supersaturation (S) and diffusion length multiplied by cubic root of Mg concentration (L+A) were involved for predicting the starting condition of precipitation. From the SLP diagram, Mg content of 1.0 mass% was found to be able to maintain sufficiently the solid solution strengthening for 60 years. [ABSTRACT FROM AUTHOR]