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2.9.2 Management of radioactive waste

Contents Definition of radioactive waste classes by the IAEA Exempt waste (EW) Low and intermediate level waste (LILW) Additional considerations Key issues for waste management On-site facilities for management of radioactive wastes Operational nuclear-licensed sites Non-nuclear-licensed sites On-site segregation of wastes for radioactivity Definition of radioactive waste classes by the IAEA

In the context of site investigations on potentially radioactively contaminated sites, wastes fall into two categories: radioactive waste and non-radioactive waste.
The definition of radioactive and non-radioactive wastes is given in national legislations and these can vary from country to country.

Exemption orders of both types of wastes exist that specify the conditions under which materials or wastes defined as radioactive can be “exempted”, i.e., excluded from some or all of the regulatory provisions for radioactive materials. It is advised to check the national regulations on this topic.

The IAEA has defined the following radioactive waste categories (see Table 2.9) [IAEA-1994].

Waste classes Typical characteristics Disposal options

1 Exempt waste (EW) Activity levels at or below clearance levels [IAEA-1996a], which are based on an annual dose to members of the public of less than 0.01 mSv No radiological restrictions

2 Low and intermediate level waste (LILW) Activity levels above clearance levels [IAEA-1996a] and thermal power below about 2 kW/m3

2.1 Short lived waste (LILW-SL) Restricted long lived radionuclide concentrations (limitation of long lived alpha emitting radionuclides to 4000 Bq/g in individual waste packages and to an overall average of 400 Bq/g per waste package)

Near surface or geological disposal facility
2.2 Long lived waste (LILW-LL) Long lived radionuclide concentrations exceeding limitations for short lived

Geological disposal facility.
3 High level waste (HLW) Thermal power above about 2 kW/m3 and long lived radionuclide concentrations exceeding limitations for short lived waste

Geological disposal facility

Table 2.9 Radioactive waste classes as proposed by IAEA Exempt waste (EW)

Exempt waste (EW) contains so little radioactive material that it cannot be considered ‘radioactive’ and might be exempted from nuclear regulatory control. That is to say, although still radioactive from a physical point of view, this waste may be safely disposed of, applying conventional techniques and systems, without specifically considering its radioactive properties [IAEA-1994].

Many studies have been performed on the subject of waste exemption. The IAEA provides recommendations on exemption from regulatory control and specifies unconditional clearance levels for radionuclides in solid materials based on limiting annual doses to members of the public to 0.01 mSv [IAEA-1996a]. The recommended activity concentrations are dependent on the individual radionuclide and range from about 0.1 Bq/g to about 104 Bq/g. Because possible individual radiation doses are trivial at these concentrations, no particular attention needs to be paid to the radioactive properties of such waste.

Levels of activity concentration for exempt waste higher than those suggested in [IAEA-1996a] may be established by the national authority on a case-by-case basis if specific national peculiarities are considered or defined requirements or conditions are given for the exemption of waste. The levels of activity concentration appropriate for conditionally exempt waste are highly dependent on the conditions for exemption. Actual values can be derived for individual cases.

It is important to obtain a consensus on the boundary for unconditionally exempt material which may be transferred from one country to another (e.g., for recycle/reuse). It would be of great value if the same limits could be adopted for different sites. This would greatly simplify exemption procedures and would increase the confidence of the public in such practices. Low and intermediate level waste (LILW)

Low level waste has been defined in the past to mean radioactive waste that does not require shielding during normal handling and transportation [IAEA-1994]. Radioactive waste which required shielding but needed little or no provision for heat dissipation was classified as intermediate level waste. A contact dose rate of 2 mSv/h was generally used to distinguish between the two classes.

This distinction appears of secondary importance in the present context. Classification should be related to individual radionuclides, taking the various exposures and exposure pathways into account, such as inhalation (e.g., in the case of an incident) and ingestion (e.g., in the case of long term releases in the post-operational period of a repository). Thus, low and intermediate level waste may be subdivided into short-lived and long-lived waste. Additional considerations which must be taken into account in managing low and intermediate level waste are presented subsequently under ‘Additional Considerations’.

  • Short-lived waste (LILW-SL). Short-lived low and intermediate level waste (LILW-SL) contains low concentrations of long-lived radionuclides. The possible hazard represented by the waste can often be significantly reduced by administratively controlling waste as part of storage or after disposal. Although the waste may contain high concentrations of short-lived radionuclides, significant radioactive decay occurs during the period of institutional control. Concentrations of long-lived radionuclides that will not decay significantly during the period of institutional control are controlled to low levels consistent with the radiotoxicity of the radionuclides and requirements set forth by national authorities.

Because LILW-SL may be generated in a wide range of concentrations, and may contain a wide range of radionuclides, there may be a range of acceptable disposal methods. The waste form or packaging may also be important for management of this waste. Depending upon safety analyses and national practices, these methods may range from simple surface landfills, to engineered surface facilities, and to disposal at varying depths, typically a few tens of metres, or in deep geological formations if a co-disposal of short- and long-lived waste is anticipated. National practices may impose varying levels of isolation depending upon the hazard represented by different classes of radioactive waste.

From existing criteria it appears that a general boundary between near surface and geological disposal of radioactive waste cannot be provided, as activity limitations will differ between individual radionuclides or radionuclide groups and will be dependent on the actual planning for a near surface disposal facility (e.g., engineered barriers, duration of institutional control, site specific factors).

  • Long-lived waste (LILW-LL). Long-lived low and intermediate level waste (LILW-LL) contains long-lived radionuclides in quantities that need a high degree of isolation from the biosphere [IAEA-1994]. This is typically provided by disposal in geological formations at a depth of several hundred metres.

The boundary between short-lived and long-lived waste cannot be specified in a universal manner with respect to concentration levels for radioactive waste disposal, because allowable levels will depend on the actual radioactive waste management option and the properties of individual radionuclides. However, in current practice with near surface disposal in various countries, activity concentration is limited to 4000 Bq/g of long-lived alpha emitters in individual radioactive waste packages, thus characterizing long-lived waste which is planned to be disposed of in geological formations. This level has been determined based on analyses for which members of the public are assumed to access inadvertently a near surface repository after an active institutional control period, and perform typical construction activities (e.g., constructing a house or a road).

Applying this classification boundary, consideration should also be given to accumulation and distribution of long-lived radionuclides within a near surface repository and to possible long term exposure pathways. Therefore, restrictions on activity concentrations for long-lived radionuclides in individual waste packages may be complemented by restrictions on average activity levels or by simple operational techniques such as selective emplacement of higher activity waste packages within a disposal facility. An average limit of about 400 Bq/g for long-lived alpha emitters in waste packages has been adopted by some countries for near surface disposal facilities.

In applying the classification system, attention should also be given to inventories of long-lived radionuclides in a repository that emit beta or gamma radiation. For radionuclides such as 129I or 99Tc, allowable quantities or average concentrations within a repository depend strongly on site specific conditions. For this reason, national authorities may establish limits for long-lived beta and gamma emitting radionuclides based on analyses of specific disposal facilities.

  • High level waste (HLW). The high level waste (HLW) class largely retains the definition of the existing classification system [IAEA-1994]. This waste contains large concentrations both of short- and long-lived radionuclides, so that a high degree of isolation from the biosphere, usually via geological disposal, is needed to ensure disposal safety. It generates significant quantities of heat from radioactive decay, and normally continues to generate heat for several centuries.

An exact boundary level is difficult to quantify without precise planning data for individual facilities. Specific activities for these waste forms are dependent on many parameters, such as the type of radionuclide, the decay period and the conditioning techniques. Typical activity levels are in the range of 5 × 104 to 5 × 105 TBq/m3, corresponding to a heat generation rate of about 2 to 20 kW/m3 for decay periods of up to about ten years after discharge of spent fuel from a reactor. From this range, the lower value of about 2 kW/m3 is considered reasonable to distinguish high level waste from other radioactive waste classes, based on the levels of decay heat emitted by high level waste such as those from processing spent fuels.

The suggested boundary levels for high level waste need not be distinct because of the general consensus that a high degree of isolation is necessary for management of radioactive wastes having very high concentrations of short- and long-lived radionuclides. National programmes exist to manage such radioactive waste. Additional considerations

A number of additional important factors should be considered when addressing specific types or properties of radioactive waste [IAEA-1994].

  • Waste containing long-lived natural radionuclides. Many countries must address the disposal of very large quantities of waste containing long-lived natural radionuclides. Such waste typically contains natural radionuclides like uranium, thorium, and radium and is frequently generated from uranium/thorium mining and milling or similar activities. It may also include waste from decommissioning of facilities, where other isotopes may also be present. The characteristics of these wastes are sufficiently different from other wastes that they may require an individual regulatory approach.

Although these wastes do contain long-lived radionuclides, their concentrations are generally sufficiently low that either they can be exempted or disposal options similar to those for short-lived waste may be considered, depending on safety analyses.

  • Heat generation. Although heat generation is a characteristic of high level radioactive waste, other radioactive wastes may also generate heat, albeit at lower levels. Heat generation is dependent upon the type and content of radionuclides (half-life, decay energy, etc.). Furthermore, the heat removal situation is highly important (thermal conductivity, storage geometry, ventilation, etc.). Therefore, heat generation cannot be defined by a single value. The relevance of heat generation can vary by several orders of magnitude depending on the influencing parameters and the temperature limitations. Management of decay heat should be considered in a repository if the thermal power of waste packages reaches several W/m3. Especially in the case of long-lived waste, more restrictive values may apply.
  • Liquid and gaseous waste. The treatment of liquid waste (which may contain paniculate solids) and gaseous waste (which may contain aerosols) aims at separating the radionuclides from the liquid or gaseous phase and concentrating them in a solid waste form. The separation is pursued until the residual concentration or total amount of radionuclides in the liquid or gaseous phase is below limits set by the regulatory body for the discharge of liquid or gaseous waste from a nuclear facility as an effluent. Treatment may include a storage period for radioactive decay.

Liquid and gaseous radioactive waste exceeding discharge limits set by national authorities should be conditioned for storage, transport and disposal. Only following sound safety analysis should radioactive waste in liquid or gaseous form be transported off the site or disposed of in terrestrial repositories in their original forms. Storage for decay at the facility of their origin may be considered as part of the conditioning process.

The classification of liquid and gaseous radioactive waste may be based on the different types of treatment that can be used, and on potential radiological, chemical and biological hazards. When solidified or conditioned for disposal these wastes fall under one of the solid radioactive waste classes. Key issues for waste management

The key issues for waste management on radioactively and potentially radioactively contaminated sites are summarized below.

  • Averaging volume. This is the volume of waste over which the activity concentration of radionuclides is averaged. Categorisation of waste (see below) is made on the basis of the averaging volume, which is therefore a key parameter in the design of a site characterization and any subsequent remediation. The averaging volume of any waste produced from the site characterisation or subsequent remediation should be agreed with the relevant environment agency during the survey design stage. In practice this agreement will be established on a case-by-case basis.
  • Waste minimisation. Operators of nuclear-licensed sites will have both environmental policies and site licence conditions that state that waste production should be minimised. Strategies for intrusive investigations and for other aspects of the site investigation should be selected with this requirement in mind.
  • Categorisation of wastes. Definition is firstly in terms of radioactivity but should also include other aspects, such as the water or leachable oil content of solid wastes and the hydrocarbon content of liquid wastes. Ensure that disposal routes are available for all wastes that will be produced.
  • Define responsibilities for wastes. Define responsibilities for the characterisation, packaging and storage/disposal of radioactive and non-radioactive wastes. Note that this applies both to wastes produced on the site and to wastes arising from the laboratory analysis of samples.
  • Waste segregation. Health physics monitoring during the site investigation should be used to make an initial segregation into the radioactive and non-radioactive waste streams required by the site operator. Waste segregation is crucial to minimise production of radioactive wastes.
  • Confirmatory analysis of wastes. Prior to final sentencing of waste, laboratory analysis should be undertaken to confirm the waste category, and to ensure it conforms to acceptance criteria.
  • Waste disposal. Ensure that wastes are disposed in accordance with site operating procedures (if available) and legislation. Ensure duty of care for non-radioactive wastes.
    The level of relative enhancement of any wastes above background levels needs to be determined. Cases have arisen where elevated natural levels of radiation have resulted in problems over the sentencing of waste arising.

Some of the mentioned issues are dealt with in more detail below. On-site facilities for management of radioactive wastes Operational nuclear-licensed sites

Operational nuclear-licensed sites will have in general facilities for the management of both solid and liquid radioactive wastes. Typically on such sites, the site operator will retain responsibility for the storage and ultimate disposal of any solid radioactive wastes produced during the site investigation.

Under this arrangement, the contractor would be responsible only for the packaging of the solid radioactive wastes, in containers to be approved by the site operator. It would be for the site operator to ensure that disposal routes are available for both solid and liquid radioactive wastes; this may include obtaining variations to existing authorisations under the applicable regulations.

Facilities for the treatment and disposal of many liquid wastes are available on operational nuclear-licensed sites. Different categories of liquid waste are primarily defined by radioactivity limits. However, because the waste treatment plants will have been designed to treat the principal waste streams produced during routine operations on the site, and not with contaminated land investigations in mind, there may be the requirement to pre-treat site investigation wastes before disposal in the liquid effluent treatment plant. Pre-treatments may involve reducing suspended solid load, by processes such as flocculation/coagulation, settling and filtration, and reduction of dissolved or free-phase hydrocarbon or solvent contamination, by treatment with granular activated carbon. It is important to determine the waste acceptance criteria for liquid wastes, and hence the requirements for any pre-treatment, during the planning phase of the site investigation. Non-nuclear-licensed sites

On non-nuclear-licensed sites where no facilities are available for the treatment or disposal of solid or liquid radioactive wastes, the site owner will need to make appropriate plans and arrangements, and obtain the necessary authorizations and agreements for waste accumulation and disposal. The treatment and packaging requirements for solid wastes will depend on the route for their eventual disposal. A mobile effluent treatment plant may be required if authorisation cannot be obtained for direct discharge of liquid wastes to the waste storage or treatment plant or into the environment. On-site segregation of wastes for radioactivity

The radionuclide fingerprint of the potentially contaminated material must be known in order to select appropriate instruments and methodologies for assigning wastes to the different categories. Wastes in which fission products (such as 137Cs) or radium are the principal contaminants can be segregated using certain hand-held gamma detectors, for example a 3 inch x 3 inch sodium iodide detector. Calibration of the detector for the particular nuclide and geometry (e.g., a semi-infinite plane or an excavator bucket full of waste) will be required.

It is not adequate or appropriate to segregate alpha- or beta-contaminated wastes using hand-held instrumentation. It will either be necessary to use an on-site laboratory to carry out gross alpha and gross beta screening analysis of representative samples of the waste or to categorise wastes after the laboratory radiochemical analyses of soil samples become available.