Macroscopic Evidence for the Hibernating Behavior of Materials Stock

Hibernating stock is defined as material stock that is no longer used, but is not yet recovered. Although hibernating stock plays a role in materials recoverability, its contribution to the overall material cycle is not clearly understood. Therefore, an analysis of the time-series potential generation of steel scrap in Japan was performed and compared against the actual recovery, proving that the steel scrap recovered each year exceeds the annual generation potential and providing the first macroscopic evidence of hibernating stock recovery. These results indicate that hibernation behavior should be considered when evaluating materials recoverability. The particular characteristics of hibernating stock were also identified. These materials tend to be located far from scrap yards and/or have low bulk density, while also minimally obstructing new activity. In fact, hibernating materials are typically only recovered when they obstruct new activity. Hence, in order to increase steel recoverability, the recovery cost must be reduced. The end-of-life recycling rates (EoL-RRs) were also evaluated, and were found to exhibit a significant change over time. Consequently, the annual EoL-RR cannot be considered as a representative value, and a value for the EoL-RR(s) of relevant year(s) that has been evaluated over the entire period should be used instead.