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Radioactive materials in scrap metal

In recent years, the amount of radioactive material finding its way into scrap yards and steel mills has increased significantly, leading to a rise in the demand for the installation of radiation detection equipment at metal recycling facilities. While the origen of such uncontrolled (orphan) radioactive sources entering the recycled scrap metal stream is very often unknown, a large contribution to radioactive contamination is thought to come from scrap metal imported from former Soviet Union countries. Often there is no obligation under law for the seller to state the origen of the metal; in any case, loads often become mixed thus making origin identification difficult, and cases have been reported where radioactive warning signs are covered with adhesive tape. Some of these sources have gone undetected, and been accidentally melted down or shredded and thus entered the metal stream. Furthermore, finished metal products have recently surfaced in Russia in which scrap metal from the Chernobyl area had been used in fabrication; these products may later enter the recycling process in through normal channels.

Currently there is no international protocol for the detection of and response to radioactive materials in the scrap metals stream, and procedures are often put in place on an ad hoc basis. A notable exception is Spain in which protocols for reporting and disposal of radioactive materials in scrap metal have been in place since 1999. However, the United Nations Economic Commission for Europe (UNECE) has recommended the establishment of a voluntary international Protocol providing for a consistent and internationally harmonized approach to monitoring and response procedures (April 2004).

While radiation detection systems, particularly portal monitors, have long been standard installations in mills consuming scrap metals, detection equipment is increasingly being placed in scrap yards to detect gamma-emitting radioactive materials in loads brought into the yards. Various types of radiation detectors are used, and as a general rule, the higher the sensitity of the radiaton detector, the higher the probablity of detection of radioative material. It is therefore essential to use high senstivity detectors specifically designed for search and location of radioactive materials.

Radiation detection equipment for scrap recycling facilities

Recent advances in radiation detection technology, driven by the need to monitor and intercept illicit trafficking in radioactive materials at border crossings, have brought to the market a new generation of lightweight, compact and highly sensitive detection equipment, inherently suitable for deployment in scrap metal recycling facilities. Radrisk Consulting will advise you on devices most appropriate for your operation.

Radiation detection instrumentation is require to fulfil several different functions in the interception of radioactive materials passing through the scrap metal recycling chain. Some devices are multifunctional and can perform a variety of tasks, while others are useful for specific tasks only. It is therefore important to have an appreciation of instrument capabilites before committing to purchase. Instruments fall into several catregories, listed below. Further details on the following types of instrument can be found on our radiation detectors page.

Portable gamma monitors - These "search" instruments have developed significantly in the last few years, largely due to the need for efficient search and detection instruments at border controls. There are two main types of portable gamma monitor - Handheld and Pager instrumentrs (see below). Portable gamma monitors are used to scan loads manually for radioactivity, search for radioactive sources within a load once an alarm from a fixed system had signalled the presence of a radioactive source, and also, increasingly, used by workers to make random checks by continuously monitoring radiation levels as they move around the premises. In this last category, Pager instruments are particularly useful , since they are specifically designed to be worn on a belt or pocket. In search mode, portable monitors display the radiation level in counts per minute (cpm), and give audible signals (beeps or chirps) in proportion to the level of radiation. In this way, as the detector moves closer to the radiation source, the counts reading and the audible signal rate increase, allowing the source to be located. Instruments used for search and location of radioactive materials within scrap should be highly sensitive in order to search efficiently, given that the radioactive sources may be shielded by surrounding metal; modern search instruments are based on scintillation (solid state) detectors to give greater detection efficiency than older Geiger-Müller counters. Radrisk offers 3 portable gamma monitors suitable for this application, the PM1710 Handheld gamma monitor, and the PM1703M and NukeAlert 951 Gamma pagers. All are highly sensitive scintillation (CsI) detectors. While the functions of pager and handheld instruments are largely interchangable, your choice between pager and handheld monitors will depend on the following:

  • If you require a handheld instrument to actively scan loads, i.e. the worker monitors a scrap load with the radiation detector in hand, the PM1710 is the radiation detector for you.
  • If you require an instrument for passive monitoring of material i.e. the instrument is worn by the worker and measures radiation levels continuously while the worker performs other tasks, Pager instruments (PM1703M, NukeAlert951) are more appropriate.

Fixed and Portal monitors - Portal monitors are large, fixed monitors usually placed at the yard entrance to monitor incoming lorry/truck loads, often most conveniently located either side of the weighbridge. The metal load is automatically monitored for an increase in radiation levels without operator intervention, with alarms activated when radiation rises above background levels. As with other types of radiation monitors, portal monitors have undergone significant improvements in recent years to address the demands of monitoring border crossings. Generally, the most appropriate system for monitoring trucks entering metal recycling facilities is our PM5000-01 system consisting of a two-pillar gamma radiation monitor, normally installed at the weighbridge. Our PM5000 portal monitors are a modular system allowing configurations from smaller gamma sensors for conveyer monitoring to larger truck monitors, including optional neutron detection capability. We can also configure single-sided fixed monitors with the PM5000 system. Fixed monitors can be attached to walls, pillars or other structures to passively monitor scrap as is passes through the procressing facility, sounding an alarm if preset radiation threshold levels are exceeded. In larger facilities, more sophisicated fixed systems can send signals to a central monitoring station.

Spectroscopic Instruments (Identifiers) - Portable spectrometers, often referred to as Identifiers, are sophisticated instruments allowing for the identification of radioactive substances from their unique gamma radiation signature. The instruments collect and analyse the spectrum of gamma radiation energies emitted by the radioactive substance, display the spectrum on an LCD, and automatically identify the substance from device's inbuilt isotope library. The PM1401K Identifier is the most compact and lightweight portable Identifier in the world, originally designed for border control work, and is a multifunction instrument containing 3 seperate detector units. In addition to identifying radioative materials, the PM1401K Identifer is also able operate in search mode, and in doserate mode; i.e. it can also perform the functions of the electronic dosimeters and search instruments. The instrument also incorporates a neutron detector for enhanced detection of nuclear materials like plutonium. An iPAQ handheld computer, together with data collection and analysis software, is an optional extra with this model. The PM1401K communicates with the iPAQ via wireless Bluetooth or Infa-red connections to send data in real time, allowing the user to monitor data collection and isotope identification from a safe distance from the radioactive source.

Electronic dosimeters - Dosimeters are instruments used to measure the radiation doses received by individuals, and also to monitor the radiation levels, in a workplace for example. They express radiation levels in terms of dose rate (internation units are microseivert per hour µSv/hr). Generally, the response time of dosimeters is too slow to be of practical use as Search instruments. Electronic dosimeters can be used to determine whether levels of radiation emitted by a source are above recommended levels for exposure, although modern gamma pagers and Identifiers (see below) should be able to perform this function.

Types of radioactive material found in scrap metal

Radioactive sources surfacing in the metal recylcling chain originally come from a wide variety of sources, and as we produce, use, and dispose of more and more equipment employing radioactive isotopes, the amount of radioactive material entering scrap metal facilities is set to increase. An important source is material originating from civil nuclear installations, also industrial and research irradiation facilities, producing material contaminated with fission products such as Co-60 and Cs-137, and neutron activated material such as Ni-58. As decommisioning of nuclear power reactors and obsolete military hardware including nuclear-powered submarines gathers pace, scrap from these sources will become increasingly common. Other sources are medical and industrial equipment, principally radiotherapy units using a variety of sources such as Co-60, Cs-137, Ra-226 and Ir-192, portable and fixed humidity gauges employing Am-241/Be neutron emitting sources, anti-static devices using Po-210,, well logging equipment using Am-241, Cs-137 and Cf-252, pipe flow meters using Cs-137, industrial densitometers using Cs-137 , thickness gauges using gamma emitting nuclides Co-60 and Cs-137 or the beta emitting nuclide Sr-90, light sources containing Ra-226, smoke detectors containing Am-241, and various equipment contaminated with K-40 from chemical industries. Additional sources are irradiation units from various applications, miltary hardware contaminated with depleted uranium, mining equipment contaminated with uranium and thorium, etc. These sources will generally be detected via detection of the emitted gamma radiation, although lower energy gamma radiation emitted by isotopes like Am-241 is strongly absorbed in the surrounding metal - thus the use of sensitive equipment is imperative for optimal interception of all source types.

 

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