July/August 1998
Radioactive sources and scrap are out there. Fortunately, so are radiation detectors. This guide looks at such equipment, including how to select and use it to protect your employees and operations.
By Eileen Zagone
Eileen Zagone is an associate editor for Scrap.
They are among us.
No, we’re not talking about the latest “X-Files” episode featuring aliens from another planet, but something even scarier to scrap processors: radioactive sources that could find their way into the scrap stream.
The issue of radioactive, or hot, scrap has been a hot one for years, and it shows no signs of cooling. The Nuclear Regulatory Commission (Rockville, Md.) estimates that 2 million sources—containing varying levels of radioactive material—are “out there,” with only 27,000 of them specifically licensed. In other words, the vast majority of these devices aren’t controlled, which means “this problem for scrap processors isn’t going away anytime soon,” says one scrap executive.
In addition to radioactive devices, there’s also the threat of scrap contaminated by naturally occurring radioactive material, or NORM.
Beyond the obvious health and safety risks, radioactive sources and scrap pose dire risks to the bottom lines of both scrap processors and consumers. A single contamination can have far-reaching effects and can shut down a facility for months, contaminate equipment and large portions of the plant, and cost millions to clean up. According to one industry expert, the cost of cleaning up one contamination at a large steel mill can range from $50 million to $100 million or more.
Given these potential risks, the obvious question is: What can scrap processors and consumers do to prevent radioactive sources and scrap from entering and endangering their facilities?
The answer lies in radiation detection equipment.
When properly installed and operated, such equipment can provide a high degree of protection to your employees and facility. It could also give your company a competitive edge. Says one Midwestern scrap processor: “It gives us one up on the competition.” As he explains, many of his company’s consumers request, but don’t require, their scrap suppliers to use radiation detection equipment, though they demand scrap that’s radiation-free. “They may start requiring it in the future,” he says, “so we’re prepared no matter what.”
To ensure that your firm is equally prepared—no matter what—here’s a review of the types, selection criteria, and proper use of radiation detection equipment.
Detector Options
All radiation detection devices sense radiation using either a sodium iodide crystal or the more sensitive plastic scintillator. When an “ionization event” occurs—that is, when the detector senses gamma radiation—it sounds an alarm.
In sodium iodide units, radiation interacts with a gas in the detector to create an electronic pulse. Plastic scintillators, in contrast, are made of a plastic to which fluor is added so that the material has the ability to emit light—or scintillate—when hit by radiation. These scintillations are then read and amplified into electrical signals that indicate the presence of radiation.
One challenge for detectors is to sense background radiation—there’s background radiation everywhere that varies geographically and changes naturally depending on weather and other atmospheric conditions—yet only sound an alarm when radiation is above the background level. A plastic scintillator, for example, senses radiation including background radiation which it interprets as light. If the level of radiation exceeds the background level—usually by at least 10 percent—it will emit more light and sound an alarm.
There are basically three types of radiation detection equipment: hand-held detectors, small area stationary detectors, and large area stationary systems.
The large area systems—also referred to as fixed or portal monitors—use plastic scintillator technology and are generally the most widely recommended for medium to large scrap processing operations because of their ability to screen material faster and more effectively than smaller units. Reportedly, plastic detectors are the most sensitive systems available with the added bonus of being more rugged and having a larger area with which to sense radiation. They can also withstand wide temperature swings and inclement weather better than sodium iodide units.
Large area portal monitors are typically installed at the scale to monitor incoming and outgoing scrap and vehicles and can usually do so without disrupting the efficient flow of material through a scrap recycling facility. The most sophisticated portal systems adjust automatically to changing background radiation levels and thus offer the greatest ease of use and reliability among detection equipment.
Hand-held and small area detectors usually detect radiation with sodium iodide and are generally less sensitive than large area portal systems. Hand-held detection devices—sometimes referred to colloquially as Geiger counters—are appropriate for analyzing small amounts of scrap at close range, while small area units can be mounted to analyze small trucks and containers, though neither is sufficient to detect radiation in a large truckload of scrap. These types of detectors are less expensive than portal monitor systems and usually have multiple sensitivity settings that can be manually adjusted to changing background radiation levels.
Some scrap processing facilities may also be able to use a portable radiation monitor as a primary means of radiation screening. Such units, however, are only recommended for facilities that have only the slimmest chance of handling radioactive scrap, such as those accepting material from one or two exclusive suppliers that produce consistent scrap, says an industry expert. Portable detection devices are reportedly time-consuming and labor-intensive to use. For these reasons, they generally aren’t recommended for screening large amounts of scrap coming in by truck or rail because the unit’s accuracy and efficiency depends directly on the training, ability, and thoroughness of the user. In addition, the slow scanning abilities of portable equipment would preclude the efficient operation and flow of scrap through all but the smallest scrap processing facilities.
That said, portable monitors are widely recommended as supplemental detectors, such as when a portal monitor is the main detection equipment. Plus, some types of portable monitors can not only detect a source of radiation, but specifically identify the type of source.
One scrap processor adds that his company, which has portal detectors at several plants, uses portable detectors to check all empty railcars that come into its facilities before filling them with scrap for shipment to a consumer.
Selecting the Right One
So, what kind of detector—or detectors—should your company be using?
Radiation detector manufacturers (see “Picking a Detector” on this page) can help you select the equipment that meets the specific monitoring needs of your plant, taking into consideration the size of your operation, the types of scrap you process, and how most scrap arrives at your plant.
In general, choose the strongest, most sensitive detector you can afford, say detection experts, because it will more than pay for itself if it ever detects a radioactive source. Small scrap processing operations should at least have a hand-held radiation detector, experts recommend, while medium to large plants that have many different types of vehicles cross their scale should invest in a large, state-of-the-art plastic scintillator detection system. Shredding operations would also be wise to have a detector on the exit conveyor to check for radiation in the final product, suggest detection professionals. In this instance, the density of the scrap is low enough that a less-expensive sodium iodide system is sufficient.
The detector should also be as convenient as possible to use and cause minimal disruption to your plant’s operation, experts note.
You should also keep the following in mind when choosing a system:
Sensitivity. Effective monitoring systems should be sensitive enough to measure the often low levels of radiation emitted from sealed radioactive sources. The system should also be sensitive enough to monitor effectively through the density of scrap in an average load.
Alarm Threshold Setting. This is the point at which the detector senses radiation that sets off its alarm. The threshold should be set according to the unit’s sensitivity and the background radiation. To reduce the potential for false alarms, detectors that can continuously monitor the background radiation level and adjust their alarm threshold level are the most effective because they can be set at the lowest possible detection limit while still maintaining a low false alarm rate.
Monitoring Time. Radiation detection equipment should monitor, process the received data, and sound an alarm quickly enough that its use won’t significantly slow your workflow. Fixed monitors should be designed and installed with forethought given to the typical material flow of the facility. If the detection system tends to slow the workflow, employees may be tempted to find ways to speed up the process, such as having trucks pass through the detector too quickly. This could be disastrous, as insufficient monitoring time can reduce a unit’s ability to detect radiation. Some systems require trucks to travel less than 5 mph through the portal. For maximum protection, post signs that note the proper speed for passing through the detector and insist that customers follow it.
Proper Installation and Use
Getting the most from your radiation detector means installing and using it properly. Again, detector manufacturers can help with installation, operational, and maintenance guidance.
All material and vehicles entering and leaving your facility should be properly monitored. This includes incoming and outgoing scrap, waste or byproducts such as shredder residue, ash, dross, slag, flue dust, and dirt, as well as any finished products. Empty vehicles and containers should also be monitored. In addition, facilities that melt significant quantities of scrap may want to monitor scrap one last time before it’s charged into the furnace, suggest detection experts.
When positioning a large area portal unit, take into consideration the detector’s sensitivity, the shielding effect of scrap material, containers, or vehicles, and the reduction of detectable radioactivity due to distance and movement of the load. For best monitoring results, detectors should be shielded to minimize the amount of radiation they detect from areas other than the primary detection area.
Portal monitors should be positioned to provide optimal scanning opportunity on an average load, taking into consideration the height of the load and its density. For most scrap operations, this means having at least one detector on each side of the load and perhaps one above. Care must be taken in placing the detectors, however. They should ideally be installed as close as possible to the load being analyzed, but far enough so they won’t be damaged. Also, make sure you know if your equipment can effectively scan moving loads or if it requires loads to be stopped.
Maintenance of detection equipment should cover a daily check to ensure the unit is functioning properly. This includes checking it electronically using battery charge or other tests that are part of the equipment and with a commercially available radioactive check source.
In addition, the detector should be calibrated at least once a year, though one scrap processor notes that his company calibrates its detection equipment every few months as part of its ISO 9000 quality management system. Many of the newer sophisticated radiation detection systems can be diagnostically checked in the field via a modem connection with the manufacturer’s headquarters. These checks can be performed automatically on a particular timetable and may identify a problem before you even know it exists.
At least one employee on each shift should be trained in the operation of the equipment and the procedures for responding to an alarm, suggest detection experts. In addition, written alarm procedures should be posted and discussed with all employees and should include telephone numbers for your state’s radiation control office, the regional office of the Nuclear Regulatory Commission, and the local or state police. (For more details, see “Responding to an Alarm” on page 50.)
Signs should also be posted informing customers of the procedures your company follows in the event that radiation is detected.
Ensuring Your Protection
While radiation detectors are becoming more commonplace in scrap recycling facilities and manufacturers continually increase the sensitivity of the units, most experts note that even the most sophisticated detectors aren’t a panacea. “No matter how expensive the system and how well-designed for your site, no system is 100-percent reliable,” says one scrap processor. “They do have limitations.” For instance, he notes, detectors only check for gamma radiation and can’t always detect sealed sources. Also, the denser the load of scrap, the lower the units’ ability to effectively pick up radiation. “Density affects sensitivity, and very dense material can thwart the ability of the equipment to detect radiation,” he says, adding, “I think some people have become overconfident in the abilities of the equipment.”
So what’s the solution?
In addition to having radiation detectors, make sure employees are trained in how to use the equipment and how to check that it’s working properly, experts suggest. It’s also important to train your work force to be on the lookout for suspicious materials and radioactive symbols on items. Show them what typical potential sources look like and teach them to recognize other clues of possible radioactivity. And make sure they know the proper procedures to follow if a source is detected.
But with an estimated 2 million radioactive sources out there, many in the industry are focusing on ways to reduce the chances for such devices to find their way into a scrap operation in the first place. “More and more radioactive scrap is finding its way into the recycling stream and without stricter government controls, this situation is unlikely to change,” cautions a scrap processor who’s been working on this issue for years.
Currently, he explains, the penalties for losing a radioactive source are so low that it has created a disincentive for the owners to properly dispose of the material. “If the fines were stiffer,” he says, “people would be more careful about tracking the sources and making sure they don’t enter the scrap stream at all.”
Until that ideal is achieved, however, it’s important to note, says Mike Mattia, ISRI’s director of risk management, that strides in communication and cooperation have been made between government, the Nuclear Regulatory Commission, and the scrap recycling industry. Mattia and other scrap industry members are optimistic that this atmosphere of cooperation will continue.
Plus, new technology could always improve the reliability of radiation detection equipment. Some experts also believe that improvements in software are likely in the future, given the significant software advances in the past few years that have reduced false alarm rates and increased sensitivity.
In other positive news, there has been some discussion of a new detector material made of silicone rubber and other ingredients that’s less fragile than sodium iodide or plastic scintillators, as well as more durable and flexible than the current units. The material is under development by national laboratories working on a solution to the problems of radioactivity in the scrap industry. At a recent meeting among the interested parties, a scrap industry member suggested that the researchers look into whether this technology could even be installed in a magnet or grapple.
Until these advances occur, however, the current roster of radiation detection equipment is more than adequate to help protect you, your employees, and your entire company from the real and potential radioactive sources among us.
Responding to an Alarm
Before you have a radioactive “event” at your plant, be prepared with a plan of action to deal with the situation. Experts recommend these general guidelines in devising your response procedure:
Remove the vehicle or container that set off the alarm from the monitoring zone, reset the monitor, then scan the vehicle or container again. If the alarm goes off again, isolate the load. Using a portable survey meter, detect the ambient background radiation level away from the load and also scan the driver and the vehicle with the portable unit. In some instances, scrap processors say, detectors have picked up radioactive pharmaceuticals in the bodies of drivers undergoing medical treatment.
Slowly scan the exterior of the vehicle, making sure the detection surface is no more than 2 inches from the surface, and mark on a diagram of the vehicle where the unit registers levels of radiation above background levels. If the portable detector’s meter registers its highest setting at any time during the scan or if a radioactive device is discovered, discontinue the survey and contact the appropriate state radiation control office.
In other cases, continue examining the vehicle and then individual scrap items in the vehicle, starting with material closest to the exterior areas where radiation levels were detected. Also survey the inside of the vehicle, including welds and dirt. If any materials are detected with high radiation levels, isolate them and contact the state radiation control office.
Picking a dector
The following companies manufacture radiation detection equipment for the scrap processing industry:
Bicron N.E. (Solon, Ohio), 440/248-7400
Eberline Instruments (Santa Fe, N.M.), 505/471-3232
Exploranium (Rio Rancho, N.M.), 505/896-6776
Ludlum Measurements Inc. (Sweetwater, Texas), 915/235-4947
Rad/Comm Systems Corp. (Brampton, Ontario), 905/846-9677
Ronan Engineering (Florence, Ky.), 606/342-8500
Quantrad Sensor Inc. (Santa Clara, Calif.), 408/727-7827
Xetex (Sunnyvale, Calif.), 408/745-6654 •
Radioactive sources and scrap are out there. Fortunately, so are radiation detectors. This guide looks at such equipment, including how to select and use it to protect your employees and operations.