Comparison of distribution of radioiodine observed in brown algae and a diffusion simulation on northeast coastal area of Japan

Since 2006, ¹³¹I (radioiodine) has often been detected in the seaweed 'Eisenia bicyclis (arame)' on the coast of Miyagi Prefecture. In order to ascertain its origin, the authors performed a material diffusion simulation for the sea area around Onagawa. The simulation result is as follows. In order for 0.3 Bq/kg of ¹³¹I to be detected in the sea area in front of the power plant, it is necessary to presume 0.5 L/sec of filtrated water leakage, which is contrary to the fact. In addition, the concentration distribution obtained from the simulation is completely different from the actual detection situation. Therefore, it is inferred that ¹³¹I is not caused by the Onagawa Nuclear Power Station. (A.O.)