API Bull E2-2006 pdf download.Bulletin on Management of Naturally Occurring Radioactive Materials (NORM) in Oil and Gas Production.
Correlations can be developed to relate gamma or exposure rate measurements to concentrations of NORM in scale or sludge. The operator should exercise caution when using relationships of this type because of the many variables that can affect the rela- tionship. Some of these variables include NORM density, volume, thickness, nuclide composition, and detector efficiency. Facil- ity and equipment-specific correlations will yield better results than generic correlations. Generally, this will require the laboratory analysis of a number of samples collected from equipment reading at different exposure rates to develop a reliable cor- relation. In a similar fashion a correlation for solid waste could be generated by collecting a number of measurements from sam- ples of known concentrations in a repeatable geometry such as a 1 liter open mouth plastic jar. Typically the accuracy of these correlations is on the order of plus or minus 50%. 3.1.3 Direct Measurements Measurements for total and removable alpha and beta activity are performed on surfaces of equipment. For direct measurements, an appropriate detector is coupled to a ratemeter-scaler. A Geiger-Mueller (GM) tube is usually used for beta measurements, and a zinc sulfide scintillator is usually used for alpha measurements. However, many types of detectors are currently available. The surveyor places the detector in contact with the surface at the location where the measurement is desired and counts are accumu- lated for a predetermined length of time, typically 1 minute. The resulting value is in cpm. Conversion factors that correct for detector efficiency, count time, and geometry are applied to convert cpm to more useful units such as disintegration per 100 cm 2 (dpm/100 cm 2 )or Bq per 100 cm 2 (Bq/100 cm 2 ). Measurements to determine removable activity levels are collected by applying moderate pressure to a piece of filter paper or smear paper and wiping the surface over an area of approximately 100 cm 2 .
3.1.4 Radionuclide Concentration In Media In some instances it may be necessary to determine concentrations of NORM in media such as air, soil, scale, and water. Collec- tion techniques vary and require specialized equipment. Analytical laboratories or environmental professionals can provide addi- tional information and describe appropriate sampling techniques. Upon collection, care should be taken to maintain a documented history of the sample. This is referred to as maintaining chain of custody. Samples are sent to radioanalytical laboratories for determination of radionuclide concentration. Soil sampling is the most common form of media sampling at NORM-impacted sites. Reasons for soil sampling may include determining the concentration of radionuclides before the land is released for unrestricted use, or before the sale or purchase of the lease, and characterizing the existing surface activity. Additional soil samples should be collected from a non-NORM impacted area of the site to document the existing soil background levels. It is also possible to make rough estimates for radionuclide con- centrations based on external measurements if enough field correlation data exists for the given site. As a general rule these esti- mates would be used to make follow up analysis decisions when addressing a NORM impacted site and would not be a sufficient basis to plan a remediation effort unless the correlations were specifically developed for a particular area.”
3.1.6 Personnel Internal Radiation Dose Assessment Ambient airborne NORM concentrations are normally evaluated by filtering a high-volume air sample and having the filter ana- lyzed by a radiometric laboratory. NORM deposits in equipment and piping do not present any airborne exposure concerns during normal operations. During maintenance or dismantling activities, airborne NORM exposure concerns are minimized by the appli- cation of typical industrial hygiene practices such as keeping NORM deposits wet and using respiratory protective equipment. On the other hand, during grinding, cutting, chipping and sanding, and during removal of NORM scale, airborne activity may occur. Under such conditions, it is advisable to evaluate employee exposure to ambient airborne concentrations of NORM. Personnel exposures are evaluated by the same sampling and laboratory methodology except that personnel wear lapel air sam- plers that operate at 2 to 5 liters per minute versus the higher flow rate ambient air pumps. In both techniques, it is essential to know the volume of air sampled along with the radiometric results in order to calculate the airborne NORM concentrations.