Chlorine-36 deposition at Tsukuba, Japan, after the Fukushima Daiichi Nuclear Power Plant accident

Many radionuclides were released to the environment during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in Japan in March 2011, including 36Cl, and were transported in the atmosphere and deposited over large areas. However, there have been few studies of the 36Cl release from the FDNPP, and the actual amounts released and deposited have not been accurately quantified. Concentrations of 36Cl in rainwater samples collected monthly at Tsukuba, Japan, during the period January 2010 to September 2011, were determined by accelerator mass spectrometry and used to calculate depositions. In March 2011, the monthly deposition of 36Cl was (1.03 +/- 0.02) x 10-4 Bq m- 2, 18 times higher than the average for March in previous years. Monthly 36Cl deposition was correlated with that of 129I (r = 0.7) and 137Cs (r = 0.8) measured in the same rainwater samples from April to August 2011. The total amount of 36Cl released by the FDNPP accident was estimated to be (1.4 +/- 0.2) x 108 Bq based on the 129I/36Cl deposition ratio of March 2011.