I–6.
This section provides a brief summary of particular practices that use sources of different categories, and a discussion of considerations relating to loss of control that are specific to that practice. The most likely ways for sources in each practice to become orphaned are discussed and examples of actual occurrences are provided. Category 5 sources are not discussed in detail because they are too small to be of significant safety concern. Nevertheless it is important to underline that any material designated as being subject to regulatory control because of its radioactivity needs to be regulated applying a graded approach. For a summary of the main applications as well as the typical radionuclides and range of activities in use, see Table 2 of Appendix I of Ref. [I–1].
I–7.
Sources have been used for other purposes in the past, so historical applications also need to be considered. The following sections list the main uses of various sources, but they are not exhaustive because technology is constantly improving and because there are some applications, such as calibration, where sources of a wide range of activities are used.
Category 1 sources
Radioisotope thermoelectric generators
I–8.
Application. Radioisotope thermoelectric generators (RTGs) are devices that use the decay heat of a radioisotope to produce electricity. The two radionuclides that have been used most frequently are 90Sr (330 –2.5 ×104 TBq) and 238Pu (1 –10 TBq). The power that is typically generated can vary from a few watts to tens of kilowatts, depending on the activity and radioisotope. There are no moving parts in these devices and, since they are designed to operate unattended for tens of years, they are ideal for supplying power to equipment in remote areas. Hence, they have been deployed fairly extensively in the arctic regions and in space. Many of the devices were originally put in position by the military forces of the USA and the former USSR for remote monitoring or for navigation purposes.
I–9.
Possible causes of loss of control. The fact that such devices are deployed in remote regions at facilities that are often unattended means that they are susceptible to people moving them, acquiring them for illegal purposes or dismantling them for the scrap value of their shielding material. In addition, a change in government and/or a loss of records may mean that such sources can become abandoned and forgotten until rediscovered some time later. Space satellites containing RTGs have also reentered the Earth’s atmosphere, causing concern about the spread of the radioactive material. Box I–1 discusses an event in Georgia that illustrates the potential problems of RTGs becoming orphaned.
Box I–1. RTG accident: Georgia, 2001 |
In December 2001, three woodsmen found two heat-emanating ceramic objects near their camp site in the remote Inguri River valley of Georgia. Two of the woodsmen carried the containers on their backs and experienced nausea, vomiting and dizziness within hours of exposure. The third carried the source attached to a wire. At a hospital in Tbilisi, Georgia, the woodsmen were diagnosed with radiation sickness and severe radiation burns, and at least two of the three were in a serious condition. A Georgian team recovered the sources in early 2002 with the assistance of the IAEA. The sources were unshielded, ceramic sources of two Soviet- era RTGs, each containing about 30 000 Ci of 90Sr. Two of the victims were treated in hospitals in Paris and Moscow for many months before recovering from severe radiation burns. |
Commercial irradiators
I–10.
Application. Large scale commercial irradiation facilities are relatively few in number and typically contain very high activity 60Co and 137Cs sources, in the range of 0.2–600 PBq. Applications include the sterilization of medical products (such as sutures and gloves), preservation of foodstuffs and cross-linking of polymers to change their properties. The sources used in the irradiators vary in physical size, some being large, with others being pencil sized, and each facility typically contains many such sources. The sources are installed in dedicated, large, shielded enclosures that employ either a deep pool of water, or massive lead or concrete for shielding of the source when not in use.
I–11.
Possible causes of loss of control. When the source is exposed, the dose rates inside the irradiation enclosure are very high and a lethal dose could be received in a matter of a seconds. Therefore these facilities have many safety features, which are based on the principles of defence in depth, diversity and independence of safety systems [I–2]. However, unless they are well designed and maintained, safety systems can degrade; and, coupled with human error, accidents can happen. There are no documented reports of such sources or irradiators being abandoned or forgotten about. However, there have been instances involving bankruptcy where the appointed ‘receiver’ has made staff redundant and has not known for a period of time the nature of the hazard under his responsibility. If an irradiator were abandoned, there would be a serious threat of a lethal exposure.
I–12.
A more likely scenario would involve the loss of individual sources from the source rack. Typically the source rack consists of a number of source modules, with each of these set in a frame retaining 30–50 source pencils. Each pencil is about 45 cm long and 1 cm in diameter and contains around 150 TBq of 60Co or possibly 137Cs. If irradiation facilities are not maintained, there is the potential for objects to interfere with the movement of the source rack and to distort the module frames, thus allowing a source pencil to fall out. This has occurred on a number of occasions (see Box I–2) [I–3]. It provides the potential for a source pencil to fall into one of the ‘totes’ that transport the product being irradiated out of the facility. Modern irradiators have source shoulders installed to separate the sources from the totes and monitoring systems at the product exit points to detect such a situation. However, these systems need to be maintained to be effective.
Box I–2. Irradiator accident: San Salvador, El Salvador, 1989 |
This accident occurred in an industrial irradiation facility containing 0.66 PBq of 60Co in the form of a source rack of two modules, each containing a number of source pencils. At the time of the accident there was no relevant regulatory or radiation safety infrastructure, since the country had been in a civil war for ten years. The net effect was a degradation of the safety systems and of the operators’ understanding of radiation hazards. In the accident, three people entered an irradiation chamber in order to free the source rack, whose movement to the safety of the water pit had been impeded by distorted product boxes. The problem had not been recognized for two weeks, and during this time damage to the source rack had caused the source pencils to drop out. Most fell into the water pit, but one fell onto the floor of the irradiation chamber. It is pure chance that none fell into one of the product boxes that could have transferred them out of the facility. The installed monitor on the product exit, designed to detect such an event, had long since failed. One of those who entered the chamber later died and another had to have one leg amputated. |
I–13.
Another consideration is that from time to time a number of the source pencils have to be replaced due to radioactive decay. Normally, the suppliers of the sources would undertake this work, and the old sources would be put into specially designed transport containers for return. At this stage, there is the potential for transport problems to cause delays, resulting in the container being put into storage and possibly forgotten about. A scenario similar to that in the Istanbul accident involving a radiotherapy source could then develop (see Box I–5).
Self-shielded irradiators and blood/tissue irradiators
I–14.
Application. There are a number of smaller irradiators described variously as self-shielded irradiators, or blood/tissue irradiators, that are used in hospitals and clinics. Although they are smaller than commercial irradiators, they still contain sources of high activity. In addition to sterilizing blood, tissue and seeds, they are used for gemstone coloration, insect irradiation as part of insect eradication programmes and research into mutation effects on agricultural products. Typically, such irradiators include a sample chamber with interlocked doors and the sources are moved to surround the chamber or the chamber is moved next to the sources. There is no simple way of accessing the sources themselves once they have been installed in the irradiator. In some cases the irradiator, with some minor modifications, is also used as the source shipping container.
I–15.
While most of these irradiators are fixed in a permanent position, there are some devices, such as ‘Gamma Kolos’ irradiators, which were mounted on heavy trucks or on trailers and transported around the former Soviet Union in order to irradiate seeds as they were being planted. Most of these devices have now been removed from their vehicles and are in storage.
I–16.
Possible causes of loss of control. Few of the fixed devices have been involved in orphan source incidents, in part because of their robust nature and design. The major concern would be the abandonment of such devices, perhaps during times of civil unrest or as a result of bankruptcy. Changes in the research focus of institutions have also resulted in these devices being disused and neglected for a long time. There have been concerns with regard to possible security vulnerability of some mobile irradiators.
Teletherapy devices
I–17.
Application. Teletherapy units are commonly found in medical institutions such as hospitals or clinics for use in cancer treatment. In this application a large source, typically 60Co, but possibly 137Cs, of several hundred TBq, is used, external to the body, to irradiate portions of a patient’s body, particularly a tumour. The physical dimensions of such sources are relatively small, and they are generally cylindrical (a few centimetres in diameter by several centimetres long). The source is contained inside a large shielding device.
I–18.
The ‘gamma knife’ (for stereotactic radiosurgery) is a similar device, but it uses a large number of sources (about 200) to provide radiation beams that can be focused on a particular treatment point in the brain while minimizing doses to healthy tissue.
I–19.
The facilities within which such radiotherapy units are located are specifically designed and include thick, shielded walls as well as other protective equipment.
I–20.
Cobalt-60 sources generally comprise a number of solid metallic pellets or discs within a stainless steel source capsule. The hazard is principally from external exposure, unless the sources are subjected to significant mechanical or heat damage, as would be the case in the metal recycling industry. Then, contamination and the potential for internal exposure would result.
I–21.
The radioactive material in 137Cs teletherapy devices is usually in the form of caesium chloride, which has the necessary high specific activity so that the devices can be physically small enough for treatment purposes.
I–22.
Possible causes of loss of control. In normal usage, appropriate controls will ensure minimal risks. However, if these sources are removed from their housings in an unauthorized manner they can deliver a lethal dose in a short period of time. In addition, as the material of the housing may be perceived as being valuable as scrap, loss of control by theft has occurred on several occasions. This has led to melting or other physical destruction of the housing with the subsequent spread of contamination, either directly or through incorporation of the radionuclide into items manufactured from the scrap metal.
I–23.
Given the massive nature of teletherapy units and the fact that they are used in an environment such as a radiotherapy clinic, the staff of which must have knowledge of radiation protection, it is at first sight difficult to envisage these becoming orphan sources. However, there are well documented examples of this happening, leading to fatalities and serious environmental contamination.
I–24.
Once the containment of a caesium chloride source is breached, the high mobility of the material causes a rapid spread of contamination (see Box I–4)
I–25.
Boxes I–3 to I–6 provide examples from accidents in Juarez, Mexico [I–4], Goiânia, Brazil [I–5], Istanbul, Turkey [I–6] and Samut Prakarn, Thailand [I–7]. Some involved 137Cs, others 60Co.
Box I–3. Teletherapy head accident: Goiânia, Brazil, 1989 |
In 1987 in Goiânia, a private medical partnership specializing in radiotherapy broke up acrimoniously. No one took responsibility for a 50 TBq 137Cs teletherapy unit that was left abandoned in the partially demolished building of the former clinic. After two years some local people dismantled the source and its housing and removed it for its scrap metal value. In the process the source was ruptured. The radioactive material was in the form of compacted caesium chloride, which is highly soluble and readily dispersible. For over two weeks the radioactivity was spread over parts of the city by contact contamination and resuspension. Contaminated items (and people) went to other parts of the country. Recognition of the existence of the problem was triggered by an increasing number of health effects. Overall some 249 people were externally contaminated and 129 internally. Twentyone people received doses in excess of 1 Gy and were hospitalized, of which ten needed specialized medical treatment with four of these dying. The decontamination and cleanup of the environment took six months of intensive effort and produced 3500 tonnes of radioactive waste. |
Box I–4. Teletherapy head accident: Juarez, Mexico, 1983 |
In 1977, a 37 GBq 60Co teletherapy unit was bought from a hospital in the USA by a hospital in Juarez, Mexico. It was not imported legally and the authorities were unaware of it. The hospital did not have the resources to use it immediately and it was put into storage in a commercial facility without a clear indication of the hazards. The relevant senior staff left the hospital. In 1983, a junior member of staff who knew of its existence, but had no knowledge of the hazard, removed it to sell as scrap metal. During transport of the source it was ruptured and some small source pellets were scattered along the road. The source was melted in a foundry and was only discovered when, by chance, a lorry carrying contaminated products set off the alarms at the Los Alamos nuclear facility in the USA. Some 75 people received doses between 0.25 and 7.0 Gy, 814 houses with radioactive material in the steel reinforcing bars had to be demolished, several foundries required extensive decontamination and the waste generated amounted to 16 000 m3 of soil and 4500 tonnes of metal. |
Box I–5. Teletherapy head accident: Istanbul, Turkey, 1998 |
In 1993, a licensed operator loaded three spent radiotherapy sources into transport packages for their return to the original supplier in the USA. However, the packages were not sent and were stored in Ankara until 1998. Two were then transported to Istanbul and stored in a general purpose warehouse. After some time the warehouse became full and the packages were moved to empty adjoining premises. After nine months these premises were transferred to new ownership, and the new owners, not knowing the nature of the packages, sold them as scrap metal. The family of the scrap merchants broke open the source container and unwittingly exposed themselves to the unshielded 3.3 TBq 60Co source. Ten people received doses between 1.0 and 3.1 Gy and showed signs of acute radiation syndrome. Fortunately no one died. The second source, 23.5 TBq 60Co, remains unaccounted for, despite an extensive search and monitoring programme. |
Box I–6. Teletherapy head accident: Samut Prakarn, Thailand, 2000 |
A company in Bangkok possessed several teletherapy devices without authorization from the country’s Office of Atomic Energy for Peace. In late 1999, the company relocated the teletherapy heads from a warehouse it had leased to an unsecured storage location. In late January 2000, several individuals obtained access to this location and partially disassembled a teletherapy head containing 15.7 TBq of 60Co. They took the unit to the residence of one of the individuals, where four people attempted to disassemble it further. Although the head displayed a radiation trefoil and warning label, the individuals did not recognize the symbol or understand the language. On 1 February 2000, two of the individuals took the partially disassembled device to a junkyard in Samut Prakarn. While a worker at the junkyard was disassembling the device using an oxyacetylene torch, the source fell out of its housing unobserved. By the middle of February 2000, several of the individuals involved began to feel ill and sought assistance. Physicians recognized the signs and symptoms and alerted the authorities. After some searching through the scrap metal pile, the source was found and recovered. Altogether, ten people received high doses from the source. Three of those people, all workers at the junkyard, died within two months of the accident as a consequence of their exposure. |
I–26.
In a number of cases there have been some common features, which are significant factors in determining national strategies for dealing with orphan or vulnerable sources.
There was long term storage of the sources prior to use, or at the end of their useful life;
The sources tended to end up in the scrap metal industry;
Recognition of the health effects of radiation was the trigger to the discovery of the accident.
Category 2 sources
Industrial gamma radiography
I–27.
Application. Industrial radiography is in widespread use, and has a high hazard potential [I–8]. The construction and maintenance of petrochemical installations, for example, involves the use of portable radiographic sources of up to 7 TBq for testing welds in pipes and tanks. Some years ago 137Cs sources were used and some of these may still exist. Currently, 192Ir or 60Co sources are most often used, but 169Yb, 170Tm or 75Se may also be used.
I–28.
Devices containing industrial radiography sources are generally small in terms of physical size, although they are usually heavy owing to the shielding contained in them. The sources themselves are very small, less than 1 cm in diameter, and only a few centimetres long. They are often attached to specially designed cables for their proper operation. The portability of these devices may make them susceptible to theft or loss.
I–29.
Most remote exposure radiography devices have a general design whereby the source capsule is physically attached to a short flexible cable, often known as the source assembly or ‘source pigtail’. This is coupled, often by means of a spring assisted ball and socket joint, to a flexible drive cable. When not in use, the source is located in the centre of the exposure device. In use, a guide tube is attached to the front of the container and the source is pushed down it to the required position by winding out the drive cable.
I–30.
In heavy industries such as steel foundries or fabrication plants, portable, mobile (on wheels) or fixed radiographic equipment incorporating 192Ir, 60Co or 137Cs may be installed in purpose-built enclosures. Mobile or fixed installations incorporate heavier shielding than portable source housings and are therefore more difficult to steal or remove.
I–31.
Possible causes of loss of control. The housings of radiographic exposure devices and source changers contain several tens of kilograms of shielding material, such as depleted uranium, lead or tungsten, which may be perceived as being valuable. Also relevant is the fact that the portable nature of most equipment allows it to be used almost anywhere. Often such devices are transported to temporary work sites in remote locations or sites with extreme working conditions. Coupled with this there may be limited or non-existent supervision in place and so there is a real potential for entire containers with their sources to be lost or stolen at temporary work sites. Sources are also at risk of being lost while being transported to temporary work sites. They can end up in the metal recycling industry or remain in the public domain. These are similar problems to those of orphan teletherapy sources, and while the activity levels for industrial radiography are lower, they are still sufficient to produce lethal effects. Perhaps the most significant threat comes from loss of the unshielded source.
I–32.
Poor maintenance, incorrect coupling, incompatible devices, obstructions or kinks in the guide tube can all lead to extreme pressures being placed on the various linkages and eventually to the source becoming decoupled from the drive cable. This poses an immediate threat to the radiographer who is required to survey after each exposure to ensure thatthe source has fully returned to the safe, shielded position. Failure to do so has led to serious exposure of the radiographer and others when the source has dropped out of the equipment unnoticed. To members of the public who find such radiography sources, such sources may look like intriguing items and can easily be picked up and carried back to the family home, often with lethal effects, as illustrated in Boxes I–7 [I–8], I–8 and I–9 [I–9]. In many cases, the onset of medical symptoms is unfortunately the first indication that a radioactive source has been found.
Box I–7. Industrial radiography source accident: Morocco, 1984 |
A 1.1 TBq 192Ir source became disconnected from its drive cable. Owing to a lack of appropriate monitoring, it was not noticed and fell out of the guide tube. It looked like an interesting item and was picked up by a member of the public and taken home. It was out of control from March to June and as a result eight people died. |
Box I–8. Industrial radiography source accident: Cairo, Egypt, 2000 |
A farmer picked up a 3 TBq 192Ir source, thinking it was valuable, and took it home. On 6 May 2000, the farmer and his 9 year old son went to their local doctor complaining of skin burns. The doctor prescribed medication for a viral or bacterial infection. The youngest son died on 5 June 2000 and the farmer on 16 June. On 26 June, a blood test was done on other family members who were showing similar symptoms. The blood test showed severe depression of the white blood cell count and radiation exposure was suspected. The source was located and recovered. Other family members were hospitalized. Four men were charged with gross negligence, manslaughter and unintentional injury because they had failed to notify authorities that the source, used to inspect natural gas pipeline welds, had not been recovered after the job. |
Box I–9. Industrial radiography source accident: Yanango, Peru, 1999 |
It is uncertain whether this accident was the result of someone tampering with a security lock. Recognition of a fault condition came when a processed radiography film was blank. The search for the source focused on those who had been in the area. A welder had picked it up and taken it home in his pocket. As a result of the accident he lost a leg and his wife had a minor lesion. |
I–33.
If the premises are abandoned or the equipment is otherwise left unsupervised, vandalism or other interference could lead to the same problems as those identified for teletherapy sources. The sources are still small and can easily be removed from containers.
I–34.
The industrial radiography industry is highly competitive, with many small companies, and consequently a number each year will cease functioning or become bankrupt. Under these circumstances there is an increased risk that sources could simply be abandoned.
I–35.
The large numbers, work environment, activity level and portability/mobility of most industrial radiography sources make them prime targets for theft (Box I–10).
Box I–10. Theft of an industrial radiography source: India |
A shielded container housing a 185 GBq 192Ir radiography source of activity about 0.3 TBq was stolen by labourers of a garbage collection vehicle. The shielded container was sold to a scrap dealer and the source assembly was kept under the driver’s seat. A search operation, supported by a local police investigation, led to the discovery of the source in a cremation ground. The source was traced by a physical search team. |
High/medium dose rate brachytherapy
I-36.
Application. Brachytherapy is a term that is used to describe the interstitial or intra-cavity application of radioactive sources by placing them directly in the tumour (breast, prostate), in moulds (skin, rectum) or in special applicators (vagina, cervix). Brachytherapy applications are of two slightly different varieties. These are generally referred to as high dose rate (HDR) brachytherapy (Category 2) and low dose rate (LDR) brachytherapy (Category 4 or 5). Both applications use sources that may be small physically (less than 1 cm in diameter, only a few centimetres long), and thus are susceptible to being lost or misplaced. HDR sources, and some LDR sources, may be in the form of a long wire attached to a device (a remote afterloading device).
I–37.
Historically, 226Ra was used for brachytherapy. This use of radium brachytherapy sources predates the establishment of regulatory controls in many States. The sources were encapsulated in platinum in either needles or tubes of a few millimetres in width and up to 5 cm in length. However, buildup of radon and helium gases causes pressure inside the encapsulation and it may rupture, resulting in contamination. For this reason, 226Ra was replaced by other radionuclides.
I–38.
Most modern high and medium dose rate brachytherapy is performed with 192Ir, but 60Co and 137Cs are used in places where the replacement sources might be more difficult to obtain routinely. Sources may be manufactured in different sizes and shapes, including as wires or ribbons.
I–39.
The application of these sources may be either manual or by remote control. For reasons of radiation protection, only low activity sources are used manually, with or without afterloading techniques. Afterloading devices may be heavy, owing to the shielding for the sources when not in use, and the device may be on wheels for transport within a facility. The remote afterloading device may also contain electrical and electronic components for its operation. When using these devices, a catheter is first inserted into the body and then the source, attached to a cable, is introduced by remote control. These devices typically use low activity sources of 137Cs and 192Ir or high activity 192Ir (up to 0.4 TBq).
I–40.
Brachytherapy sources are located in hospitals, clinics and similar medical institutions, and such facilities may have a large number of sources. Brachytherapy is less commonly used than teletherapy, but its use is increasing.
I–41.
Possible causes of loss of control. When not in use, brachytherapy sources are normally stored in lead shielded safes or containers, but there have been cases when the sources were improperly kept loaded in applicators in transport carts. Similarly, sources past their useful life have been left in safes or transport containers.
I–42.
Individual manual brachytherapy sources that may become orphan sources are unlikely to be life threatening, but they could give rise to deterministic effects or significant contamination. The overall problem is, however, increased by the potential for such sources to be lost. A major radiotherapy facility could have several hundred brachytherapy sources that are being continually moved and manipulated. There have been many reported instances of brachytherapy sources being discarded in normal waste, and remaining unknowingly in patients who have been released from hospital, or in cadavers. However the nature of this problem was recognized a long time ago and has resulted in many States adopting a requirement for radiation detectors to be installed at exit points from the facilities where brachytherapy sources are used.
I–43.
If the cable of a remote afterloader breaks, the source may become detached. Failure to recognize these problems may pose significant risks, as illustrated in Box I–11 [I–10]. The risks are similar to those for industrial radiography sources.
Box I–11. Loss of an 192Ir HDR brachytherapy source: USA, 1992 |
On 1 December 1992, the United States Nuclear Regulatory Commission was informed by a cancer centre that a 0.14 TBq 192Ir source lost from its HDR remote brachytherapy afterloader had been found when it triggered radiation alarms at a waste incinerator facility in another city. Apparently, the source wire had broken off during treatment of a patient on 16 November 1992, leaving the source in the elderly patient. The patient received a high dose and died on 21 November 1992 as a result. Over 90 other individuals were also exposed. Although there were some weaknesses in the design of the afterloader wire, the breakage went unnoticed for a long time because of weaknesses in the centre’s radiation safety programme, including the failure to survey patients, the afterloader or the treatment room. An almost identical source wire failure occurred with an afterloader on 7 December 1992, but with minimal radiological consequences owing to the fact that the breakage was noticed immediately. |
Calibration facilities
I–44.
Application. There are a large number of radioactive sources that are used for instrument calibration and other calibration purposes. Because they cover a wide range of radionuclides and activities, this practice cannot be assigned to any one category; however, the larger 60Co and 137Cs calibration sources typically fall into Category 2. Other sources could fit Categories 3 and 4, and instrument check sources could be in Category 5.
I–45.
Some calibration sources, especially those of higher activity, are located in specifically designed, shielded and collimated devices within large shielded facilities. Others are just individual sources that might be used for a variety of purposes within research and educational institutions. Radium-226 has been used extensively in the past for calibration purposes, and 226Ra/Be and 238Pu/Be sources are not uncommon in neutron instrument calibration and neutron shielding experiments.
I–46.
Possible causes of loss of control. For large calibration sources within special enclosures, the causes of loss of control are generally the same as those for teletherapy or brachytherapy devices. For individual sources in lead containers (often known as ‘pigs’), the major factors that lead to them becoming orphaned relate to neglect when the source or equipment is no longer necessary, or when the responsible staff member leaves.
Category 3 sources
Fixed industrial gauges
I–47.
Application. In many industries it is necessary to measure the level, thickness, density, moisture content or presence of a material while it is being mined, manufactured or processed. Use of radioactive sources enables measurements to be made without coming into contact with the material itself. Many different radionuclides, of a wide range of source activities, may be used. Depending upon the specific application, industrial gauges may contain relatively small quantities of radioactive material, or may contain sources with activities approaching 1 TBq. Larger activity (about 100 GBq) 137Cs, 60Co and 252Cf sources, which are used as level, conveyor, dredger, blast furnace or spinning pipe gauges, are Category 3 sources, while most other thickness, moisture/density and fill-level gauges are in Category 4.
I–48.
Blast furnaces that are employed in steelmaking often use 60Co sources to gauge the wear of the refractory lining of the bottom hearth. Spinning pipe gauges use 137Cs to measure the wall thickness of pipes as they are passed through the centre of the gauge. While pipe gauges are included in the category of fixed gauges, they can also be mounted on trucks. However, they can be quite heavy (about 100 kg) owing to their lead or tungsten shielding.
I–49.
Possible causes of loss of control. Sources in this group may be placed in locations unsuitable for continuous human presence. Consequently, they may accumulate layers of dirt, grime, grease and oil, which may cover any warning labels that are present. A facility may have a large number of these gauges. Generally, the devices are not large, but they may be located at some distance from the radiation detector, which may have associated electrical or electronic components within its housing. The locations of such devices or sources within a facility may not be recognized, since the devices may be connected to innocuous looking process control equipment. This lack of recognition may result in a loss of control if the facility decides to refurbish a plant or terminate operations (Boxes I–12, I–13).
Box I–12. Source melt accident: Los Barrios, Spain, 1998 |
On 11 June 1998, elevated levels of 137Cs in the air were detected in southern France and northern Italy. On the basis of meteorological data and analysis, it was concluded that this was due to a release somewhere in the south of Spain or northern Africa. Subsequent inquiries and investigations revealed the following sequence of events. On 30 May 1998, an unnoticed 137Cs source was melted in an electric furnace of Acerinox, a stainless steel factory located in Los Barrios, Spain. As a consequence, the vapours went out through the chimney flue, with some fraction caught in the filter system, resulting in contamination of 270 tonnes of dust already collected. On 1–2 June the dust was removed and sent to two different factories several hundred kilometres from Los Barrios as part of routine maintenance. One company received 150 tonnes that was then used in a marshland stabilization process, increasing the mass of contaminated material to 500 tonnes. The first warning of the event was on 2 June from a gate monitor that sounded an alarm on an empty truck returning from delivering the dust. Authorities were notified of the event on 9 June, and on 11 June the aforementioned elevated airborne radioactivity was measured. The radiological consequences of this event were minimal, with six people having slight levels of 137Cs contamination. However, the economic, political and social consequences were major. A rough estimate of costs includes US$20 million for lost production, $3 million for cleanup operations and $3 million for waste storage. Public alarm was also significant, with major media involvement and political pressure being exerted on the Spanish authorities. |
Box I–13. Blast furnace source event: Romania, 2001 |
In August 2000, a commercial company started dismantling two blast furnaces, with the dismantling of one furnace being completed in June 2001. The decommissioning was carried out without regulatory authorization and was stopped in 2001 when on-site inspections by the regulatory body found radiation levels of 0.5 to 400 μSv/h, with a maximum of 4 mSv/h on some debris bricks. It was determined that each furnace contained about three dozen 60Co (with 110mAg) small radioactive sources of activities between about 0.4 and 20 GBq, which had been installed in 1985 for wall thickness control. The consequences of the event were a significant area contaminated with 60Co and a large pile of lining bricks possibly containing more sources. About a dozen workers may have been exposed but did not appear to have measurable radiation injuries. |
I–50.
These devices are usually installed permanently on product machines and generally will be safe while in use. The greatest problem arises at the end of the useful life of the source itself or the plant or equipment where it is installed. There are many examples where sources have been either removed from equipment and placed in storage, or simply left on the equipment in a disused plant.
I–51.
In some instances, sources have remained in this condition for a long time, and, with the passage of time, knowledge of their existence has been lost. In other instances, only short periods of time have been involved, but key staff left the organization and that part of the site was urgently decommissioned or cleared for economic reasons.
Well logging gauges
I–52.
Application. Well logging devices are generally found in areas where exploration for water, coal, oil or natural gas is under way. A combination of neutron and gamma sources is used for the determination of density, porosity and moisture or hydrocarbon content of geological structures. The most usual neutron sources employed are 241Am/Be of up to 800 GBq, but some use has been made of 239Pu/Be and 226Ra/Be. The gamma sources most frequently employed are 50-100 GBq 137Cs. Smaller sources, often of radium, are still being used for reference purposes. The sources are usually contained in long (1–2 m, typically) but thin (<10 cm in diameter) devices, which also contain detectors and various electronic components. The devices are heavy, owing to the robustness necessary for the environments in which they are used.
I–53.
Possible causes of loss of control. The housings in which neutron sources are stored and transported are large and may appear attractive to thieves. The bulk of the shielding will normally be plastic or paraffin wax and may be thrown away as useless by a thief, leading to a potentially hazardous situation. The housings for gamma sources will normally be shielded with depleted uranium or lead, which could be attractive for its scrap value (Box I–14) [I–11].
Box I–14. Theft of well logging sources: Nigeria, 2002 |
In December 2002, two 241Am/Be sources used for well logging were stolen from an oil company truck while it was in transit in the southern Niger Delta region. Such sources are typically of about 0.7 TBq activity. Public announcements, police efforts and increased border vigilance were all instigated in an attempt to find the sources. Health care workers were also warned to keep a look-out for anyone with prolonged nausea or skin burns. Some eight months later the sources were detected in a scrap metal shipment in Europe. |
I–54.
The nature of the work using these sources requires that they be easily removed from their housings to be introduced into a borehole. If they were not subject to adequate control, it would be relatively simple for the source to be removed and left in a hazardous state. The potential for such sources to become orphaned is similar to that for industrial radiography sources. However, the activities and radiation dose rates are generally lower.
I–55.
While they are usually of lower radioactivity than industrial radiography sources, the portability and use of such devices in remote field locations could make them susceptible to loss or theft.
Pacemakers
I–56.
Application. During the 1970s and 1980s heart pacemakers using radioactive material as the energy source (i.e. very small RTGs) were implanted into a number of patients. The most common radionuclide used was 238Pu (with a small amount of 241Am as a source contaminant). One beneficial characteristic of using 238Pu was that it was easy to shield and gave rise to little external dose rate. However, it is also difficult to detect if the source becomes orphaned (Box I–15).
Box I–15. Melting of a pacemaker: United Kingdom, 2000 |
Quality assurance tests conducted in 2000 of steel from a UK foundry identified that about 140 GBq of 238Pu had been melted. It is most likely that this was from a pacemaker. The foundry had sophisticated portal monitors to check incoming scrap metal for gamma emitting nuclides. However, they were incapable of detecting the 238Pu activity. The doses involved were negligible but the cleanup and disposal costs of such an event are several million dollars. |
I–57.
Possible causes of loss of control. It has not always been easy to keep track of patients and there may have been instances of the implanted source being cremated with the cadaver. It is also possible that such a source may be discarded following an autopsy and May end up in recycled metals. The fact that 238Pu sources are easily shielded also means that they are not easily found.
Category 4 sources
Low dose rate brachytherapy sources
I–58.
Application. Much of the general discussion of brachytherapy under Category 2 sources is also applicable here, except that the activities are lower and some different radionuclides are used. In addition to 137Cs and 192Ir, other radionuclides that have been used include 125I, 198Au and 252Cf.
I–59.
Possible causes of loss of control. These are the same as discussed earlier, except that the hazard is clearly lower with the lower activity sources. Category 4 sources are normally too small to cause significant harm from their radioactivity.
Thickness gauges and fill-level gauges
I–60.
Application. Beta or low energy gamma sources are used for measuring paper, plastics and thin, light metals, with higher energy gamma sources being used in situations where steel plate is being manufactured. Industries such as breweries or soft drinks bottling plants will use low activity sources in quality control to ensure that the bottles or cans are being filled properly. Cigarette manufacturers also use sources to ensure that the proper packing density is being maintained.
I–61.
Radionuclides that are typically used in these industries are 85Kr, 90Sr, 241Am, 147Pm and 244Cm as well as 137Cs. Activities range from 0.4 GBq to about 20 GBq.
I–62.
Possible causes of loss of control. These are essentially the same as for other fixed industrial gauges, but because thickness gauges and fill-level gauges typically use less penetrating radiation of lower activity, the potential hazards are smaller.
Portable gauges
I–63.
Application. Portable moisture or density gauges contain the sources, detectors and electronic gear necessary for the measurement undertaken. Moisture is usually measured with a 241Am/Be source of about 2 GBq and density is measured with 137Cs of about 0.4 GBq. The sources are physically small in size, typically a few cm long by a few centimetres in diameter, and may be located either completely within the device or at the end of a rod and handle assembly.
I–64.
Moisture gauges are used in agriculture to ensure optimal watering, while combination gauges or density gauges are often used in road construction to ensure that the appropriate compaction is being used for the foundation materials.
I–65.
Possible causes of loss of control. The fact that such sources are usually transported in locked boxes in vehicles means that they can be stolen as collateral theft if the vehicle itself is stolen. There appears to be some attractiveness of these devices, as evidenced by the number of them that are routinely stolen. In addition, the sources are used in remote road construction sites. This, and their small size, makes them susceptible to loss of control or theft. Sometimes they are damaged by other road construction equipment and may be overlooked.
Bone densitometers
I–66.
Application. As their name implies, these sources are used in devices designed to measure bone density as part of an assessment of osteoporosis. The radionuclides used are 109Cd, 153Gd, 125I and 241Am, ranging from about 1 to 50 GBq. X rays are now widely used in such devices.
I–67.
Possible causes of loss of control. Historically, there have not been any recorded events involving loss of control over sources in bone densitometers.
Static eliminators
I–68.
Application. In many industries the generation of static electricity in manufacturing creates problems leading to the attraction of dust to components or a possible fire hazard. In order to minimize these problems, static eliminators incorporating sources of 241Am and 210Po may be used. These vary in size from hand-held devices of a few centimetres’ dimensions, to fixed installations up to several metres long and a few centimetres wide. Since static eliminators emit alpha particles, the source construction is fragile and will not withstand physical abuse or fire, either of which may result in a spread of contamination.
I–69.
Possible causes of loss of control. Again, there is not a lot of experience with regard to static eliminators becoming orphaned. However, there was one incident in which it appears that a number of sources were deliberately gathered together and buried.
Category 5 sources
I–70.
Application. There are a large number and variety of Category 5 sources that are used in: X ray fluorescence, electron capture devices, Mössbauer spectroscopy, positron emission tomography checking, tritium targets and smoke detectors. In addition, superficial treatment of skin and ophthalmic lesions may be carried out using 90Sr/90Y sources. Nasopharyngeal applicators (90Sr) replaced the ‘Crowe’ radium probe in the 1970s. In addition, permanent implants of radioactive seeds were developed originally using 222Rn and 198Au seeds. Today permanent implants use 125I, 106Ru/Rh and 103Pd.
I–71.
Possible causes of loss of control. Category 5 sources are of such a low hazard that they generally do not need to be considered in a national strategy. However, they still need to be subject to regulatory controls.
Special situations
Legacy sources
I–72.
Application. Legacy sources are those that pre-date effective regulatory requirements and which may not have been disposed of, either at all or in an appropriate manner. The type of legacy sources present will depend upon when regulatory control began to have effect within a State. The majority of legacy sources are likely to be radium (Box I–17), but not exclusively (Box I–16). The following list provides an indication of the types of radium sources and uses of sources in the first half of the 20th century, some of which involved unsealed radioactive material:
Medical applications, including radium brachytherapy;
Radium luminous devices and luminizing facilities;
Industrial radiography using radium;
Patented fake medical devices;
Static eliminators;
Industrial smoke detectors;
Lightning protection systems.
Box I–16. Non-radium legacy orphan source: India |
Not all legacy sources are radium, but rather this depends upon when regulatory control is first established in a State. A manager from a corporation requested advice from the regulatory body regarding a 185 GBq 137Cs source that had been discovered by a member of staff to be in the corporation’s possession. On investigation, it was discovered that the source had been imported by the corporate office in the early 1950s, when regulatory control in India was in its initial stages. Therefore, the source had not been placed under regulatory control. The source was subsequently dealt with appropriately. |
Box I–17. Discovery of radium luminized instrumentation: United Kingdom, 1984 |
In the United Kingdom in 1984, a company specializing in providing spare parts for vintage aircraft and military vehicles came to the attention of the competent authorities. The company’s warehouse contained over 7000 packing crates of spare parts, and in some 2000 of them radium, mostly in the form of luminized items, was detected. In many cases, the varnish covering the luminizing compound had broken down and radium contamination was present. |
I–73.
Possible causes of loss of control. If industrialization of a State and the associated use of radioactive sources started prior to the establishment of an effective regulatory infrastructure, then there are likely to be a significant number of legacy sources that have been orphaned. In this case, the task becomes one of creating the initial national register. Care will be necessary to ensure there is enough coverage of the various sectors, e.g. medical, industrial and academic uses (including nuclear research).
I–74.
Some doctors bought their own radium brachytherapy sources and stored them at home. These could be inherited by other individuals and might only be discovered by chance. These and other radium sources have been found in bank vaults, where they were sometimes stored because of their value at the time ($100 000 per gram in the 1920s). Since early radium seeds were made of thin gold tubing with the radium salt solution inside, some of these found their way into the gold recycling market. In the USA in the 1980s, a few hundred radium contaminated gold items were recovered as part of a special campaign [I–12].
I–75.
In some States, radium luminizing facilities were widespread in the period from the 1930s into the 1960s and 1970s. Many were operated by the military. Storage facilities that maintained large stocks of luminous items, as might be the case for some military facilities or early commercial airplane or clock manufacturers, may also need to be investigated.
Research and academic uses
I–76.
Application. Applications of radioactive sources in teaching and research are extremely varied. Almost any radionuclide of any activity can find a use in some research work, and therefore, such sources can belong to almost any category.
I–77.
Many of the medical and industrial uses described above can be found in universities and research institutes. Some sources are in modified forms to permit a wider range of operating conditions for research purposes. This can often mean a greater reliance on operating procedures rather than engineered safety solutions, and therefore such uses provide more challenges to maintaining the safety and security of sources.
I–78.
The common sources used in much research are however of low activity and/or of short half-life. Tritium (3H) and 14C are frequently used but they have weak beta emissions, thereby causing less serious radiological problems should control be lost. Many such sources are used in electron capture, gas chromatography and Mössbauer spectroscopy devices.
I–79.
Notable exceptions are the use of large (up to 1 PBq) 60Co and 137Cs sources for irradiation or sterilization of materials and plants, and the use of MBq or GBq quantities of 241Am/Be or 137Cs for density and moisture measurement in agricultural research. Although a few irradiation facilities may be of a similar scale to industrial facilities, most devices are of the fixed, self-shielded type that are designed to accept samples into an irradiation chamber that cannot be physically entered.
I–80.
Possible causes of loss of control. Research work is often carried out as part of a student’s thesis or under a specifically funded contract. Equipment, including radiation sources, may have been obtained specifically for a particular project. When the work is completed or the funding runs out, there may be no immediate or further use for the sources, and the person responsible may leave the organization. In many cases the sources are put into storage, but there might not be any clear ‘owner’ within the organization to take responsibility. So the principal problem with research or teaching sources arises when the equipment falls into disuse and knowledgeable staff leave (Box I–18).
Box I–18. Fatal accident possibly due to a source from a research facility: Estonia, 1994 |
A fatal radiation accident in Tammiku, Estonia, in 1994 [I–13] involved a source originally found in scrap metal delivered to a metal recycling facility in Tallin. The source was estimated to be about 7 TBq of 137Cs in an assembly that probably had been part of an irradiator, possibly in a research facility. |
Former military sites and sites of conflict
I–81.
Application. The military uses of radioactive sources are outside the scope of this Safety Guide. However, some understanding of typical military use is beneficial in that sometimes military sites are abandoned or returned to civilian use. Typical examples of military applications have included:
Radioisotope thermoelectric generators (RTGs);
Sources for simulation training for a nuclear weapons attack;
Calibration sources;
Radium and tritium in luminous devices (larger activities than in civil uses).
I–82.
Possible causes of loss of control. Situations may arise from:
The withdrawal of foreign troops from a State;
Major political changes in a State where the military command structure may have been non-functional for a while;
States or regions that have been the scene of military conflicts.
I–83.
Experience has shown that all of these situations could result in sources becoming orphaned and posing a serious threat to the population. Unless source control has been properly addressed at the time, orphan sources can remain in the environment for a long time and in some cases may still be there from old conflicts (Box I–19).
Box I–19. Sources in war affected area: Croatia, 1991–1995 |
|||
Almost half of the Croatian territory was affected by war from July 1991 to September 1995. The collateral damage was significant and a number of sources were affected as shown in the table below. Most of these are Category 5 sources and below. |
|||
Application |
Original number of sources |
Orphan sources |
|
Recovered |
Burnt or lost |
||
Smoke detectors |
8298 |
1710 |
1180 |
Lightning protection systems |
151 |
60 |
0 |
Medical |
17 |
0 |
0 |
Industrial |
103 |
18 |
24 |
The lightning protection systems, being the most unprotected, suffered the greatest damage. Accessible dose rates were up to 3 mSv/h at 1 m from the source. |
|||
Box I–20. Military sources accident: Lilo, Georgia, 1997 |
In 1992, with the break up of the former USSR, the Soviet Army abandoned its facilities in Georgia. One of these was a training camp in Lilo, which was taken over by the Georgian Army. In October 1997, 11 soldiers developed radiation induced skin lesions. A radiation monitoring search of the facility revealed 12 abandoned 137Cs sources ranging from a few MBq to 164 GBq. These had been used by the previous occupants in Civil Defence Training; with the sources being hidden about the site and trainees having to find them. Many were still where they had been hidden. In addition, one 60Co source and 200 small 226Ra sources used on gun sights were also found on the site. Over six years later the soldiers are still receiving treatment for their injuries. |
I–84.
Another consideration from areas of military conflicts is that the collateral damage caused by shells, bombs and other munitions may involve damage to radiation sources themselves or to the buildings in which they are housed. This can result in the abandonment of the facilities or sources, leaving them available for people to loot or scavenge.