Study of Radiation Risks from Salt Production from Co-Produced water with Oil Production

The present study has determined the radiation risks generated from using oil produced water containing naturally occurring radioactive materials (NORM) to produce sodium chloride by using sunshine evaporation and crystallization process. The results of the study showed that radium (the main nuclide) will be precipitated and concentrated in the evaporation ponds and is not expected to be present in other phases of the project as crystallizers or in the salt as the final product of the production process. The concentration of precipitated radium-226 during evaporation process has been calculated with the assumption of 5000 m³ daily flooding water in the evaporation ponds and the concentration of radium-226 in the water is about 17 Bq L. The expected activity concentration in evaporation ponds sediment was found to be 91 Bq g^-1 which is much higher than the international limit to be non-radioactive hazardous waste (1 Bq g^-1) and the generated annual NORM waste was found to be 3.4x10⁵ kg. RESRARD 7.0 software has been used to assess the radiation dose to operators at the evaporation ponds in the project. The results showed assuming activity concentrations (91 Bq g^-1 first year and 1820 Bq g^-1 after 20 years of operation) at the evaporation ponds, that any member of the evaporation ponds operators will not receive annual doses in excess of the internationally recommended limit of 1 mSv per year. And the major contributor to the dose will be from external radiation. In addition, the internal dose is also predicted using the same parameters and found to be negligible and this due to the fact that most radon with daughters stay in water and most radon emitted to the air is dispersed. Therefore, the radiation risks associated 31 with project activities during normal operation are rather small on the other hand, specialized and classified personnel are required for the removal of precipitated salts at evaporation ponds, which contain high concentrations of radium-226. The external radiation doses received by the operators have been calculated using the Microshield program and the results showed that the doses for workers handling one drum at distance 0 cm and height of 55 (forklift driver) is 0.0014 mSv/hr and the operator will receive 2.8 mSv per year (2000 working hrs.). Finally and according to the computer study, the risks associated with the project is rather small during operation, but the generated waste deposited at the bottom of evaporation ponds and the disposal of such waste should be considered in the cost benefit calculations and the plan of such these projects. (author)