Release criteria determine the radiological end-state of a remediated site and consequently the extent of remediation works and the amounts of waste generated. The IAEA have published a safety standard on release of

sites from regulatory control on termination of practices (IAEA, 2006b). Further guidance and examples are given in a Technical Document (IAEA, 2012). The safety standard represents good practice from within the IAEA member states and can be used as a guide by states when establishing their arrangements and regulations. Regulating the release of sites is a national responsibility.

The IAEA standard uses the term ‘practice’ to refer to any human activ­ity that introduces additional sources of exposure or exposure pathways to people. The standard applies to cases where there is a proposal to release sites from the requirements for radiation protection of the appropriate regulatory body because practices have ceased.

The IAEA standard establishes an approach whereby target dose criteria are compared to a prospective effective dose assessment for a critical group of the public, above the pre-practice background levels, of that dose received after the site has been released for defined new uses. The dose assessed is the summed effective dose arising from the land, buildings and other sources that remain at the point of site release or licence termination.

The radiological protection principles of justification, dose limitation and optimization apply to decommissioning and are carried through to site release. The standard recommends a dose constraint for the released site of less than 300 microsieverts per year and a limit below which further dose reduction measures are unlikely to be warranted of approximately 10 microsieverts per year. The zone between 10 and 300 microsieverts per year is considered to be a zone of optimization for both restricted and unre­stricted land release.

The IAEA approach provides both for cases where the release is without restrictions and for cases where the future uses of the land remain under some form of use restrictions. In the restricted case, it is possible to carry out prospective effective dose assessments with assumptions that certain sources remain under control and hence a greater degree of residual con­tamination can remain in situ. The standard recommends that should such controls fail, the effective dose should not exceed 1 millisievert per year.

The IAEA standard describes a generic approach to site release and licence termination which is expanded upon and developed within this chapter as a whole. The dose criteria for release are developed through evaluation of potential radiological consequences through all relevant exposure pathways into radionuclide release criteria (Becquerels per gram). These can be determined generically and set by the regulatory body or be developed on a case-by-case basis. Generic criteria may be more conserva­tive because of the need to make generic assumptions in the dose assess­ment. The released site should be assessed for a variety of exposure scenarios including those in which material from the site is reused or circulated outside of regulatory control. The assessment should take into account uncertainties such as those arising from sampling and analysis.

The standard describes the roles of the national government, the regula­tory body and the operator in site release and licence termination. The national government should establish a legal framework under which ter­mination of practices can occur. The regulatory body should establish detailed criteria and associated guidance, review submissions for site release, perform inspections, take actions if required and issue the licence termina­tion once due process has been completed. The operator is responsible for safe completion of decommissioning, remediation, clean-up and licence termination processes under a specific management system. The management system should cover a process for licence termination, respon­sibilities, competency, calibration and maintenance of survey equipment, quality assurance, record keeping, independent assessment/auditing and non-conformance.

As an example of national approaches, the UK regulatory approach is given in the following. In the UK, licence termination is referred to as ‘de­licensing’. Major nuclear facilities are licensed under the Nuclear Installa­tions Act 1965. Prior to 2005 several examples of de-licensing occurred on parts of UK nuclear sites and for some small research facilities. In 2005, with progress towards large-scale decommissioning in the UK, the Health and Safety Executive (HSE), as the principal regulator, issued formal cri­teria for de-licensing (HSE, 2005). The main features are: [24]

the risk criterion. Where these generic values are not used, a specific case-by-case risk assessment may be submitted by the operator.

• Where practicable, sources of ionizing radiation (e. g., a radiographic source) should not be within the de-licensing area at the time of de­licensing (but may be returned later where this does not require a nuclear licence). Materials which could be defined as radioactive waste (RAW) under UK legislation should not be present on the site.

The UK de-licensing regime follows the main features of the generic inter­national arrangements suggested by the IAEA. The UK uses the lower of the range of optimization suggested by the IAEA for unrestricted use and has no arrangements for licence termination under restricted uses. Several significant parts of nuclear sites have been de-licensed using these criteria since 2005.

It is often the case that regulatory authorities take a conservative approach to release of areas after termination of practices because the decision rep­resents a point at which formal control is relinquished. In many cases the most conservative dose criteria are used and the assessments are based upon very extensive site investigation. In the UK, for example, a 1 in a million per year risk target is used to achieve unrestricted release. For some sites with complex and extensive histories, it may not be practicable to achieve such rigorous criteria without tremendously costly clean-up and very large waste production. For these sites the concept of restricted reuse under ongoing regulatory controls less onerous than full licensing as required for the original practice should be an approach more widely employed. This may require in-situ waste ‘disposal’ authorizations or other forms of institutional control. The restricted release approach may be par­ticularly applicable where the next use of the land is for industrial or new nuclear uses for which the potential for public exposure is limited.

If a pragmatic approach to release after termination of practices is not taken by all parties, there is potential for a ‘greenfield’ approach in which all physical assets are removed and the site returned to an essentially virgin state in order to enable release. In many cases it will be more appropriate to recognize the value of existing buildings, assets and infrastructure and attempt to retain these through the termination process for economic reuse.