ISSUES IN THE MANAGEMENT OF ORPHAN SOURCES
6. DETECTION OF ORPHAN SOURCES
Detection of orphan sources is a challenge. They can be found in unexpected locations, and therefore a monitoring system requires the use of different instruments in combination. The major instruments used in detection of orphan sources can be grouped as: (i) pocket sized instruments to alert and protect the radiation protection expert (high sensitivity is required for these instruments); (ii) handheld/mobile instruments to locate, identify and measure the dose rate of the source; (iii) fixed installed (‘portal’) systems to provide automated alarm at installed strategic points.
Since flows of goods, vehicles and people are concentrated at border crossing points, ports of entry (airports, seaports) and highway/railway check-points, regulatory authorities must install and use these monitoring instruments at these nodal points. In addition, scrap metal facility gates, strategic points of transport (e.g. the Bosporus bridges in Istanbul), and other similar points must also be equipped with such monitoring systems.
Installing monitoring systems at these nodal points to detect orphan and illicit trafficking radiation sources is not simple. Coordination is needed between border guards, police, customs officers and radiation protection experts. Protocols should be prepared that define the roles of the various authorities, such as the ministry of industry, the ministry of energy, the interior ministry, the nuclear regulatory authority and other organizations that are responsible for orphan source detection.
A formal agreement between regulatory authorities is necessary for:
(i) strengthening measures to detect, interdict and respond to incidents;
(ii) enhancing cooperation among governmental agencies, especially in the fields of information sharing, communications and training; (iii) pooling resources among competent authorities for the sharing of monitoring and detection equipment.
The content of the protocol should include: field of application; under-takings arising from the implementation of the protocol; actions in the event of the detection of an orphan source; apportionment of costs; detection procedures; and training and joint demonstration exercises. Spain provides a good example of such a protocol. After the Acerinox accident, a protocol entitled Collaboration on the Radiation Monitoring of Metal Materials was signed between the Ministry of Industry and the Ministry of Energy, the Ministry of Development, the Nuclear Safety Council and others.
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7. IAEA MINIMUM PERFORMANCE RECOMMENDATIONS
FOR MONITORING SYSTEMS
A fixed installed monitoring system is the main tool in the detection of orphan sources, and in the process of their selection, IAEA recommendations should be considered [30]. The main selection parameters for a fixed installed monitoring system are: (i) Sensitivity to gamma radiation. It is recommended that at a mean indication of 0.2 µSv/h, an alarm should be triggered when the dose rate is increased by 0.1 µSv/h for a period of 1 s. (ii) Search region. The volume in which efficiency of detection is maintained will vary according to the instrument. Table 1 summarizes the search region in which the performance characteristics for the given alarm levels should be applicable. (iii) False alarm rate. The false alarm rate during operation should be less than one per day for background dose rates of up to 0.2 µSv/h [30].
8. HANDLING ORPHAN SOURCES
Handling orphan sources requires expertise. Trained personnel and proper safety, isolation and notification procedures are the key elements for response to orphan source incidents.
A radiation protection officer (trained personnel) should take personal precautionary measures to prevent a second incident. When an orphan source is found, care should be taken to minimize external and internal radiation exposure. Before an orphan source is approached, a dose rate meter should be available and checked in its most sensitive range. Measurements should be started at least 10 m away from the source, and when the dose rate exceeds 0.1 mSv/h, additional precautions should be taken [30]. The first stage in the process of handling of an orphan source, as mentioned above, is isolation, identification and notification. A durable label should be installed on the
TABLE 1. PARAMETERS OF THE SEARCH REGION Vertical
(m)
Horizontala
(m) Speed
Pedestrian monitor 0–1.8 0–1.5 <1.2 m/s
Car monitor 0–2 <4 <8 km/h
Truck and bus monitor 0.7–4 3–6 <8 km/h
* Parallel to the direction of movement.
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shielding of the source that identifies the important characteristics of the source. The second stage is that of temporary storage. The purpose of temporary storage is to provide safety, security and radiological protection temporarily. Once a suitable route has been identified for transport to interim storage, which is the third stage, it will be necessary to arrange the transport.
Experience has shown that most accidents occur while sources are in temporary storage; therefore efforts should be made to transfer the sources at the temporary storage to an interim storage facility as soon as possible. When a source is received at a central facility, some level of treatment and conditioning may be required before it can be placed into interim storage [21].
9. CONCLUSION
In recent years, the number of incidents with orphan sources has been constantly increasing, with sources being found not only at customs border controls but also frequently in scrap and in other unexpected locations, thereby giving rise to growing social concern in view of the risks involved. For this reason, regulatory authorities and other competent authorities should increase monitoring and update their strategic orphan source search plans to:
(i) establish or strengthen national systems of control for ensuring the safety and security of radiation sources; (ii) provide the regulatory authority and other competent authorities with sufficient resources, including trained personnel, for the enforcement of compliance with relevant requirements;
(iii) consider installing and maintaining radiation monitoring systems at ports, at border crossings and at other locations where radiation sources might appear (such as metal scrapyards and recycling plants); (iv) develop adequate search and response strategies, and prepare and sign protocols between government agencies; and (v) arrange joint demonstration exercises for the training of staff.
Effective management of SRSs is vital to both safety and security, and we should always keep in mind that “prevention is better than remediation”.
ACKNOWLEDGEMENTS
The author acknowledges the contribution of S. Sanin and E. Tanker in reviewing this paper.
MANAGEMENT OF ORPHAN SOURCES
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63 COMMENTS BY THE CHAIRPERSON
T. TANIGUCHI (IAEA): At the beginning of his presentation, Mr. Uslu showed a chart depicting the increase in the number of sources identified, detected and reported. The IAEA Secretariat sees a need to clarify and analyse the causes, because this represents not only a possible increase of sources crossing borders but also an improvement in detection systems, notification, reporting and networking. The Secretariat appreciates the Turkish Government’s cooperation and also its support of work to identify sources in neighbouring countries such as Georgia.
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