API PUBL 7103-ed.1997

Die Annotation des Normtextes API PUBL 7103-ed.1997 :

API PUBL 7103, 1997 Edition, November 1997 - Management and Disposal Alternatives for Naturally Occurring Radioactive Material (NORM) Wastes in Oil Production and Gas Plant Equipment

Natural radioactivity occurring at trace concentrations in oil and gas production streams occasionally accumulates as scale or sludge in tubing and in surface equipment to exceed background levels. Since the radioactivity is generally low and of natural origin, its accumulation and significance were not noted and studied until recently. The American Petroleum Institute (API) has subsequently sponsored studies to characterize accumulations of naturally-occurring radioactivity in oil-field equipment, and to determine safe methods for their disposal. This report presents the analyses of disposal methods for naturally-occurring radioactive materials (NORM) from oil and gas production. It builds on results of a previous safety analysis of disposal methods for NORM wastes in Texas, including a broader range of petroleum industry wastes, more detailed characterization, and covering a broader range of disposai alternatives.

Understanding the radiological safety of NORM waste disposal alternatives is vital to waste management and disposal decisions. Priorities in these decisions are to protect against harmful radiation exposures and to accomplish the disposal in a practical manner proportionate to any hazards posed by the NORM. Since radiation exposures depend on both the quantity of NORM and on its isolation, disposal safety depends on both the waste characteristics and the disposal method.

NORM concentrations vary from background levels to levels exceeding those of some uranium mill tailings, suggesting a similarly broad range of suitable disposal alternatives. Disposal of wastes containing NORM clearly does not require precautions for common cases in which NORM occurs at background levels. When elevated occurrences are found, their disposal should be handled in a way that protects against significant radiation exposure. The disposal problem is compounded by the lack of standards for pertinent alternative disposal methods or for defining the precautions needed for different kinds of NORM. Although detailed regulations provide for disposal of radioactive wastes that clearly pose health risks, there is less guidance on the disposal of wastes containing NORM with elevated radionuclide concentrations. As a result, some wastes containing extremely small amounts of NORM are occasionally sent to elaborate disposal sites at extremely high costs, wasting money, manpower and resources.

This report addresses the problem of what can be done with residues and equipment containing elevated NORM. It systematically identifies the maximum quantities or concentrations of NORM that can utilize various disposal alternatives, implemented at either arid or humid sites. It considers NORM that occurs in sludges from surface equipment, in pipe and tube scales, in cleaned equipment containing residual scales, and on surfaces of gas plant equipment. The waste disposal alternatives analyzed for sludges and scales include landspreading, landspreading with dilution, surface pipe non-retrieval, burial at unrestricted sites, disposal at commercial oil-field waste sites, disposal at licensed NORM disposal sites, disposal at licensed low-level radioactive waste sites, burial in surface mines, placement into wells being plugged and abandoned, injection into inactive wells, hydraulic fracturing into unused formations, and injection into salt domes. Disposal alternatives analyzed for equipment containing NORM residues include release for general use, release for re-use within the petroleum industry, storage in an oil-field equipment yard, release for smelting, and burial with NORM scales and sludges. For each waste disposal alternative, radiation exposures are considered from radon gas inhalation, external gamma-ray exposure, groundwater consumption, surface water consumption, dust inhalation, and food consumption. Using the NORM concentration limits for each disposal alternative, NORM wastes can be reliably managed in the most cost-effective manner while still protecting public radiological safety.

ORIGIN AND NATURE OF NORM

Naturally-occurring radioactive materials are ubiquitous in the environment, and commonly occur in soils, water, food and air. The NORM that accumulates in surface petroleum production equipment is predominantly radium-226 and radium-228 and their progeny, which come from the uranium-238 and thorium-232 decay chains, respectively (Figure 1-1). Both uranium and thorium occur naturally in underground formations and remain mostly in place. However their radium decay products are slightly soluble, and under

some conditions they become mobilized by liquid phases in the formation. When brought to the surface with liquid production streams these nuclides may remain dissolved at dilute levels, or may precipitate because of chemical changes and reduced pressure and temperature as the fluids are separated and processed. Since radium concentrations in the original formations are highly variable, production fluids also are highly variable and occasionally may exhibit elevated radioactivity. Varied formation and surface chemistries cause additional variations in radioactivity brought to the surface. Fluids injected into formations also affect the mobilization of natural radioactivity, and surface processes further vary the accumulation of any radioactivity in scales, sludges, and waste products. Scales and sludges