Japan Atomic Energy Agency

ABSTRACT This study aims to reduce waste derived from extractant-impregnated adsorbents by assessing the reusability of spent adsorbents generated during extraction chromatography for the separation of minor actinides (MA(III)) from high-level liquid waste (HLLW). Regeneration was investigated via (i) stripping of the extractant with organic solvents and (ii) re-impregnation of the support. n-dodecane and 1-octanol were examined as candidate solvents. In addition to evaluating stripping performance and the adsorption/elution performance of re-impregnated adsorbents, vacuum distillation was applied to the post-stripping solutions to separate and recover the extractant and solvent. The results demonstrate that the extractant can be stripped from the adsorbent by solvent treatment and that the adsorption and elution performance can be restored by re-impregnation. Furthermore, efficient separation of solvent and extractant from the stripping solution was achieved when n-dodecane was used.

Here we exploited room (298 K) – and cryogenic (77 K) – temperature mechanical behaviors of binary Al-Mg alloys across a wide range of magnesium concentration (i.e. 2.8–13.1 at.%). We observed ductile-to-brittle transition at 77 K as Mg content increases from 7.5 to 13.1 at.%, with a significant reduction from 161 J to 14 J in impact energy. Through detailed theoretical calculations and experimental observation, this composition-dependent transition is discovered to be primarily associated with Mg segregation-induced grain boundary (GB) expansion and charge density depletion at the GB. This finding not only addresses the surging need for durable low-temperature lightweight materials, but also provides an insight in designing superlight aerospace structural materials capable of withstanding the harsh environments encountered for space exploration.

Since the accident at the Fukushima Daiichi Nuclear Power Station in March 2011, numerous studies have examined the behavior of radioactive cesium (¹³⁷Cs) in the ocean. Recent studies suggest that large amounts of particulate ¹³⁷Cs deposited on land are transported to coastal waters via rivers, becoming a major source of coastal ¹³⁷Cs input. Although numerical simulations and conceptual studies indicate that particulate ¹³⁷Cs entering coastal waters can be transported offshore through sedimentation, resuspension, and lateral transport, long-term, high-frequency observational studies remain limited. In this study, we evaluated the transport of particulate ¹³⁷Cs in coastal area off Fukushima using one year of continuous measurement data from multiple moored systems.Moored systems were deployed at three sites near the mouth of the Ukedo River, where current velocity, current direction, and turbidity were continuously measured from February 2017 to February 2018. These data were combined with regularly collected measurements of suspended solid concentrations (mg/L) and particulate ¹³⁷Cs concentrations (Bq/L) to estimate hourly lateral fluxes of particulate ¹³⁷Cs (Bq/h). The study area is influenced by ¹³⁷Cs inputs transported via the Ukedo River, and the relationships between particulate ¹³⁷Cs fluxes and seasonal variability, meteorological conditions (waves, precipitation, and wind), and river discharge were analyzed. Furthermore, by focusing on differences in fluxes among the observation sites, we examined the factors controlling riverine input and transport variability from the coastal area toward offshore.This study uses long-term monitoring data off Fukushima to improve understanding of particulate ¹³⁷Cs transport processes in coastal waters and to provide observational constraints for future numerical modeling studies.

Shifts in precipitation patterns with less frequent rain events accompanied by global warming will trigger soil drying and rewetting, even in humid regions. Because rewetting of dried soil provokes pulse carbon dioxide (CO2) emissions from soils, the chronic soil dry-wet cycle (DWC) in humid regions may provide positive feedback, contributing to global warming. In this study, we aimed to reveal the effects of repeated DWCs on soil CO2 emissions, and the factors affecting emissions after rewetting in humid temperate forests. Experimentation included incubation of soils under five sequential DWCs. CO2 emissions from the soils were measured throughout the incubation period, except during periods of drying. Soil extractable organic carbon (EOC) and microbial biomass carbon (MBC) were also measured at three hours and at five days after the first, third, and fifth rewetting. Rewetting of dried soil significantly increased CO2 emissions during the first DWC, whereas the size of the pulse CO2 emissions after rewetting decreased with an increasing number of subsequent cycles. Soil rewetting decreased soil MBC and increased EOC, and the EOC concentration decreased during each subsequent wet period. Based on path analysis, MBC three hours after rewetting was strongly and positively correlated with CO2 emissions in the following five days in the dry-wet treatment (regression coefficient β = 0.710, p < 0.001). The results suggest that microbial survivability to soil DWCs, rather than sudden labile carbon supply, determines the response of pulse CO2 emissions from soils after rewetting during repeated soil DWCs in humid regions.