Radioactive sources, both large and small, are used in many industries throughout the world. Some of these sources fall through the cracks of the radiation programs to which they belong and are misplaced or lost. Because their appearance rarely gives away what they truly are, these sources often find their way into scrap yards. Many steel mills recycle scrap from these yards by melting it down and turning it in to various bar and sheet products. If the steel mill were to melt down one of these sources, the products they make will be contaminated. If the source is large enough or if there are multiple sources, then this could pose a serious health risk to the public.
To reduce the risk of receiving radioactive materials from the scrap vendors, many steel mills have implemented radiation detection equipment at the gates to their property. These detectors are often large area plastic scintillators designed to detect gamma radiation from sources. These systems typically consist of multiple detectors and a control box that is monitored by an operator in the gate house. While these gate monitors are well designed, it is still very difficult to detect a source within a load of scrap. Often, these sources are encapsulated in some form of shielding and to complicate things further, the scrap metal and the sides of the container act as shielding as well.
The gate scrap monitors are the first lines of defense for the steel mills. Many of them have added secondary monitoring on cranes that pick up the scrap to load it into trucks or rail cars that take the scrap into the actual mill. Also, as the interior cranes load scrap into the charge buckets, which are then dumped into the furnace to be melted down, they pass the scrap by another radiation monitoring system. If there are any radiation sources in the steel at this point, this is the last chance that the mill has to find it before it is melted into the steel.
If the mill does melt down a radioactive source, it is important that the radioactive steel is not transferred to other mill equipment, or even worse, formed into product and allowed to leave the site. The later in the process that the radiation in the steel is discovered, the more costly/ time consuming it will be for the steel mill to clean-up. Most mills have implemented testing of the steel after it has been melted down by taking a sample and putting it under another radiation detector. This is done before the molten steel is placed into casting equipment.
One of the biggest problems for a steel mill Radiation Safety Officer (RSO) is the ability to monitor all of these systems. They are usually separate systems made by multiple manufacturers and therefore do not work together. Through training and procedures, the RSO determines what happens in the event that one or more of the radiation monitoring systems were to alarm. Unfortunately, the RSO is sometimes not informed for hours, days, or not at all when they do alarm. Recently, this has been addressed and there is a system out there that can integrate multiple radiation detection systems so that they operate together. Data can be logged and monitored from a single location, such as the RSO’s office. Also, this system can be set up to notify the RSO of an alarm through email or can send a message to their pager. This can be a huge benefit to the RSO. The system is called MillAlert and more info can be found through the link below.