Disposal of Disused Radiation Sources: International Standards and Their Implementation in Ukraine
Radiation sources are widely used in various fields of human activities. They are used for diagnosis and treatment of cancer and other diseases in medicine and to check integrity and density of materials, perform various measurements and receive energy from radioisotope thermoelectric generators (RTG) in industry.
In geology, radiation is applied for shaft and borehole logging during the search for minerals or study of the geological structure of the area. Scientists need radiation to conduct research, while farmers apply it to measure soil moisture and sterilize agricultural products (grain, vegetables, fruit, etc.).
Smoke detectors of the old model include radiation sources, which can still be found in old industrial buildings.
If the radionuclides in radiation sources are short lived (conditionally their half-life is less than 10 days, for example iodine-131, technetium-99m, etc.), such a source in a short time ceases to be dangerous to humans and the environment. Therefore, relevant preparatory activities are carried out with radiation sources when they are out of service (life expiration) to dispose them as household waste. This approach is applied to disused radiation sources in medicine and it is regulated by the General Radiation Safety Rules for Radiation Sources in Medicine (2017).
For example, medical radiopharmaceuticals (including those based on the mentioned iodine-131 and technetium-99m) are stored in a special tank during the half-life. After this, they are diluted with water in a ratio of 1:10, and then drained into the sewer. Besides, the medical institution must conduct radiation monitoring of wastewater so that the total discharge of radioactive substances into water reservoir does not exceed the established permissible level.
If more than 200 liters of liquid radioactive substances are generated per day, there must be a separate sewer for them in the institution. If less – substances are collected in special tanks and stored until their activity decreases to the levels of clearance from regulatory control. The same procedure is envisaged if it is not possible to dilute these substances with non-radionuclide wastewater.
The medical institution shall return technetium generators after use to the supplier. If it is not possible, they shall be stored in special containers during ten half-life periods (1.5 – 2 months), after which they become non-radioactive materials and are disposed of as ordinary waste.
Various solid waste with traces of radiopharmaceuticals (used syringes, needles, vials, napkins, gloves, etc.) is collected in separate containers until the container is filled. The container is then sealed and stored until the absorbed dose rate in the air at a distance of 0.1 m from the accessible parts of the container surface does not exceed the values of the background radiation of its location.
However, the presence of long lived radionuclides in radiation sources does not allow treating them as household waste, because, as a rule, the service life of such sources (both in terms of safety and in terms of functions) is significantly shorter than the time during which they pose a danger. An indicative list of the most common ling lived radionuclides used in industry, medicine and research is presented in the Table:
|Main applications of sealed radioactive sources, radioisotopes used and their half-lives|
|Medicine (teletherapy, brachytherapy, nuclear pacemakers)||60Co
|Geology (well logging/soil moisture gauges)||137Cs
|Source: Disposal Options for Disused Radioactive Sources. International Atomic Energy Agency. Vienna, 2005|
Radioactive Waste Management Strategy of Ukraine (valid since 2010) provides that “the state promotes the reuse or processing of radiation sources when it is practically possible and compatible in terms of safety and security”. If it is not possible to extend service life or restore disused radiation sources, they shall be disposed of as radioactive waste to which they are referred by the Law of Ukraine “On Radioactive Waste Management” in the latest revision of 2019. The national General Safety Rules for Predisposal Management of Radioactive Waste) (2017) state that disused radiation sources are transferred to solid radioactive waste.
International recommendations on disposal of disused radiation sources referred to radioactive waste category
According to IAEA estimates, about 20 % of the millions of radiation sources produced worldwide are referred to disused ones. The world practice considers several options for disposal of disused radiation sources: in disposal facilities with other radioactive waste or in separate disposal facilities constructed specifically for radiation sources. However, the latter option does not preclude the possibility of placing both storages on the same site under certain conditions.
The algorithm of management of disused radiation sources envisages first the need to assign disused source to a certain class of radioactive waste. “When disused radiation sources become radioactive waste, all safety principles of radioactive waste management shall be applied to them. The difficulty lies in the fact that approaches to the classification of radiation sources and radioactive waste are significantly different”, said Oleksiy Tokarevsky, Kateryna Fuzik, Sergiy Kondratiev and Zoya Alekseyeva, experts of the State Scientific and Technical Center for Nuclear and Radiation Safety (SSTC NRS).
In the case of radiation sources, they are classified according to five categories depending on the risk to human health that the source may pose in the event of loss of control over it. The highest risk means the first category and the lowest risk, respectively, means the fifth category.
Classification of disused radiation sources
|Category||Radiation source hazard||Examples|
|1||Extremely hazardous to human health||RTGs, panoramic irradiators|
|2||Very hazardous to human health||Industrial gamma radiography projectors,
high/medium dose rate brachytherapy machines
|3||Hazardous to human health||Fixed industrial gauges, well logging gauges|
|4||Potentially safe to human health||Bone densitometers, level gauges|
|5||Most likely safe to human health||Permanent implants,
|Source: IAEA. Status and Trends in Spent Fuel and Radioactive Waste Management. Vienna, 2018|
The approach to radioactive waste classification according to IAEA recommendations is different. Radioactive waste is divided into categories compliant to the way of disposal:
|Exempted waste (EW)||Waste that meets the criteria for clearance, exemption or exclusion from regulatory control for radiation protection purposes.||Ordinary landfills for household or industrial waste.|
|Very short lived waste (VSLW)||Waste that can be stored for decay over a limited period of up to a few years and subsequently cleared from regulatory control according to arrangements approved by the regulatory body, for uncontrolled disposal, use or discharge. This class includes waste containing primarily radionuclides with very short half-lives often used for research and medical purposes.||Ordinary landfills for household or industrial waste.|
|Very low level waste (VLLW)||Waste that does not necessarily meet the criteria of exempt waste, but that does not need a high level of containment and isolation. Typical waste in this class includes soil and rubble with low levels of activity concentration. Concentrations of longer lived radionuclides in VLLW are generally very limited.||Disposal in near surface disposal facilities of trench types with limited regulatory control (in which other types of hazardous waste can be stored as well). Barriers of such disposal facilities shall ensure keeping and confinement of radioactive waste for a period not less than 100 years after disposal facility closure. The duration of administrative control shall not exceed 100 years (and 300 years for disposal facilities in the exclusion zone).|
|Low level waste (LLW)||Waste that is above clearance levels, but with limited amounts of long lived radionuclides. Such waste requires robust isolation and containment for periods of up to a few hundred years. This class may include short lived radionuclides at higher levels of activity concentration, and also long lived radionuclides, but only at relatively low levels of activity concentration.||Disposal in engineered near surface disposal facilities (matrix, container, other sealing means) at a depth of several tens of meters, capable of keeping and confinement of radioactive waste not less than during 300 years after disposal facility closure.|
|Intermediate level waste (ILW)||Waste that may contain long lived radionuclides, in particular, alpha emitting radionuclides that will not decay to a level of activity concentration acceptable for near surface disposal during the time for which institutional controls can be relied upon.||Disposal at greater depth from tens to several hundred meters. The system of disposal facility barriers shall ensure keeping and confinement of radioactive waste not less than during several thousand years after the closure of the disposal facility.|
|High level waste (HLW)||Waste with levels of activity concentration high
enough to generate significant quantities of heat by the radioactive decay
process or waste with large amounts of long lived radionuclides.
|A generally accepted method of disposal is disposal in stable geological repositories several hundred meters or more deep. The system of barriers shall ensure keeping and confinement of radioactive waste during a long term period after the closure of the disposal facility taking into account heat release due to natural decay of radionuclides.|
|Source: International Atomic Energy Agency, Classification of Radioactive Waste, IAEA Safety Standards Series No. GSG-1, IAEA, Vienna (2009). Загальні положення безпеки при захороненні радіоактивних відходів (2018).|
Therefore, each specific disused radiation source shall be correlated with a certain class of radioactive waste to define the acceptable way of its disposal. The following diagram illustrates the possible way out:
Illustration of the waste classification scheme application to disused radiation sources
Characteristics of disused radiation sources used in the diagram
|Symbol on the diagram||Half-life||Activity||Volume||Example|
|i||< 100 d||100 MBq||Small||Y-90, Au-198 (brachytherapy)|
|ii||< 100 d||5 PBq||Small||Ir-192 (brachytherapy)|
|iii||< 15 a||< 10 MBq||Small||Co-60, H-3 (tritium targets), Kr-85|
|iv||< 15 a||< 100 MBq||Small||Co-60 (medical irradiators)|
|v||< 30 a||< 1 MBq||Small||Cs-137 (brachytherapy, moisture density detectors)|
|vi||< 30 a||< 1 MBq||Small||Cs-137 (medical irradiators), Sr-90 (thickness gauge, RTGs)|
|v ii||> 30 a||< 40 MBq||Small, but may be large numbers of sources (up to tens of thousands)||Pu, Am, Ra (static eliminators)|
|viii||> 30 a||< 10 PBq||Am-241, Ra-226 (gauges)|
What are the real possibilities for disposal of disused radiation sources in Ukraine?
In Ukraine, most of disused radiation sources, which are not subject to restoration or return to the manufacturer, are transferred to radioactive waste category and shall be submitted for storage to the interregional specialized plants of the State Specialized Enterprise “Radon Association”. According to the data of the Chief Information and Analytical Radwaste Accounting Center of the Radon Association, 641 130 disused radiation sources declared as radioactive waste with a total activity of 2.71·1016 Bq have been stored in the facilities of the state interregional plants of the Radon Association as of 31 December 2019. The main part of this volume has been accumulated on Radon sites since 1960.
At present, specialized plants of the Radon Association are converted into sites for collection and intermediate container storage of disused radiation sources. According to General Safety Provisions for Predisposal Management of Radioactive Waste, the following management of disused radiation sources is envisaged there:
- sorting for separate storage depending on the half-life of radionuclides, radiation type and activity;
- placement for storage in specially designated packaging;
- storage of disused radiation sources separately from other radwaste.
The Centralized Storage Facility for Disused Radiation Sources (CSFDRS) was constructed on the Vektor site in the exclusion zone in 2015 for long term storage. It is intended for acceptance, identification, characterization, sorting, processing, certification, conditioning and further storage of disused radiation sources referred to radioactive waste.
In the future, CSFDRS will be able to accept 500 thousand units of radiation sources with a total activity of up to 3.7⋅1016 Bq for a period of 50 years. Therefore, they will still need to be transferred for disposal into disposal facilities according to the class of radioactive waste to which they will be referred.
In the meantime, the operating organization (Centralized Enterprise for Radioactive Waste Management) carries out hot tests at the facility to ensure its compliance with all necessary safety criteria for the management of radioactive waste in the form of disused radiation sources.
If one speaks about the construction of a separate disposal facility exclusively for disused radiation sources, IAEA recommendations recognize the borehole type as the most appropriate option for its design in terms of protection, simplicity and cost efficiency. The disposal facility of such a type can have different depth depending on the desired level of keeping and confinement, which meets requirements similar to those for low level waste or intermediate level waste. However, there are no plans to construct a separate borehole disposal facility in Ukraine to date.
Apart from the Buriakivka disposal facility designed exclusively for Chornobyl origin radioactive waste, the system of radioactive waste disposal in Ukraine is represented by one operating facility on the Vektor site that is the Engineered Near Surface Disposal Facility for Solid Radioactive Waste, which has been in operation since 2008. The disposal facility was designed to accept 55 thousand cubic meters of low level radioactive waste for disposal (according to the new Ukrainian classification), but it currently has a SNRIU license for the operation of two out of 22 compartments.
Two other near surface disposal facilities for solid radioactive waste with a total capacity of 19 200 m3 are at the final stage of construction (acceptance tests of systems and equipment are planned) on the Vektor site: SRW-1 is the facility for disposal of short lived low and intermediate level radioactive waste in reinforced concrete containers (acceptance capacity of 9800 m3) and SRW-2 is the facility for disposal of short lived low and intermediate level large, bulk radioactive waste, radioactive waste in drums, craft bags (shape forming package), cargo cages (9400 m3).
However, near surface disposal facilities do not solve the problem of disposal of disused radiation sources completely. First, according to the results of hot tests at CSFDRS on the example of sources with cobalt-60 and cesium-137, activity levels of packages do not comply with the criteria for acceptance of near surface disposal facilities at the time of disposal facility closure. In addition, the type of packages intended for conditioned disused sources at CSFDRS is not suitable for disposal in all existing and designed Vektor facilities. Engineered Near Surface Disposal Facility is intended for radioactive waste disposal in KTZ-3.0 packages (reinforced concrete containers) and 200-l drums. SRW-1 envisages disposal only in reinforced concrete containers. Conditioning of sources at CSFDRS is not provided in these two types of packages. The only disposal facility of the above that could theoretically accept packages with disused radiation sources is SRW-2, which provided for the placement of radioactive waste in bulk. This can be possible only if they meet the acceptance criteria of this disposal facility.
Before conditioning, disused radiation sources at CSFDRS are sorted according to the criteria that take into account further disposal options. Oleksii Tokarevskyi and colleagues present three types of disused radiation sources, the division into which is provided by the sorting criteria during the hot tests:
- disused radiation sources in the package, which meet the acceptance criteria of the near surface disposal facility at the time of package forming (type A);
- disused radiation sources in the package, which will meet the acceptance criteria of the near surface disposal facility at the moment of CSFDRS closure (type B);
- disused radiation sources in the package, which will not meet the acceptance criteria of the near surface disposal facility at the moment of CSFDRS closure (type C).
Test results indicate that the test samples of packages with disused radiation sources with cesium-137 and cobalt-60 isotopes belong to type C meaning that they will not meet the acceptance criteria of the near surface disposal facility at the moment of CSFDRS closure.
“It is possible to predict that in the case of further application of existing criteria for sorting of disused radiation sources, the vast majority of packages of disused radiation sources from CSFDRS will require disposal in deep geological repositories. Such a prospect is undesirable because the cost of disposal in deep geological repositories is very high and directly depend on the capacity of the disposal facility and disposal depth”, SSTC NRS experts commented.
Therefore, the experts concluded that it is now important to realistically assess the possibility for disposal of disused radiation sources in near surface disposal facilities that means accurate definition of their specific activity for a long-term period.
Prospects of geological disposal
Sooner or later deep geological repositories will have to be built, since certain classes of radioactive waste (including in the form of disused radiation sources) can be safely disposed only there. Moreover, the Radioactive Waste Management Strategy envisages the need for the construction of such a repository.
IAEA document refer to the creation of underground facilities in the form of shafts of 200-1000 m deep or boreholes of 3-5 km deep. Natural deposits of granite, clay, salt, etc. and engineered barriers will be applied as radiation barriers in such a repository. Defense in depth will ensure radioactive waste confinement for thousands of years and more.
However, the construction of such a repository involves a lot of time for preparation, design and construction, as well as considerable financial resources.
What the deep geological repository for spent nuclear fuel Onkalo (Finland) looks like inside
A specific design to construct a geological repository in Ukraine has not yet been developed. Since 1993, experts of the Geological Service, Institute of Geological Sciences of the National Academy of Sciences of Ukraine together with regulatory authorities on nuclear and radiation safety and international organizations have been searching for a suitable site for such a repository. Screening of saline, clay, crystalline formations and spent iron ore mine Saksagan (Kryvy Rig) showed that crystalline rocks in the exclusion zone or near it are the most reasonable location.
Stella Shekhunova, Deputy Director of the Institute of Geological Sciences of the National Academy of Sciences of Ukraine, named the presence of Chornobyl origin radioactive waste, developing infrastructure for other radioactive waste and spent nuclear fuel, absence of permanently living people, favorable protective properties of host rocks and overlying strata the advantages of this territory.
Currently, there are three promising locations for siting of a deep geological formation (see Figure): Zhovtneva site (southwestern areas of Chornobyl exclusion zone) and Veresnianska site (outside Chornobyl exclusion zone adjacent to it) and Novosilky (areas south of the Prypiat city). However, field research directly on these locations and further steps on the final siting are still ahead. Once the siting has been completed, there are 30 years for the design, construction and commissioning of the disposal facility in deep geological formations according to the Radioactive Waste Management Strategy. There are great doubts that Ukraine will cope with the task within this period.
“It can be assumed that all packages with radioactive waste in the form of disused radiation sources, the activity of which will exceed the limits set in the criteria for radioactive waste acceptance in near surface disposal facilities, will be transferred for disposal to the deep geological repositories”, O. Tokarevsky and colleagues predicted.
Thus, there is a large amount of disused radiation sources in Ukraine, both modern and those inherited from the USSR. Most of them were transferred to plants of the Radon Association and referred to the category of radioactive waste, so their disposal is provided by the same criteria.
As disused radiation sources have their differences from other types of radioactive waste, in particular, high specific activity, it is very important to ensure safe management of disused radiation sources transferred to the category of radioactive waste at all stages, including the stage of disposal. At the same time, specific facilities in which disposal of disused radiation sources is envisages have not been clearly defined, as well as the criteria for acceptance of disused radiation sources for disposal have not been established.
At present, the nearest prospect is to complete the commissioning of CSFDRS and transfer of disused radiation sources from the plants of the Radon Association to it in compliance with all nuclear and radiation safety requirements. During 50 years of operation, CSFDRS will have to developed a comprehensive approach to their safe storage, in particular: to improve sorting of disused radiation sources taking into account future disposal, define specific disposal facilities for this and acceptance criteria for disused radiation sources.
From the editorial board:
Meantime, it is necessary to work to ensure that disused radiation sources are transferred to specialized plants of the Radon Association and then to CSFDRS taking into account all safety measures. Peculiar attention shall be paid to the search of lost radiation sources, which are beyond regulatory control due to the decline of certain enterprises, liquidation of organization, etc. Anyone who knows the location of such a source can help experts, especially since the voluntary surrender of a radioactive object is not prosecuted. Visit the website “STEP to safety” to find out what to do and whom to contact.
Uatom.org Editorial Board