Carbon-14 transfer into rice plants from a continuous atmospheric source; Observations and model predictions

Koarashi, Jun   ; Davis, P. A.*; Galeriu, D.*; Melintescu, A.*; Saito, Masahiro*; Siclet, F.*; Uchida, Shigeo*

Carbon-14 (C) is one of the most important radionuclides from the perspective of dose estimation due to the nuclear fuel cycle. Ten years of monitoring data on C in airborne emissions, in atmospheric CO and in rice grain collected around the Tokai reprocessing plant (TRP) showed an insignificant radiological effect of the TRP-derived C on the public, but suggested a minor contribution of the TRP-derived C to atmospheric C concentrations, and an influence on C concentrations in rice grain at harvest. This paper also summarizes a modelling exercise (the so-called rice scenario of the IAEA's EMRAS program) in which C concentrations in air and rice predicted with various models were compared with observed concentrations. The modelling results showed that Gaussian plume models with different assumptions predict monthly-averaged C concentrations in air well and also that specific activity and dynamic models were equally good for the prediction of inter-annual changes in C concentrations in rice grain.