Radiocarbon variations since 1960 in tree rings around the nuclear facilities of the eastern Japan

Matsunaka, Tetsuya*; Sasa, Kimikazu*; Takahashi, Tsutomu*; Hosoya, Seiji*; Matsumura, Masumi*; Sueki, Keisuke*; Satou, Yukihiko   

To evaluate the radiological impact of the atmospheric C discharge from the Tokai nuclear facilities, a 80-year-old Japanese pine tree from Tokai, 1.8 km south-southwest of the Tokai Nuclear Power Plants (Tokai NPP and Tokai-2 NPP) and 1.4 km North-Northwest of the Tokai Reprocessing Plant (Tokai RP), was cored and each annual ring was measured for C. The C specific activities varied from 232.8 Bq kg C to 403.3Bq kg C in the tree rings formed during the periods 1954-2013. The specific activities in 1967-2010 are significantly elevated compared with the ambient background values, clearly indicating C discharges from the nuclear facilities during their normal operation. The excess C activities of 0.5-70.0 Bq kg C in 1970-2011 are positively correlated with the estimated annual C discharges of 0.1-1.2 TBq from Tokai NPP and Tokai-2 NPP with R of 0.66 (n = 38). These activity values of 70.0 Bq kg C were corresponding to an additional annual effective dose of 3.9 uSv via the food ingestion pathway in the study location.