Waste package specification and waste acceptance criteria

The waste package as a final product of RAW processing, prepared and ready for long-term storage, or disposal, consists of two components: the waste form and the waste container. In some cases there are also additional barriers or shielding used to increase the safety features of the waste package. The waste package should be prepared in a form corresponding to the requirements for handling, transport, storage and disposal.

A wasteform is defined as ‘radioactive waste after treatment and condi­tioning, usually in solid form, prior to its packaging into the waste con­tainer’. A waste container is defined as ‘the vessel into which the waste form is placed for future handling, storage and disposal’. The waste container fulfils the role of a protective barrier and shielding tool. The waste container should guarantee the tightness for the entire period of storage and/or dis­posal of the waste.

To ensure the long-term safety of waste disposal, WAC should be devel­oped based on a safety assessment of the considered disposal options and should be approved by the relevant authorities. Waste acceptance require­ments (criteria) are by definition quantitative or qualitative criteria for processed RAW to be accepted by an operator of a repository for disposal, or by an operator of a storage facility for storage. WAC are specified by the relevant authorities, or proposed by an operator and approved by the rel­evant authorities. Waste acceptance requirements might include, for example, restrictions on the activity concentration, or the total activity of particular radionuclides (or types of radionuclide) in the waste, or require­ments concerning the waste form or waste package [10]. In the past, the term waste acceptance criteria was only applied and used in the context of waste disposal. Later on, the approach to specify WAC has been extended also to some other steps of the waste life cycle — in particular, for transport and storage. In general, WAC can be specified for any foreseen waste man­agement operation and handling. WAC can prescribe and cover various waste package features and properties, such as: [2]

• requirements for waste container (e. g., design features, mechanical sta­bility, thermal resistance and also some additional features — shielding, corrosion protection, etc.);

• limitations for activity — permissible activities of individual radionu­clides, total activity, activity of selected critical radionuclides;

• radiological safety parameters — surface dose rates, surface contamination.

There are usually several other requirements, developed and specified based on the safety assessment of risks of the planned operations (trans­port, storage, disposal, etc.) with prepared waste packages. A more detailed description of this subject can be found in Chapter 3.

WAC are site-specific, but not container-specific. They are developed based on a safety assessment of the design and implementation of the waste disposal or waste storage facility and eventually waste transport tools. WAC are general criteria, usually not specified for particular waste containers and/or waste packages. Therefore they are not simply applicable in every­day technological practice.

To overcome the above limitations of WAC, the general waste acceptance requirements are usually transformed into detailed waste package specifica­tions (WPS). WPS should be developed and individually implemented for each type of RAW package and should reflect specific characteristics of the waste package. WPS are therefore waste package (and also waste con­tainer) specific and they are normally substantially more detailed than WAC. They shall be a consistent part of the QA/QC system applied by the waste package producer. Application of WPS allows simple control and verification of waste packages for both the waste producer as well as the waste disposal facility operator. Compliance of waste packages with WPS is considered a guarantee of compliance of said waste package with the WAC for a particular waste lifetime step. More details and guideline for development of WPS can be found in Ref. [11].

Waste acceptance criteria for disposal can normally be developed based on the safety assessment of an available, already constructed, or intended waste disposal facility. In any case, a clear idea of the waste disposal option should be available. However, many countries are in the situation where processing of RAW is unavoidable and the decision regarding a disposal facility is still deferred. In such cases, there are two principal options on how to proceed with waste processing to avoid future complications with acceptance of waste packages at the disposal site:

• Develop and apply generic WAC, based on international experience, approaches, and analogy with similar nuclear programmes. In this manner, a sufficiently conservative approach shall be taken and it shall be demonstrated that a national waste management policy and vision of future disposal options had been considered. These criteria can then be used for development of waste package specifications for available waste management technologies and waste packages already in use.

• Develop and apply only waste package specifications for particular waste streams and waste processing technologies, based on a detailed analysis of potential disposal options. A sufficiently conservative approach and margins in critical parameters shall be applied to avoid future problems with acceptance of waste packages for disposal.

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