1. 1. The Borehole Disposal Concept-An Option for Radioactive Waste Disposal A.M.A. Dawood (99550237752) Department of Environmental Engineering Anadolu University Eskisehir
2. 2. Order of Presentation: Introduction BDC As a Long-Term Management Solution For DSRS Safety Requirements For Disposal of DSRS Design of the BDC Operational Requirements of the BDC Closure, Decommissioning and Rehabilitation & Institutional Controls
3. 3. 1.0 Introduction Radioactive sources are widely used in most IAEA Member States, in various industrial, research and medical applications. These sources contain different radionuclides in widely varying quantities.
4. 4. 1.0 Introduction In some cases, the activity of the source decays to a level below which it is no longer suitable for its original purpose or the equipment may have become obsolete, worn out/damaged, or the source may develop a leak. In all these circumstances, the radioactive sources are referred to as disused or spent, even though their activity could still be very high.
5. 5. Intro Disused sealed radioactive sources (DSRS) pose a significant hazard to human beings and the environment in general if not managed properly. Management of radioactive waste involves tracking, retrieving, conditioning, characterizing, storing and eventual disposing of the disused sources. This process requires a high level of technical expertise is costly. The IAEA through its TC project with NECSA developed a simple and economically viable option for use by any interested member state; This option is termed the Borehole Disposal Concept (BDC).
6. 6. Intro The concept integrates source handling and conditioning on the surface and emplacement of the sources in an engineered borehole of narrow diameter (0.26m), Borehole depth ranges from 30 to 150 m below surface in a suitable geological environment. Disposal system made up of stainless steel capsule sealed in another container, also made from stainless steel.
7. 7. Intro
8. 8. 1.1 Waste management in perspective From storage to disposal:
9. 9. 1.1.1 Fundamental Principles agreed upon by the international community for the management of radioactive waste
10. 10. 2.0 BDC as a Long-term Management Solution for DSRS Disposal according to IAEA definition, is the emplacement of waste in an approved, specified facility, without the intention to retrieve the waste. This does not necessarily imply that the waste is not retrievable, rather there is no intention to retrieve the waste. The borehole disposal option uses the multiple concepts based on a system of several passive barriers; which consist of the conditioned and packaged waste, repository lining, back-filling and other engineered barriers within the borehole repository.
11. 11. waste packaged for disposal
12. 12. 2.0 BDC as a Long-term Management Solution for DSRS The Borehole Casing stabilizes the borehole and keeps the repository dry during the operational period while acting as additional barrier to transport of the radionuclides. Backfilling materials add additional barrier between the containers and aggressive chemicals, prominently chloride that might initiate corrosion of the stainless steel capsule. Schematic illustrations of the two low temperature (left and centre) and one high temperature (right) concepts defined by Gibb In high temperature concepts, HLW or SF is disposed of [very deep disposal] According to Gibb, the HTVDD concept is being less actively considered internationally than the low temperature concepts.
13. 13. DSRS The sorptivity nature of the backfilling material makes it act as a chemical buffer to intrinsically limit or reduce the release of radionuclides to the geosphere; It also form a physical and hydrological barrier through which leached radionuclides must pass before they are released into the immediate surroundings. The underlying common characteristic of the facility is its small physical size (footprint) at the surface, which reduces the likelihood of human intrusion.
14. 14. The BDC, apart from providing a potentially cost effective and safe disposal option for countries with limited nuclear infrastructure, it offers the following benefits: Provision of long-term isolation from humans and the environment for small volumes of high specific activity DSRS in high integrity waste packages; Provision of direct and cost effective access to a suitable geological horizon, using a readily available technology. In particular, an appropriate depth of disposal and geological horizon can be selected in a cost-effective manner; 3.0 Characteristics of the BDC
15. 15. It requires limited land area and limited infrastructure; It requires short periods of construction, operation and closure; It can be developed as and when required to dispose of DSRS as they arise; It has a low probability of human intrusion and future disruptive events due to the small footprint of the borehole and the ability to select a suitable depth; 3.0 Characteristics of the BDC
16. 16. 4.0 Design of the BDC Long-term safety of the borehole disposal facility is achieved through a combination of natural barriers, engineered barriers, operational procedures and institutional controls. The design and concept adopted depend on a number of factors: The number of sources to be disposed of; The type of sources that need to be disposed and their radionuclide content; The period of time over which the sources will arise and the facility will need to be operational; The availability of suitable disposal environments; The availability of appropriate drilling and engineering technologies; and availability of resources.
17. 17. 4.0 Design of the BDC The BDC design is an ab-initio process implemented from initiation through to completion. It informs the following activities: Suitable site selection: the site should have features which when combined with the facility and waste package design, provides adequate isolation of radionuclides from the biosphere for the required periods of time. Engineered waste package: refers to the product of conditioning that includes the waste container and container backfill material prepared in accordance with requirements for the disposal of DSRS.
18. 18. 4.0 Design of the BDC Container durability: the correct selection of container materials is essential for satisfactory performance of the concept; Their resistance to degradation and corrosion in long-term consideration which is a function of the waste characteristics. Other essential factors include; Container dimension, handling of containers, container shape, container backfill etc.
19. 19. 5.0 Safety Requirements for Disposal of DSRS One of the basic requirements of the borehole disposal concept is the implementation of measures that will afford the protection of human (workers and general public) and the larger environment as a function of time. Observance of internationally agreed fundamental principles of radioactive waste management (international principles). During the operational phase of the facility, safety can be assured by conventional operational radiation protection programmes; guided by relevant international standards (IAEA).
20. 20. 5.0 Safety Requirements for Disposal of DSRS Doses to workers and members of the public exposed as a result of operations at the disposal site shall be as low as reasonably achievable (ALARA), Relevant considerations during operation include: Separation of drilling and waste emplacement activities, Use of remote handling and shielded equipment for waste emplacement, Minimization of the potential for accidents and their consequences, and Minimization of maintenance requirements in radiation and contamination areas.
21. 21. 5.1 Legal and Organizational Framework Besides the development of the necessary technical and operational capability, safe management of radioactive waste is also promoted by the existence of an appropriate legal infrastructure. The development of a borehole disposal facility should therefore be carried out in compliance with any relevant national and international regulations.
22. 22. 5.1 Legal and Organizational Framework Particular consideration needs to be given to: Compliance with radiation protection criteria for occupationally exposed workers and members of the public in normal operation and accidents; Compliance with operational limits and conditions, with specific emphasis on waste acceptance criteria; Implementation of corrective actions in case deviations are detected; and Performance of adequate control of the disposal site (e.g. monitoring).
23. 23. 6.0 Operational Requirements of the BDC Before the commencement of construction of a repository, a comprehensive and systematic assessment of its safety throughout its operating lifetime and the period following closure, must be performed. The implementation of the borehole disposal concept in any country can be divided into several stages, which are embodiment of the concept and include the following: Site selection, site characterisation and data acquisition; Operational and long-term (post-closure) safety assessment of the borehole;
24. 24. 6.0 Operational Requirements of the BDC Conditioning of the sources into suitable waste packages; Transport of waste packages to disposal facility; Preparing the repository; Acceptance of waste packages at the repository; Emplacement of the waste packages in the repository; Closure of the repository; and Institutional controls.
25. 25. 7.0 Closure, Decommission and Rehabilitation & Institutional Controls Closure, decommissioning and rehabilitation of the repository will take place after the receipt of waste ceases and waste emplacement operations have been completed. Engineered barriers, particularly the final cover, are emplaced to ensure the integrity of the repository and minimize ingress of infiltrating water to the waste, thereby limiting radionuclide releases, and also to reduce the likelihood of disturbance by human activities. The closure can include the physical marking of the borehole, if required.
26. 26. 7.0 Closure, Decommission and Rehabilitation & Institutional Controls After repository closure, institutional controls are considered as an optional activity by the host country. The controls can be either active (for example, monitoring and surveillance) or passive (for example, land use control and record keeping). Controls maintained over a repository after closure are designed to enhance its safety, in particular, by preventing intrusion into the disposal units.
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