Studies on Organically Bound Tritium (OBT) and Tissue Free Water Tritium (TFWT) in vegetation around Kalpakkam

Tritium, a pure beta emitter, may get released as Tritiated water (HTO) through 100 metre high stack during the operation of PHWR type reactor. Being released as HTO, tritium follows the water cycle and incorporates partly into biota. A study around Kalpakkam site was carried out to estimate the levels of Tissue Free Water Tritium (TFWT) and Organically Bound Tritium (OBT) in some vegetable and tree leaf samples. TFWT varied from ≤ 3 - 145 mBq/ml and OBT ranged from ≤ 4 - 67 Bq/kg dry. The Specific Activity Ratio (SAR) of OBT/TFWT ranged from 0.2 to 39. At background location both OBT and TFWT were below the detection limit. Wide variation in TFWT and OBT observed in biota can be attributed to the variability in release rates of tritium from the plant and change in meteorological conditions. SAR value above unity can be attributed to the longer retention period of OBT in plants as compared to TFWT. (author)