Carbon-14 (14C) is a particularly interesting radionuclide from the perspective of dose estimation due to the nuclear fuel cycle. The International Atomic Energy Agency (IAEA) programme on Environmental Modelling for RAdiation Safety (EMRAS) includes a tritium (3H) and 14C working group (TCWG), the goal of which is to establish the confidence in the predictions of environmental 3H and 14C models. The TCWG has developed two scenarios regarding 14C called “Rice scenario” and “Potato scenario”, respectively, in which various model predictions were compared with observations. The rice scenario is supported by 10-year monitoring data from 1991 to 2001 collected by Japan Atomic Energy Agency (JAEA) around the Tokai reprocessing plant, which provides a good test of models that predict 14C concentrations in air and rice plants growing very close to a continuous atmospheric source of 14C. The potato scenario is based on the data obtained by a series of experiments on 14CO2 exposure to crops in a wind tunnel, giving a model-data comparison on 14C dynamics in the plant under an acute exposure condition. This report presents some parts of ongoing discussion on the scenarios in the TCWG.
The worldwide environmental protection is required by the public. A long-term environmental assessment from nuclear fuel cycle facilities to the aquatic environment also becomes more important to understand longterm risk of nuclear energy. Evaluation of long-term risk including not only in Japan but also in neighboring countries is considered to be necessary in order to develop sustainable nuclear power industry. The author successfully simulated the distribution of radionuclides in seawater and seabed sediment produced by atmospheric nuclear tests using LAMER (Long-term Assessment ModEl of Radionuclides in the oceans). A part of the LAMER calculated the advection-diffusion-scavenging processes for radionuclides in the oceans and the Japan Sea in cooperate with Oceanic General Circulation Model (OGCM) and was validated. The author is challenging to calculate probabilistic effective dose suggested by ICRP from intake of marine products due to atmospheric nuclear tests using the Monte Carlo method in the other part of LAMER. Depending on the deviation of each parameter, the 95th percentile of the probabilistic effective dose was from one third to two thirds of the 95th percentile of the deterministic effective dose in proforma calculation. It means that probabilistic assessment can contribute to the design and optimisation of a nuclear fuel cycle facility.
Internal exposure to alpha particles emitted from 222Rn (radon) and its daughters is the second leading cause of lung cancer. As a source of indoor radon in home, there are interior building materials that contain radioactive minerals. These radioactive consumer products have been claimed by distributors to have effect of “minus-ion” or “radon spring” for healthy promotion. We analyzed radioactive nuclides contained in the interior building materials, and measured radon levels released from them. The results of gamma-ray spectrometry revealed that these interior building materials contain U- and Th-series nuclides. The densities of some radioactive nuclides in the tile used for a bathroom exceeded the exempt limits of International Basic Safety Standards. However, the radon densities released from the the was lower than detectable limit. In contrast, one of the wallpaper released 34Bq·m-3 of radon gas in a 50-liter container. This value is two times higher than the average radon level in Japanese homes. The “minus-ion effect” wallpapers are thought to be a cause of residential exposure to radon.