Distribution of non-exchangeable organically bound tritium activities at the surface soil around Qinshan Nuclear Power Plant

Annual variation of different forms of tritium in the soil around Qinshan Nuclear Power Plant

Tritium deposited in soil forms HTO and OBT. To further understand the changes of HTO and OBT in different years, HTO and OBT in the soil around Qinshan Nuclear Power Base in different sampling years were measured. According to the annual distribution of HTO and OBT in the surface soil, it could be inferred whether there was a long-term release of tritium in the observed year. From the depth distribution of different years, OBT tends to migrate to the deep. From 2015 to 2020, the correlation analysis between OBT and HTO/soil organic matter showed that HTO contributed more to OBT in surface soil at 250-2000 μm and 53-250 μm particle sizes, but this conclusion did not apply to deep soil. However, there was no significant relationship between OBT activity and soil organic matter content.

High Hydrogen Isotope Separation Efficiency: Graphene or Catalyst?

Single-layer graphene has been demonstrated to be a high-efficiency hydrogen isotope sieving membrane in the electrochemical hydrogen pumping system. In this work, we transferred this membrane to proton exchange membrane water electrolysis (PEMWE), which has wide industrial applications. Two membrane electrode assemblies with decorated Pt and ink-coated Pt were investigated. The graphene with the decorated Pt scheme acquired the reported highest proton-to-tritium separation factor of 19.50 in PEMWE. However, rather than graphene, the decorated catalyst was demonstrated to be responsible for this remarkable separation efficiency. Previous studies from Geim's group underestimated the enhanced separation efficiency of decorated Pt over ink-coated Pt, resulting in an exaggerated separation efficiency for graphene. The behavior of proton transfer with hydrogen isotope separation through graphene was interpreted by a serial-parallel circuit model, which suggested that hydrogen isotope separation occurs at defect sites. The limited separation efficiency for graphene was also well understood by a density functional theory (DFT) calculation using an SW 55-77 model and the transition state theory for the kinetic isotope effect. This research provides a thorough understanding of proton transfer with hydrogen isotope separation through graphene.

Tritium distribution in typical plants around tritium laboratory in south-west of China

A low-temperature desorption method was developed to remove the tissue free water tritium (TFWT) in plants, which dramatically reduces the sample-preparation time from several days to only 2-3 h. Two factors, including spatial distribution and seasonal variation, that influence the tritium distribution and the organic bound tritium (OBT)/TFWT ratios in plants were investigated based on three different kinds of subtropical-basin plants located near the decommissioned nuclear facility in south-west of China. Under the same environmental condition, higher tritium concentration was seen in pine needle (PN) compared with flat bamboo-root (FBT) and wild cotton (WC), while these three plants show similar location- and season-dependent trend of tritium distribution. The location-dependent investigation shows that OBT and TFWT concentration are significantly higher in plants growing in the downwind direction of the tritium laboratory than that in plants growing in the upwind and cross direction. In different seasons, the TFWT in plants reached peak in winter and valley in summer, while the OBT increased continuously with the season changing from spring to winter. The ratios of OBT/TFWT were investigated to evaluate the ability of plants to concentrate tritium into organic matter, which were 0.97-2.72 for PN, 0.89-1.64 for FBR, and 0.80-1.62 for WC.

Distribution of tritium concentration in the 0-25 cm surface soil of cultivated and uncultivated soil around the Qinshan nuclear power plant in China

In this study, tritiated water (HTO) and organically bound tritium (OBT) activity concentration at different depth soil layers (0-5 cm, 5-10 cm, 10-15 cm, 15-20 cm, and 20-25 cm) were measured in uncultivated and cultivated soil samples collected in the vicinity of the Qinshan nuclear power plant (QNPP) in July, September, and December 2018. The concentration difference, the spatial and temporal distribution, the seasonal variation, and the OBT/HTO ratios were investigated. The average ratios of HTO concentration between uncultivated and cultivated soil moisture were 1.20 ± 0.24, 1.39 ± 0.46 and 0.95 ± 0.14 in July, September and December, respectively, the corresponding values for OBT were 1.17 ± 0.31, 1.22 ± 0.49 and 1.08 ± 0.28. In generally, the highest HTO concentration in uncultivated soil was found for the topsoil (0-5 cm) in July and September and for the deeper soil layer (20-25 cm) in December, while for cultivated soil, the highest levels were found for the middle layer soil in July, for the topsoil (0-5 cm) in September, and for the deeper layer soil (20-25 cm) in December. Both soils, the vertical profile distribution of OBT concentration showed no consistent tendency, and there were no significant differences in the HTO and OBT concentrations between different soil layers, except for the highest concentration. Whether uncultivated soil or cultivated soil, HTO activity concentrations showed an apparent spatial distribution and seasonal variability, decreasing with the distance to the release sources and with sampling time, while OBT concentrations showed lower spatial and seasonal variability than HTO. In most cases, the OBT/HTO ratios were less than 1, with average values of 1.01 ± 0.48 and 1.06 ± 0.86 for cultivated soil and cultivated soil samples, respectively. The results of this work suggest that farming may affect tritium behavior in soil, while the spatial and temporal distribution of tritium is only slightly impacted.