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We collected 14 water column seawater samples in the southwestern part of the Sea of Okhotsk and employed low-background γ-spectrometry with convenient minimal radiochemical processing to determine the activities of 226Ra (half-life t1/2 = 1600 y), 228Ra (5.75y), and 137Cs (30.2 y) of the samples. All of these nuclides exhibited unique vertical profiles; 226Ra, 228Ra, and 137Cs activities exhibit small variations from 50–500 m depth (226Ra, ~ 2 mBq l−1; 228Ra, ~0.4 mBq l−1; 137Cs, ~ 1 mBq l−1); These profiles can be explained by convective mixing of surface water to this layer.

A total of 30 surface water samples were collected at 2 sites on the east side of the East China Sea (ECS) during 2008–20f0, and 226Ra, 228Ra, and 228Th activities were measured using low-background γ-spectrometry. The 228Ra/226Ra and 228Th/228Ra activity ratios of the samples exhibited notable seasonal variations (228Ra/226Ra = 0.2–3.3; 228Th/228Ra = < 0.1–0.4) accompanying salinity changes (31.0–34.6). These changes are hypothesized to cause the change by altering the mixing ratio of 228Ra-rich and particle-rich continental shelf water within the ECS.

To understand the pattern of sedimentation rates as fundamental physical parameter of coastal environment, the 210Pb dating method was applied to core samples collected from Kagoshima Bay, Southwestern Japan. The sedimentation rate varied at each location within the bay (0.08–0.30 g·cm−2·y−1), and the rate at the bay-head area was less than that at the centre of the bay. The inventory of ex210Pb has a lower value in the bay-head area. The low ex210Pb inventory at Stn.5' is considered to be due to physical, and chemical conditions in the bay-head area.

The Zr and Mo removal from HLLW is the current issue for repeated usage of the CMPO/SiO2-P-packed column. The adsorbability of the 2-mm-sized HDEHP/SiO2-P adsorbent, which was prepared by fabricating a SiO2 particle from the vibration cutting method and adapting a new polymerization method, was evaluated by the batch-wise adsorption experiment. In spite of the impregnation ratio of the HDEHP extractant, the extraction of Zr and Mo ions from the simulated HLLW was achieved but lanthanide ions e.g., Nd and Gd were also extracted as a minor component. Such unusual adsorption behavior of lanthanide ions could be only provided by accurate, sensitive and reliable micro-PIXE analysis. [ABSTRACT FROM AUTHOR]

In 2014 and 2015, we examined the spatial distribution of cesium-134 (half-life: 2.06 years) from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) in marine sediments within coastal-basin areas (water depths of 40-520 m) off central Honshu Island (the main island of Japan) in the Sea of Japan. The Cs concentrations in both the surface sediment (0-1 cm depth) and whole-core inventory exhibited wide variations, and were highest at the site closest to the Agano River Estuary area (6.7 Bq/kg-dry and 886 Bq/m, respectively). This indicates that Cs in coastal areas was delivered by riverine suspended solids (SS). Given the spatial variation in Cs concentrations, we believe that Cs partially migrated northeastward within ~50 km along Honshu Island (at water depths shallower than ~140 m), and southwestward, including the Sado Basin area. This is predominantly attributable to the transport of SS by bottom currents and unsteady downward delivery onto the steep slopes of the basin. The total amount of Cs in the study area in 2014 was estimated at approximately 0.6 TBq (decay-corrected to March 11, 2011, date of FDNPP accident). [ABSTRACT FROM AUTHOR]

We analyzed a total of 25 seawater samples collected from 2 columns within the Sea of Japan for Ra (half life 1,600 years) and Ra (half life 5.75 years) by employing low-background γ-spectrometry. The Ra activity level in the deep proper water (DPW) (~0.13 mBq/L) was found to be higher than that of deep waters from the Pacific and Atlantic Oceans (<0.1 mBq/L), indicating its continuous delivery to the DPW by active water circulation before complete radioactive decay. Using a steady state box model of Ra and Ra, the turn-over time in the DPW was calculated to be ~80 years. [ABSTRACT FROM AUTHOR]

Lateral and temporal profiles for concentrations of Cs and Cs were examined in marine sediments obtained from coastal and offshore areas on the Sea of Japan-side of central Honshu. In 2013, concentrations declined sharply from an estuarine (30 Bq/kg-dry for Cs) to offshore areas. In the offshore Sado Basin, the concentration of short-lived Cs, which was not detected (<0.3 Bq/kg-dry) in 2010, was 1-15 Bq/kg-dry in 2011-2013. Discharged riverine materials affected by radiocesium derived from the Fukushima Dai-ichi Nuclear Power Plant have been delivered to this offshore basin. [ABSTRACT FROM AUTHOR]