Methodology development for characterization of NORM originating for oil industry by using LaBr(Ce) scintillator

The presence of NORM (Naturally Occurring Radioactive Materials) has been recognized since early 1930s in petroleum reservoirs, in oil and gas production and in processing facilities. The origin of NORM waste in the oil industry is due to the formation of both sulphate and carbonate precipitates inside tubulars and other production equipment during oil production.

NORM waste is usually very low-level radioactive waste, which may be sometimes exempted from the radiation regulations, although they present an increased radiation dose rate. There is a widespread need for NORM waste to be characterized and treated properly because of their impact to the human health and environment. The successful characterization of NORM waste will significantly reduce their management costs.

The main objective of this PhD thesis is the development of a fast and cost-effective method for segregation and in situ characterization of NORM waste originating from Oil Industry by using a 1.5×1.5 in. scintillation detector LaBr3(Ce).

The last decade LaBr3(Ce) scintillation detectors have become commercially available and are very promising due to their high light yield (> 65000 photons/MeV) that results in a better energy resolution compared to NaI(Tl) detectors (< 3% FWHM at 137Cs), their decay time of 35 ns and their material density (5.29 g/cm3). Also, there is no need for cooling comparing to HPGe detectors. Thus, LaBr3(Ce) detectors could be a suitable choice for in-situ measurements of NORM.

The method development is based on a combination of experimental gamma spectrometry and computational Monte Carlo techniques for laboratory and in situ measurements.

LaBr3(Ce) scintillator was fully characterized in the laboratory environment (FWHM, energy and efficiency calibration) by using reference point sources and multi-nuclide volume sources made of epoxy material of different densities. Simulated and experimentally calculated efficiencies were compared to determine the accurate dimensions of the LaBr3(Ce) detector crystal.

Optimal NORM radionuclides and the corresponding emitting peak energies for the gamma spectrometry measurements were selected from uranium and thorium radioactive series. The activities of other radionuclides in the series, in radioactive equilibrium with the determined ones can be estimated. Also, the radionuclides not possible to be determined by gamma spectrometry or radioactive equilibrium, can be identified and sent for sampling and radiochemical analyses, if needed.

The method is being developed for Drilling the following NORM waste storage packages: (1) Metallic/plastic drum, (2) Plastic Big Bags FIBC – Flexible Intermediate Bulk Container and (3) IBC – Intermediate Bulk Container. The NORM waste characterization material is Oil Based Drilling Mud – OBM, which is a fluid used to drill boreholes into earth and used while drilling oil and natural gas wells and on exploration rigs.

Uncertainty analysis regarding the density inhomogeneities because of the material moisture will be carried out and a sampling procedure to segregate the NORM packages in groups of different origin will be developed.


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