Choosing and Using Scrap Radiation Detection Equipment.
Radioactive, or "hot" scrap has been an issue of concern for ferrous foundries for years, and it shows no signs of cooling. The Nuclear Regulatory Commission, Rockville, Maryland, estimates that 2 million scrap sources containing varying levels of radioactive material exist, with only 27,000 of them specifically licensed. In other words, the vast majority of these sources aren't controlled, which means this problem for scrap processors and ferrous foundries isn't going away anytime soon.
In addition to radioactive sources, there's the threat of scrap contaminated by naturally occurring radioactive material.
Beyond the obvious health and safety risks to plant employees, radioactive sources in scrap pose dire risks to the bottom lines of foundries. One contamination can shut down a facility for months or more, contaminate equipment and large portions of the plant, and cost millions to clean up.
Given these potential risks, the obvious question is: What can foundries do to prevent radioactive sources and scrap from entering their facilities?
The answer lies in radiation detection equipment, either at their scrap supplier, their own facility--or both.
When properly installed and operated, such equipment can provide a high degree of protection for your employees and facility, as well as protect your foundry from incurring the exorbitant cost of contamination cleanup.
This article is a review of the types, selection criteria and proper use of radiation detection equipment to ensure that your firm is prepared.
All radiation detection devices sense radiation using either a sodium iodide crystal or a 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 signal the presence of radiation.
One challenge for detectors is to sense background radiation and ignore it because it exists everywhere but varies by amount geographically and changes naturally depending on weather and other atmospheric conditions. A plastic scintillator, for example, senses radiation (including background radiation) and interprets it as light. If the level of radiation exceeds the background level--usually by at least 10%--it will emit more light and sound its alarm.
There are three types of radiation detection equipment: large area stationary systems, handheld detectors and small area stationary detectors.
The large area systems, also referred to as fixed or portal monitors, use plastic scintillator technology and are the most widely recommended for medium-to-large foundries because of their ability to screen material faster and more effectively than smaller units. Plastic detectors also are reportedly more rugged, have a larger area with which to sense radiation and are the most sensitive systems available. They also can withstand wide temperature swings and inclement weather better than sodium iodide units.
Large area portal monitors typically are 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 foundry operation. The most sophisticated portal systems adjust automatically to changing background radiation levels and thus offer the highest ease of use and reliability among detection equipment.
Handheld and small area detectors usually detect radiation with sodium iodide and are less sensitive than large area portal systems. Handheld detection devices, sometimes referred to 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.
A portable radiation monitor may be used as a primary means of radiation screening for facilities that have only the slimmest chance of handling radioactive scrap, such as operations that accept material from one or two exclusive suppliers that produce consistent scrap. Portable detection devices are reportedly time-consuming and labor-intensive to use. For these reasons, they aren't recommended for screening large amounts of scrap coming in by truck or rail because the unit's accuracy and efficiency depend directly on the training, ability and thoroughness of the user. In addition, the slow scanning ability of portable equipment precludes the efficient operation and flow of scrap through all but the smallest foundries.
Portable monitors are widely recommended as supplemental detectors, such as when a portal monitor is the primary form of detection equipment. In addition, some types of portable monitors can detect a source of radiation and identify the type of source. One scrap processor added 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
Radiation detector manufacturers can help you select the equipment that meets the specific monitoring needs of your foundry, taking into consideration the size of your operation, the types of scrap you melt and how most scrap arrives at your facility.
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. Foundry operations, at the minimum, must have a handheld radiation detector, 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.
The detector also should be as convenient as possible to use and cause minimal disruption to your foundry's operation.
A foundry also should keep the following in mind:
Sensitivity--Effective monitoring systems should be sensitive enough to measure the often low levels of radiation emitted from sealed radioactive sources. The system also should be sensitive enough to monitor 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. Manufacturers can help with installation and operation and provide maintenance guidance.
All material and vehicles entering and leaving your facility should be properly monitored. This includes incoming and outgoing scrap as well as waste or byproducts such as ash, dross, slag, flue dust and dirt, and any finished products. Empty vehicles and containers also should be monitored. In addition, foundries may want to monitor scrap one last time before it is charged.
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 operations, this means having at least one detector on each side of the load and perhaps one above the load. However, care must be taken in placing the detectors. Ideally, they should 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 include 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 user noted that his company calibrates its detection equipment every few months as part of its ISO 9000 quality management system. Many of the newer 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 timetable and may identify a problem before you even know it exists.
At least one employee per shift should be trained in the operation of the equipment and the procedures for responding to an alarm. 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. Signs also should be posted informing customers of the procedures your foundry follows in the event that radiation is detected.
Ensuring Your Protection
While radiation detectors are becoming more commonplace in foundries, and manufacturers continually update the sensitivity of the units, most experts note that even the most sophisticated units aren't a panacea. For instance, 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.
So what's the solution?
In addition to having radiation detectors and trained operators, 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 industry are focusing on ways to reduce the chances for such devices to find their way into a foundry 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," cautioned a scrap processor who's been working on this issue for years. Currently, he explained, 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 said, "people would be more careful about tracking the sources and making sure they don't enter the scrap stream at all."
One hope is that new technology will 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 addition, there has been discussion of a new detector material made of silicone rubber and other ingredients that are less fragile than sodium iodide or plastic scintillators, more durable, more flexible and less susceptible to magnetic fields. The material is under development by national laboratories working on a solution to the problems of radioactivity in the scrap industry. Following other recent research, radiation detection equipment makers have successfully installed detectors in grapple.
Until further advances occur, however, the current roster of radiation detection equipment is more than adequate to help protect you, your employees and your entire foundry from the real and potential radioactive sources among us.
John Deere Sleeps Easier With Radiation Detection Equipment
In the late 1980s, the possibility of radioactive material being co-mingled in scrap metal for melting was not a worry for most foundries. At John Deere Foundry (JDF), the concern wasn't even on the radar. Reality set in when reports were, made of a truckload of office furniture setting off radiation detectors at a weigh station in the southern part of the U.S. The reports spelled out the amount of dollars spent in capturing the products produced from this molten metal, the amount of downtime at the plant for cleanup and lost production.
Although no incident regarding radioactive scrap metal had ever occurred at JDF, the risks associated with the problem were too great to ignore. A small group from purchasing, melt process engineering and plant engineering was put together to research available technology for monitoring, possible placement of equipment at the foundry, risk assessment of missed contaminated material and budgeting for the expenditure.
Several months of research resulted in a proposed plan for a detection system that would require all incoming material to pass through to avoid risk of non-detection. A turnkey installation was chosen to avoid any problems with the critical connections between the sensors and the monitoring points.
When installation was completed (30 days), a considerable amount of time was spent with the manufacturer to learn the system. Radiation detection is a sophisticated process that calls for a maximum amount of information gathering without alerting the user. The tuning of the equipment and training of the personnel assigned to its use is a major part of the work of the equipment supplier. Plant personnel, railroad switching crews and security all must be involved with this training and have a good understanding of the entire scope of the project. This will ensure that people have a healthy respect for any items that are legitimately detected as radioactive. Having a detailed written plan for all key employees is a must. It includes whom to contact at JDF, emergency contacts and federal government agencies. It also assures untrained personnel that melt down is not imminent when the alarm sounds.
Our current plan for incoming scrap metal inspection has a mandatory pass through a radiation detection system prior to entry into JDF. The panels used for detection are located in a manner that ensures they travel between them when switched onto John Deere property. The rail crew knows that cars cannot pass through the detectors at more than 3 mph. Should the alarm go off, the crew stops the train and notes the position of the car in question. When the alarm sounds, indicators go off in the meltshop, security and the X-ray laboratory. Melt shop personnel will respond by assessing the situation. The analyst from the X-ray lab also is certified in radioactive material and proceeds to the site with a handheld detection unit. Security continues to monitor the entire situation via handheld radios.
The system JDF uses is finely tuned to remove the majority of background noise that may cause false alarms.
In conjunction with the on-site radiation detection units, JDF changed all of its specifications on scrap metal. Its paperwork now states that any radioactive material shipped would be cause for the termination of the business relationship. JDF also uses scrap yards that have the ability to check their incoming and outgoing scrap metal with detection units. Our regular visits to scrap yards that supply us with these materials include a discussion on this topic and an overview of their capabilities.
This also allows JDF the opportunity to look at new developments in radiation detection technology. Although the basic concept of monitors detecting emissions has not changed, the equipment has. It now appears that the monitors are smaller and lighter, and can be placed in locations the older, heavier ones could not. Some scrap yards are using monitors suspended from overhead cables or beams to look down into trucks and rail cars. Different combinations for spacing give a complete vertical side picture of the load. Computer interfacing makes the job of recording data regarding a particular time or day much easier than a handwritten system.
Even though JDF has never suffered from a "hot" load of scrap, I know we all sleep a little easier because we have one more base covered on a potentially crippling item.
Harvey M. Ulfers, Jr., John Deere Foundry, Waterloo, Iowa
Waupaca Plays it Safe with Radiation Detection Equipment
Radiation detection has been an important issue at Waupaca Foundry for the past 5 years. After hearing of radiation-related incidents at other companies, it was clear to us that between lost production and cleanup costs we could lose millions of dollars. This prompted us, as well as our suppliers, to respond quickly to this potential problem.
When the decision was made to install radiation detectors, we setup interviews with a few manufacturers and then our technical people to evaluate each system. Our people looked for reliability, ease of use and cost to determine which one we would go with.
All of the units that we ordered were packaged to include installation recommendations and onsite training for our people, who would eventually install each unit.
We require all of our scrap suppliers to have radiation detectors in place for all of their incoming and outgoing scrap. In addition, we require that each load show that it has been detected for radiation and signed and dated on the bill of lading. We also check each load with our detectors prior to entering our plants.
There has been little or no change in our overall operations or scrap supply due to radiation detection. Since installation, we've had only a few warnings of radiation, and those only have been background levels due to weather or medical procedures that were currently being done on truck drivers.
The greatest benefit of radiation detectors is knowing that by using these instruments, the potential of receiving radioactive material is nearly non-existent. Although radiation detectors are relatively expensive, we at Waupaca feel it's a small price to pay in comparison to having an incident on site.
Tony Lewis, Waupaca Foundry, Waupaca, Wisconsin
Responding to an Alarm
Before you have a radioactive "event" at your foundry, 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 vehicle with the portable unit. In some instances, 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 in. 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;
* Survey the inside of the vehicle, including welds and dirt. If any materials are detected with high radiation levels, isolate the material and contact the state radiation control office.
|Printer friendly Cite/link Email Feedback|
|Comment:||Choosing and Using Scrap Radiation Detection Equipment.|
|Date:||Nov 1, 1999|
|Next Article:||Variables that Affect Cope Oxide Inclusions in Steel Castings.|