Internal radiation exposure from TENORM for workers conducting cleaning activities on equipment used at geothermal energy plant.

Abstract

Geothermal energy is predicted to be one of the most important renewable energy sources in the near future. In geothermal energy plants, the secondary products such as the scale containing naturally occurring radioactive material (NORM) and adhering to the surface of equipment produce radiation fields. The workers who maintain and clean such equipment are at a risk to be exposed by the technically enhanced NORM (TENORM). To estimate the risks of radiation exposure to the workers, we assessed internal doses resulting from the cleaning activities on 150 heat exchanging boards used at a geothermal energy plant, focusing on 222Rn, 226Ra, 210Pb, 228Ra and 228Th. The experiment was performed with the subjects of workers and office workers as control, supplying prepared foods and drinks. Using the analytical results of 210Pb, 226Ra, 228Ra, and 228Th in the excretions of subjects, committed effect doses were determined. The annual internal dose for the workers with protective clothing due to the cleaning activities on removing scale, assuming the cleaning activities requires 170h (standard monthly working time) a year, was obtained as 26μSv/y and the total dose including 222Rn inhalation dose was calculated as 323 μSv/y. The additional dose for the cleaning workers was less than the dose limit of 20000 μSv/y for radiation workers, even less than for general population (1000 μSv/y) recommended by International Commission on Radiological Protection (ICRP). However, the elevated inhalation dose for workers conducting cleaning activities may present a health hazard to workers if they deal with excessive materials containing TENORM, work for excessive time or are under inappropriate safety measures.