RADIOACTIVE MATERIALS COULD POSE PROBLEMS FOR THE GAS INDUSTRY

Peter Gray
Consultant
Bartlesville, Okla.

Louisiana became the first state to regulate naturally occurring radioactive materials (NORM). The regulations became effective on Sept. 20, 1989, with the adoption of the

"Permanent Rule for NORM."

Although most state and federal radiation control statutes are sufficiently broad to cover radioactive contamination, no other regulatory agency has accepted jurisdiction for NORM.

Naturally occurring radionuclides are widespread in the environment. Many geological formations contain uranium, radium, radon, and other radioactive elements together with oil and gas. When oil and gas are produced, traces of these radioactive element also are produced.1-4

Over time, radioactive elements are deposited in scale and sludges, thus contaminating equipment, vessels, and other facilities in the industry.

Even though existing regulations state that a license is required to "receive, possess, use, transfer, own, or acquire radioactive material," with the exception of Louisiana, there is no clear mechanism to obtain a license for NORM contamination in the oil and gas industry.

In varying degrees of severity, NORM contamination may exist at every oil and gas production site and related facilities including pipe handling yards, metal reclamation areas, natural gas and NGL pipelines, gasoline plants, and NGL refineries and terminals.

NORM CONTAMINATION IS:

A potential health hazard to personnel
A problem in waste management (NORM-contaminated sludges and other waste materials including contaminated vessels and equipment may have to be handled as low-level radioactive wastes and disposed of accordingly.)
A possible public relations problem for the industry.

CONTAMINATION TYPES

There are three types of NORM contamination in the oil and gas industry which show elevated radioactive contamination.

SCALE

Radioactive scale contains uranium, thorium, radium, and associated decay products from the production of oil and associated brines contaminated with NORM. The radioactivity in the scale originates principally from radium, which co-precipitates with barium and strontium sulfate.

Other isotopes in the uranium-238 (Fig. 1) and thorium-232 decay series may also be present. Scale may contain radium-226 in concentrations up to 100,000 picocuries (pCi)/gram.

Radioactive flow-restricting scale may be found in downhole tubing, as well as in aboveground processing and transport equipment. Contaminated with NORM may be piping, sludge pits, filters, brine disposal/injection wells, and associated equipment. Also, soils (and equipment) contaminated from well tubing workovers-both at the well site and at remote pipe cleaning yards-may be contaminated with NORM.

FILMS

Radioactive films, coatings, or plating can form from natural gas production gas or processing. Often invisible to the naked eye, these films contain radon and its decay products normally with no radon precursors associated with them.

Due to radon contamination in natural gas, these radioactive films can be found at gas wellheads, in transport piping, headers, treater units, and pumps, and within natural gas processing plants or other light hydrocarbon facilities.

SLUDGES

Radioactive sludges in pipelines, processing plants, NGL storage tanks and delivery facilities, pigging operations, and gas lines and other filter assemblies can be contaminated with radon in the natural gas.

Sludges may be contaminated with several thousand pCi/gram of the long-lived radon decay products, i.e., lead-210, bismuth-210, and polonium-210. These heavy metal decay products may attach to dust particles and aerosols to become part of the sludge.

In gas lines, filter assemblies remove the radon decay products from the gas together with other particulate matter.

Radioactive scale in the oil and gas industry has been reported in the literature. 5 6 With the notable exception of a 1975 report by Gesell,7 NORM contamination of gas facilities by radon and its decay products has not been extensively reported.

The rest of this article will address gas facilities using personal observations from natural gas and NGL facility surveys for NORM contamination made for many companies during the last few years.

CONTAMINATION DISCOVERED

Radon has been known to be a contaminant of natural gas for nearly 100 years.8 it was only in 1971 that radon was found to concentrate in the lighter natural gas liquids during processing and could present a serious health hazard to industry personnel, particularly to maintenance employees.

Some radon undoubtedly was removed with the NGL's prior to 1971. However, the development of deep extraction techniques to remove more ethane from the gas resulted in the extraction of significantly greater concentrations of radon as well.

This problem was discovered when the radon contamination in propylene became sufficiently high to interfere with liquid level sensors detecting slurry levels in a polypropylene plant.

RADON

Radon is a naturally occurring, highly mobile, chemically inert radioactive gas in the uranium-238 decay series. Radon-222 is produced by the radioactive decay of radium-226, the fifth decay product of uranium-238.

Uranium and radium are present in most soils and rocks in widely varied concentrations, and thus radon gas is widely distributed in the earth's crust. Because it is a noble gas, radon is extremely unreactive.

Once formed, radon is free to migrate as a gas, or dissolve in water, without being trapped or removed by chemical reaction. Migrating throughout rocks and soil, radon is produced with natural gas at the wellhead.

As shown in Table 1, radon contamination of natural gas is a worldwide problem with particularly high concentrations or radon reported in the U.S. and Canada.

When radon-contaminated produced gas is processed to remove the NGL'S, much of the radon is removed also. Radon's boiling (or condensing) point is intermediate between the boiling points of ethane and propane.

Upon subsequent processing, radon tends to further accumulate in the propylene distillation stream. The boiling points of radon, the lighter NGL'S, and propylene are shown in Table 2.

As expected, radon tends to be recovered more completely in plants achieving high ethane recovery. The radon is concentrated in the lighter NGL'S, and is relatively easily detected with radiation survey meters.

As long as it is contained and controlled within vessels, equipment, and piping, radon is not generally a health hazard to employees and the public.

Even in the event of a release of radon-contaminated propane, the threat of fire or asphyxiation would far outweigh the hazard of a short-lived radiation exposure.

Although other radon isotopes exist, e.g., radon-220 (thoron) in the decay of thorium-232; the only radon isotope of concern is radon-222. (Radon-220 and other radon isotopes have very short half-lives and will have decayed before the gas is produced at the wellhead.)

Because of radon's 3.8-day half-life, 99% of the radon will decay to its long-lived lead-210 decay product in 25 days.

Storing the natural gas or NGL's for 20-30 days to allow the radon to decay is the only reliable method to remove the radon.

It has been shown that after 30 days' storage, NGL's removed from a salt cavern are essentially free of radioactive contamination.

RADON DECAY PRODUCTS

As shown in Fig. 1, each atom of radon-222 eventually decays to an atom of lead-210 and subsequently to bismuth-210 and polonium-210 before decaying to stable lead-206.

The half-life of lead-210 (a solid metal material) is 22 years. Therefore, the concentrations of radioactive lead, bismuth, and polonium will continue to increase in pipelines, gasoline plants, tank cars, and trucks for over 100 years.

These long-lived radon decay products present a growing problem to the industry, especially to personnel who may be exposed to contaminated surfaces, sludges, and other waste materials.

Contaminated facilities and waste material problems must be recognized and addressed. The presence of the radioactive metals cannot be detected on the outside of contaminated equipment and vessels. The radiations the materials emit are easily absorbed by the walls of the equipment.

If an alpha/beta probe is held closely to contaminated internal surfaces, and if concentrations are sufficiently high, survey meters may detect the presence of NORM. Laboratory analyses are usually required to determine concentrations of the lead, bismuth, and polonium accurately.

These radioactive materials are not a health hazard unless they are ingested or inhaled into the body, e.g., during maintenance on the facility.

If inhaled, the dust and aerosols containing NORM can attach to the lung surfaces where they emit alpha radiation into the tissue of the lung lining.

Studies of uranium miners indicate that extended exposure to these radon decay products pose an increased risk of lung cancer.9 10

NORM IN NGL SYSTEMS

Although entire natural gas and NGL systems may be contaminated with NORM, some facilities will be contaminated to the extent that they present significant decontamination and disposal problems. Gasoline plants and other NGL facilities will be among the most highly contaminated areas in a system.

During processing in a gasoline plant, just 1 ft from a liquids pump the levels of external radiation from radon in propane may be as high as 25 milliroentgens (mR)/hr. Radiation levels up to 6 mR/hr have been detected at outer surfaces of storage tanks containing fresh propane.

Sludges in gasoline plants are often contaminated with several thousand pCi of lead 210/gram.

Vessels and equipment (in NGL service) which may be significantly contaminated with NORM are shown in Table 3.

Although NORM contamination will be general throughout an NGL facility, the contamination will usually be greatest in areas of high turbulence, such as in pumps and valves.

When workers open equipment and vessels, precautions should be taken to prevent contamination. It is recommended that maintenance procedures include the use of respirators, wet grinding, and good hygiene to prevent inhalation of radioactive dust and other materials.

Occasionally, a plant or other facility which has been processing light NGL'S, particularly ethane and propane, is taken out of service and the facility sold or dismantled. Any equipment with internal surface deposits of NORM must receive special consideration when scrapped, sold, transferred, or otherwise disposed of.

In most cases, analyses for lead-210 will be required to verify the extent of contamination and to determine if special handling is required. Particular care must be used to prevent employee exposure to NORM contamination.

There are potential liabilities involved if contaminated equipment, vessels, and other parts of the facility are released or sold for unrestricted use without first being cleaned and tested to be essentially free of NORM contamination according to state and federal regulations.

Much of the material wastes from a facility contaminated with NORM will have to be handled as low-level radioactive waste and disposed of accordingly. Contaminated wastes should be consolidated and separated from noncontaminated waste to keep radioactive waste volumes as low as possible.

Consolidated contaminated wastes should be stored in a controlled area which has a low occupancy. The area should be surveyed with a radiation survey meter, and if required, the area should be posted in accordance with state and federal regulations.

OTHER NORM CONTAMINATION

In addition to vessels and equipment in NGL service, other facilities susceptible to significant contamination include pigging operations, machine shops, and filter assemblies.

Pipeline sludges can contain small radium-226 concentrations together with a few hundred to several thousand pCi/gram of radon decay products. These sludges require the same handling as low-level radioactive wastes.

The pig itself may be contaminated.

This requires handling the pig with gloves and storage in an area with restricted personnel access.

Machine shops present a special NORM situation. For example, pumps in NGL service may be among the most highly contaminated equipment in a plant.

Occasionally, these pumps need to be checked for leaking seals or impeller balance. NORM contamination inside a pump is often chemically bonded to the pump structural metal and cannot be easily removed without scraping and grinding.

Since rebalancing is usually done by grinding until balance is established, the grinding may generate significant quantities of radioactive dust which can contaminate the shop facility."

Even though pipelines and equipment in dry-gas service may only be marginally contaminated, filter assemblies in dry-gas service may be contaminated with very high concentrations of NORM and require special handling to prevent inhalation of the radioactive dust and contamination of the environment.

REGULATIONS

Radon decay produces radioactive materials which contaminate facilities and equipment. Such wastes and facilities should be treated as much as possible like other facilities and equipment covered by the Atomic Energy Act, e.g., soil contamination limits, criteria for facilities and equipment released for unrestricted use, and rules for proper handling and disposal of contaminated materials.

Several state and federal agencies have potential jurisdiction over NORM, but their application to radon and radon decay products is unclear. NORM does not fall under the definition of source, special nuclear, or by-product material as currently defined in the Atomic Energy Act. Therefore, NORM is not subject to the Nuclear Regulatory Commission regulations.

States have laws and regulations governing the use, possession, handling, and disposal of radioactive material, but their application to NORM is still unclear. With the exception of Louisiana, no specific state regulations to control and regulate NORM exist.

Louisiana specifically exempts the wholesale and retail distribution, possession, use, and transportation of natural gas and NGL's from its regulations, The exemption, however, does not apply to contaminated facilities such as pipelines, gasoline plants, and other physical facilities.

As discussed previously, the application of current federal and state laws and regulations for the control of NORM contamination is unclear and complex.

There is a need to constantly monitor regulatory developments as current knowledge of the NORM issues evolve.

Where possible, input should be directed so as to minimize an over-regulation of NORM contamination in the industry.

REFERENCES

Bunce., L.A., and Sattler, F.W., "Radon-22 in Natural Gas," Public Health Service, Farmington, N.M., Radiol. Health Data Report 1966, pp. 441-4.
Tunn, W., "Investigation on the Trace Elements in Gases from German Natural Gas and Petroleum Fields," Compens.-Dtsch. Ges. Mineraloelwiss Kohlechem, Vol. 75-76, 1975, pp. 96-111.
Kolb, W.A., and Wojcik, M., "Enhanced Radioactivity Due to Natural Gas and Gas Production," Radiat., Risk, Prot., Int. Congress, 6th, Vol. 1, 1984, pp. 93-6.
Pierce, A.P., Gott, G.R., and Myton, J,W., "Uranium and Helium in the Panhandle Gas Field, Texas, and Adjacent Areas," USGS Professional Paper 454-6, U.S., Government Printing Office, Washington, D.C., 1964.
Smith, A.L., "Radioactive-Scale Formation," J. of Pet. Tech., June 1987, pp. 697, 706.
Nancollas, G.H., "Oilfield Scale, Physical Chemical Studies of Its Formation and Prevention," Chemistry Department, State University of New York at Buffalo, Buffalo, N.Y., 1984, p. 14214.
Gesell, T.F., "Occupational Radiation Exposures Due to Radon-222 in Natural Gas and Natural Gas Products," Health Physics, Vol. 29(5), 1975, pp. 681-7.
Satterly, J., and McLennan, J.C., "The Radioactivity of Natural Gases of Canada," Trans. Royal Canada, Vol. 12, 1918, p. 153.
Whittmore, A.S., and McMillan, A., "Lung Cancer Mortality Among U.S. Uranium Miners: A Reappraisal," J. Nat. Cancer Inst., Vol. 71, 1983, pp. 489-99.
Sevc J., Kunz, E., and Placek, V., "Lung Cancer in Uranium Miners and Long-Term Exposure to Radon Daughter Products," Health Physics, Vol. 30,1976, pp. 433-7.
Summerlin, Jr., J., and Prichard, H.M., "Radiological Health Implications of Lead-210 and Polonium-210 Accumulations in LPG Refiners," Journal of the American Industrial Hygiene Association, Vol. 46(4), 1985, p. 202-5.