Long-term trends in gamma radiation monitoring at the multi-facility nuclear site, Kalpakkam, South-India

In this work, the analysis of the long-term environmental radiation monitoring data collected within the Department of Atomic Energy site, Kalpakkam using gamma monitors such as GammaTRACERS (GTs) from 2013 to 2018 and Autonomous Gamma Dose Loggers (AGDLs) located in the site boundary at distances from 1.25 to 2.5 km from 2016 to 2018 are presented with respect to dose variation in different locations/wind sectors/seasons. The average background dose rates are in the range of 140–220 nGy/h except at a location (GT2) where a dose rate of 400 ± 20 nGy/h is found. It is observed that the detectors generally measure the normal background doses and at times slightly higher doses (above background) due to exposure to 41Ar plume during normal operations from Madras Atomic Power Stations. The monitors were categorized into four groups: Group 1 to Group 4. Dose rates higher than normal were observed in Group 1 detectors during winter and North-east monsoon seasons and in Group 3 and Group 4 detectors during summer and South-west monsoon seasons and during January to March months in Group 2 detectors. The gamma dose rates during 41Ar plume transit vary in the range of 600–900 nGy/h. The cumulative annual effective doses at the site boundary, analyzed from 2016 to 2018, due to normal operational releases varied from 11 μSv to 114 μSv in different sectors which is significantly lower compared to annual dose limit (1000 μSv) for public.