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Application of extreme value analysis of radioactivity concentration in environmental matrices and dose to members of public around Madras atomic power station, Kalpakkam

J.Thulasi Brindha, S.Ramkumar, M.R.Balagurunathan, Anitha Manu, A.Thilakavathi, K.R.Sreedevi, V.Santhanakrishnan, T.Jesan, S.Rajaram, A.G.Hegde

Extreme value analysis is a statisticalmethod applied to study the extremes and to forecast the same over a period of time. Generally, statisticians have used this analysis in meteorological data, in construction and design of structures. This paper presents the extreme value analysis of radiological parameters measured in environmental matrices for a period of 20 years in 1.6 to 5 km zone of Kalpakkam. Extreme value analysis is used to quantify activity concentration of Cs-137, Sr-90, I-131,H-3 in sea water,H-3 in fresh water and air moisture and external dose due to Ar-41 during 1989-2008. This study revealed that H-3 concentration in sea water alone followed the Fisher-Tippett Type-I extreme value distribution and in the rest such as Cs- 137, Sr-90, I-131 in seawater, H-3 in freshwater and airmoisture and external dose due to Ar-41 followed Fisher-Tippett Type-II extreme value distribution. Various distribution parameters for each variable were determined using which the activity concentration and total dose to the members of public for return periods of 5, 10, 15, 20, 25 and 50 years were derived. It was observed that based on the extreme values these dose levels were lower than the limits prescribed byAERB.