Measurement of 222Rn flux, 222Rn emanation, and 226,228Ra concentration from injection well pipe scale.

Abstract

222Rn flux (Bq s(-1)) was measured from the ends of twenty sections of produced water injection tubing (pipe) containing barite scale contaminated with naturally occurring radioactive material. Exposure measurements near the pipes were as high as 77.4 nC kg(-1)h(-1) (300 microR h(-1)). Flux measurements were accomplished by first purging the pipes with dry nitrogen and then collecting the outflow (nitrogen and radon) on charcoal columns affixed to the end of the pipe for 66 hours. As determined in this manner, 222Rn flux from the ends of the pipe ranged from 0.017 to 0.10 Bq s(-1) (0.46 to 2.7 pCi s(-1)). Following the radon flux measurements, pipe scale was removed and a representative sample was taken for 226Ra and 228Ra concentration measurements and determination of 222Rn emanation fractions (the fraction of the total radon contained in a material that is released from the material and free to migrate). The samples were also analyzed for gross mineral content. Emanation fraction measurements for 222Rn ranged from 0.020 to 0.063, while 226Ra concentrations ranged from 15.7 to 102 Bq g(-1) (424 to 2,760 pCi g(-1)). Barite was the predominate mineral in 17 of the 20 scale samples collected. Much of the previous work dealing with radon emanation fraction measurements has involved uranium mill tailings. Compared to mill tailings and natural soils which have emanation fractions that typically range from 0.1 to 0.3, the emanation fractions measured for these NORM scales are substantially lower.