Investigation for Adaptation of Tritium Analysis in Fish Samples Using a New Combustion System

抄録

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident resulted in a large amount of contamination, and decommissioning was required to remove the damaged reactors and decontaminate the surrounding areas has been underway. The contaminated water in FDNPP is treated by the Advanced Liquid Processing System (ALPS), but tritium in the water cannot be removed by the system. The Japanese government then decided to release that water into the ocean, which was carried out by Tokyo Electric Power Company in August 2023. Therefore, it is crucial to understand the environmental impact of tritium and its behavior, as there are concerns about internal exposure to tritium and harmful rumors. To study the effects of tritium on the environment, it is important to determine the concentration of tritium in environmental samples. However, organically bound tritium (OBT) which is bound to the carbon skeleton of organic materials analysis requires several pre-treatments and time. In particular, the combustion process is difficult due to sudden ignition depending on the samples. The recovery of combustion water therefore requires skilled techniques. For this reason, data on OBT in environmental samples is limited. In this study, a semi-automatic combustion system was developed to enable the combustion of water easily, safely, and with reproducibility in the combustion process. Combustion tests were carried out on four different fish samples. To achieve combustion without ignition, combustion conditions were investigated by adjusting the temperature increase program and gas flow rate. In addition, the validity of this method was then verified by evaluating the volume of combustion water recovered. Furthermore, to verify the validity of this method, an analysis was performed on a standard fish sample, and a comparative test was performed with other analytical methods. The results of this test confirmed that the four types of fish were able to complete the combustion operation without sudden ignition. Combustion water recovery rates exceeded 80%. However, sudden ignition was often observed in black rockfish and trout. Therefore, it was possible to prevent sudden ignition by adjusting the sample volume and gas flow rate. Comparative tests of fish standard samples showed similar values of 2.01 ± 0.54 Bq/L for this method and 2.11 ± 0.17, 1.72 ± 0.09 Bq/L for the mass spectrometer method. Therefore, it was confirmed that this combustion device is effective for the analysis of OBT. The method is expected to make obtaining OBT data easier and safer, as well as contribute to a better understanding of tritium environmental impact and behavior.