Study on radiological aspects in inland mining and refilling by BSM Industry Unit, Chavara

Sand mining is a practice that is used to extract sand from various environments such as beaches, dunes, inland, dredged from ocean and river beds of interface regions. This raw sand along the coasts of India contains large reserves of heavy minerals - ilmenite, rutile, zircon, sillimanite, monazite, etc. The Chavara Unit of IREL (India) Ltd situated in the south west coast of Kerala (8.98210 N & 76.52600 E) is a DAE unit involved in HM beneficiation. Mining of inland area having raw sand rich with HM is also practiced by this unit. The radiologically significant component in BSM mining area is largely Monazite, a Naturally Occurring Radioactive Material (NORM) - the principal ore of Rare Earths and Thorium. It is important to assess the radiological aspects of pre-mining and post mining scenario as the geology is altered due to extraction of NORM materials like monazite, compared to the original land geology. Surface soil samples (03 each) from inland mining areas – both pre-mining and post-mining at refilled and refurbished conditions were collected of five locations and analysed for NORM radioactivity of ²³²Th, ²²⁶Ra & ⁴⁰K. Gamma radiation field was also measured with a calibrated NaI(Tl) based low range survey meter during each sampling. The observations clearly show significant reduction in radioactivity levels and gamma dose rate levels at post/refurbished scenario from pre-mining levels, due to extraction of monazite from raw sand. The activity levels of ²³²Th in the refilled areas were 3% (Karithura-1) to 21% (Karithura-2) of original levels while ²²⁶Ra were 3% (Karithura-1) to 26% (Vellanathuruthu) of original levels. The annual external gamma dose with occupancy factor 0.2 were estimated and found to be 0.75 to 11.10 mSv.y-1 in pre-mining scenario while it is only 0.21 to 0.58 mSv.y-1 in refilled scenario which falls in the world wide average of 0.3-1.0 mSv.y-1[2] and is a significant change in NHBRA