How Detection Can Mean Protection

By David M. Wassum

David M. Wassum is director of risk management at the Institute of Scrap Recycling Industries, Washington, D.C.

You probably are aware of major radiation incidents, such as the Mexican contamination and the multimillion-dollar cleanup of a New York steel mill. In fact, the possible presence of radioactive materials at scrap processing and steelmaking operations is a recurrent threat, one not always publicized but still serious. During the 1980s, more than 30 incidents have occurred in which radioactive materials were received by scrap processors or steel mills. In some cases, multimillion-dollar cleanups were required as a result of the release of radioactive material. In other cases, operations were severely disrupted, even though actual remedial measures were relatively simple.

The continued occurrence of these types of incidents poses a major challenge to everyone involved in the metallic scrap recycling industry. At the very least, the shipment of radiation-contaminated material to a purchaser could jeopardize a business relationship. In extreme cases, the receipt and processing or consumption of radioactive material could severely contaminate a processing facility, steel mill, or foundry, pose risks to employees and the public, and threaten the continued viability of an operation.

To help you protect your employees and facility, following is a description of possible sources of radioactive material that conceivably could enter the metallic scrap stream, and suggested protection measures.

What Is Radiation?

Here are some basic facts, in extremely simplified terms, concerning radioactivity. The characteristics of a specific substance are determined by the combination of protons and neutrons within the atomic nucleus. Although many such combinations are stable indefinitely, several hundred other combinations of protons and neutrons are unstable and constantly are undergoing decay. This decay process is called radioactivity.

Radiation or radioactivity may exist as particles moving at high speeds or as electromagnetic radiation similar to light and heat. Three common types of radiation are alpha particles, beta particles, and gamma or X rays. A fourth type, neutron radiation, can be created as a result of interactions between alpha particles and light metals, as well as in nuclear reactors and other devices.

Radioactivity typically is measured by the rate at which a radioactive atom decays. During this decay process, various types of radiation (for example, alpha, beta, gamma) may be emitted. The potential threat posed by a particular source of radiation is determined by the identity of the radioactive material (cobalt 60, cesium 137), the form in which the material is present (loose pellets, gas, plated material), and the amount of material present (measured in curies). The effects of radioactive material are further determined by the length of exposure, the presence of any shielding material, and the distance between the source and the exposed individual.

Individuals are exposed to radiation at all times, from multiple sources: cosmic rays from outer space, natural radiation in soil and building materials, television, diagnostic X rays, even the human body itself. Depending on location and other factors, a particular individual may receive a dose of from 100 to 600 millirads per year from this "background" radiation.

Current rules regarding occupational exposure to radiation limit the allowable dose to the whole body to five rems per year. However, it has been recommended that the allowable exposure be reduced to three rems per year. For nonoccupational exposures, limits of 2 mrems (millirems) per hour, or 500 mrems per year, are recommended. Exposures up to these levels, even if continuous, are not believed to have adverse effects on humans.

Radioactivity in Scrap Metal

Radioactive material could enter a scrap plant, steel mill, or foundry in many forms and from a variety of sources. Perhaps the most feared scenario is one in which a shielded radioactive source is located within a load of scrap and enters a metallic recycling facility undetected. When the scrap is processed or melted, the shield may be breached, releasing the radioactive material and causing severe contamination.

Radioactive material could be present in virtually any type of metallic scrap. For example, demolition scrap from industrial operations could contain shielded gauges. Such devices typically consist of a small quantity of radioactive material encased in a lead shield, which may in turn be contained within a steel canister. Although material of this nature is required to bear a "radioactive" label, in the course of many years of industrial use the label could be defaced, removed, painted over, or otherwise obliterated. Thus, the absence of a visible label is no assurance that a device does not contain radioactive material.

Shielded devices are not the only potential source of radioactive material. You need to know the other means by which radioactive materials could arrive at your facility and understand the implications of each.

Loose radioactive material conceivably could be present in a scrap shipment. If a radioactive source such as a gauge or diagnostic device should be damaged or partially dismantled prior to arrival at a scrap plant, the radioactive material (possibly in the form of tiny pellets) could be distributed throughout the load or could be concentrated in a specific area.

Scrap metal conceivably could be radioactive because of alloying with radioactive materials. One possible source of such alloys is aerospace material, such as aircraft engines that contain thorium, a naturally radioactive substance. Another source could be steel manufactured in blast furnaces that contain cobalt 60 as a refractory wear indicator. As the refractory wears out, minute amounts of the radioactive cobalt 60 can become alloyed with the steel, making the steel itself slightly radioactive.

Another problem material is naturally occurring radioactive material (NORM), such as radium, which is present in many natural substances. NORM-contaminated scrap may be generated by oil field operations or other industries involved in the extraction of materials from the earth. During extraction and subsequent processing of these materials, NORM may become concentrated in piping, storage vessels, or other material it contacts.

As can be seen by the myriad potential sources of radioactive material, the issue of potential radioactive contamination is a serious one. Because of the severe risks involved, you need preventive measures. Unfortunately, determining appropriate detection and control measures is not a simple matter.

Detection

Significant advances in detection technology have occurred over the past few years, making installation of radiation detectors a feasible option for many recyclers. However, purchasing an appropriate device can be a complicated decision. At best, such a purchase is only one step in the development of a practical control program for dealing with the threat of radioactive materials.

Three basic types of detectors are available for recycling operations: survey meters, ratemeters, and microprocessor-equipped detection devices.

A hand-held survey meter usually is not practical for screening bulk loads of scrap. This type of detector can identify relatively high levels of radiation, but cannot detect a shielded source in a load of scrap. These instruments are most useful in pinpointing a source of radiation and its intensity.

For screening of scrap-bearing vehicles, such as trucks or railcars, a stationary system using scintillation detectors is generally most appropriate. In these systems, the detectors typically are connected to a remote unit that measures the radiation intensity. The remote unit may be either a ratemeter, which functions by counting pulses of radiation energy collected by the detector and comparing the intensity to the background radiation rate, or a microprocessor incorporating a statistical routine to continuously compensate for varying changes in background radiation.

Detectors using ratemeters generally are not effective in detecting a shielded source within a scrap shipment. Unless the source is located within approximately a foot of the vehicle surface, this type of system is unable to locate it.

In an effort to increase sensitivity, some ratemeter-based detectors are shielded to reduce the effects of background radiation. A ratemeter-based system also can be improved by increasing the size of the detector. However, even these enhanced ratemeters probably cannot detect a shielded source hidden in more than a few feet of scrap metal.

For some types of radioactive material (such as loose contamination, a ruptured gauge, NORM), a ratemeter-based system may be entirely adequate to detect the presence of radiation. However, if the intent is to identify intact, shielded sources with a high level of certainty, any type of ratemeter probably is inadequate. A current ratemeter-based system probably is constrained to a detection probability of less than 50 percent for hidden, shielded sources. In addition, these systems have an inherent problem with false alarms.

The sensitivity of a detection system can be much improved by using a microprocessor. For example, to prevent excessive false alarms, a ratemeter-based system must be set to alarm only when it detects radiation at levels as high as twice the background level. In contrast, a microprocessor-based system, incorporating sophisticated statistical techniques, may be set to alarm at levels only about 10 percent above background. Because of this greater sensitivity, microprocessor-based systems can detect shielded sources deeply hidden within a load of scrap.

Even microprocessor-based systems are not foolproof. While the most powerful radioactive sources probably can be detected with near 100-percent certainty, shielded sources containing less intense radioactive materials may not be detected even using state-of-the-art microprocessor technology. For this reason, a detector alone (even if top-of-the-line) is not the only answer for protecting an operation against the threat of radioactive materials.

What Do I Do When the Alarm Goes Off?

A serious potential problem with most detection systems is the lack of detailed information about the type or extent of radiation present. Some systems are designed to simply provide a "go/no go" signal whenever a shipment passes through the detector. If radiation is within expected limits, the alarm does not sound. If radiation exceeds background levels by some predetermined amount, the alarm will go off. When the alarm sounds, the operator knows only that higher-than-background radiation levels are present or that a false alarm has occurred.

A false alarm generally can be ruled out by moving the vehicle back through the detection system a second time; if the alarm again sounds, the incident is most likely not a false alarm. However, the operator still does not know much about the type or source of the radiation. For example, an alarm could indicate any of the following:

• extremely high radiation levels, posing a serious risk to exposed employees;
• low radiation levels distributed throughout the load (suggesting that the shipment is contaminated with NORM);
• low radiation levels, because the source is contained within an intact shield;
• low radiation levels, even though a shielded source has been ruptured, because the radioactive material is shielded by the mass of the scrap metal in the shipment; or
• loose radioactive material, presenting a serious risk of further contamination if the load is disturbed.

In such a situation, the operator has to make immediate decisions based on incomplete information.

Other systems provide a display of "counts per minute" of radiation pulses detected by the system. While these displays provide more information about the intensity of the radiation field, they do not answer most of the operator's questions.

For these reasons, whenever a detection system is used, the operator also should have a survey meter to further evaluate the shipment. The survey meter could be used to identify the area of the shipment in which the radioactive material is located and to provide a measure of the intensity of the radiation. A survey meter should be used only by trained individuals.

Some operators may be tempted to deal with any alarm by sending the suspicious shipment back to its source. Although this approach may seem expedient, it probably is not a prudent response to a potential radiation incident. For example, a driver may refuse to move a truck suspected of containing "hot" material. Even if the driver is willing to move such a load back to its source, it may be unwise to subject the individual to this risk without knowing the extent of the radiation danger. Likewise, if a vehicle identified as "hot" has entered a plant, it is possible that radioactive material has contaminated the premises, possibly posing a threat to employees and their families. Finally, if a "hot" vehicle is sent back onto the highway, management may become liable for any subsequent contamination. At the very least, such a shipment may be in violation of various regulatory requirements concerning shipment of radioactive materials. For all these reasons, a predetermined action plan is needed to deal with radiation incidents.

Need for a Formal Program

Anyone who purchases a detection system should develop a plan for dealing with an alarm situation. The company selling the detection system should provide detailed assistance in developing this program. Depending on management's desires and the technical expertise of plant employees, a procedure may be developed to use a hand-held survey meter in an attempt to evaluate a suspicious shipment and identify the source and intensity of the radiation. Obviously, any such efforts must be undertaken only with the highest degree of caution.

Alternatively, management may decide to call an outside expert, such as a certified health physicist or a state radiation safety officer, any time an alarm sounds.

Because any currently available alarm system is not 100-percent effective, recycling plant employees also must be trained to look for suspicious materials that could be radioactive. For example, employees should be aware of the types of devices used to contain radioactive material, such as gauges and shipping canisters. The U.S. Nuclear Regulatory Commission has prepared a wall chart containing pictures of typical devices. This publication may be useful for in-plant training purposes.

Scrap plant operational procedures should require that any suspicious material be examined before it is processed. For example, sealed containers should be inspected to determine contents. Likewise, any material that cannot readily be handled by a magnet should be investigated. Because of the heavy lead shielding incorporated in a radioactive gauge housing, lifting such a device with a magnet may be difficult, even though the outer casing of the gauge is steel. Thus, if a container apparently made of steel cannot be lifted by a magnet, the identity of the material should be determined before it is handled further.

Through adequate preplanning, employee training, and use of appropriate detection equipment, you can protect your operations against the significant threats posed by radioactive materials.

Radiation Terminology

Roentgen (R):  A measurement of the intensity of radiation in the air. The term is applicable only to gamma or X-ray radiation. This measure also may be expressed in milliroentgens (mR) or microroentgens (uR). Note: 1 R = 1,000 mR = 1,000,000 uR.

Rad (also millirad or microrad): A measure of the amount of radiation energy absorbed by an object or person; a measure of the radiation dose.

Rem (also millirem or microrem): Another measure of radiation dose, based on the biological damage caused by absorbed radiation. Different types of radiation (e.g., alpha, beta, or gamma) have different effects on the body. A measurement in rems reflects these different effects. Millirem = mrem; microrem = urem.

Curie (also millicurie or microcurie): A measure of the activity of a radioactive material, based on the number of disintegrations per second.

NOTE: For gamma radiation (and X-rays) only, the first three measures are roughly equivalent (i.e., 1 R = 1 rad = 1 rem). However, for other types of radiation, the measures are not equivalent.

Selected Radiation Incidents

February 1983--A radioactive source buried in a load of scrap is charged into the furnace of a New York steel mill, resulting in the contamination of the furnace shop, emission control system, and steel product. Cleanup cost: more than $2 million.

January 1984--A medical therapy device containing radioactive cobalt 60 pellets is dismantled at a Mexican scrap plant. Radioactive pellets are strewn throughout the neighborhood; others are subsequently incorporated in steel products.

May 1985--An unknown cesium 137 source melted with a load of scrap metal causes contamination at a California minimill. Contamination is concentrated in baghouse dust and slag. Cleanup cost: more than $1 million.

September 1987--Dross from an aluminum recycling plant sets off a radiation detector at a scrap plant. The dross had been contaminated with radioactive material from an unknown source.