2.1. A CHANGE IN PARADIGMS
In recent years a slow change in paradigms has occurred: awakening awareness of long term ecological problems has led to a move away from treating environmental problems only after they have occurred. The goal is to avoid environmental impacts from the beginning in the life cycle of a human activity. This life cycle management aims to treat each stage in the life of a facility or site not as an isolated event but as one phase in its overall life. Thus,
the planning does not only cover each stage but is also a continuing activity, taking into account actual and projected developments.
As a consequence, a more forward looking integrated management of human activities was introduced into the legislation in many Member States.
2.2. DEFINITIONS OF STEWARDSHIP
The long term and life cycle management of radiological liabilities requires certain provisions and institutions. In recent years the term stewardship has been coined to describe the various activities associated with the long term management of sites with radiological liabilities [3, 4]. In general,
‘long term stewardship’ indicates the technical, societal and management measures needed to ensure the long term protection of humans and the environment at sites characterized by residual hazards after active remediation or assessment has been completed.
Different audiences have used the term ‘long term stewardship’ with different meanings. According to the Oxford English Dictionary, a steward is a person entrusted with the management of another’s property. In this sense, stewardship in the present context means taking care of sites or land with radioactivity in the ground. More specifically, it refers to those instances or phases of such sites, where, for instance, active remediation has been completed, but residual radioactivity is left, not allowing the free release of the site or land. Accordingly, the United States Department of Energy (USDOE) defines stewardship as:
“the physical controls, institutions, information and other mechanisms needed to ensure protection of people and the environment at sites where DOE has completed or plans to complete ‘cleanup’ (e.g. landfill closures, remedial actions, removal actions, and facility stabilization). This concept of long-term stewardship includes, inter alia, land-use controls, monitoring, maintenance and information management” (see Refs [5, 6]).
There are several challenges, both technical and institutional, associated with long term stewardship. A recent report by the National Research Council of the United States National Academies defined the roles of a long term steward of a site with long lived hazards as [7]:
— A guardian, stopping activities that could be dangerous;
— A watchman for problems as they arise, via monitoring that is effective in design and practice, activating responses and notifying responsible parties as needed;
— A land manager, facilitating ecological processes and human use;
— A repairer of engineered and ecological structures as failures occur and are discovered, as unexpected problems are found, and as re-remediation is needed;
— An archivist of knowledge and data, to inform future generations;
— An educator to affected communities, renewing memory of the site’s history, hazards and burdens;
— A trustee, assuring the financial resources to accomplish all of the other functions.
Nevertheless, it would always be the objective of life cycle management to minimize the need for stewardship within an overall optimizing management approach.
2.3. WHEN DOES LONG TERM STEWARDSHIP BEGIN?
Figure 2 shows the generic life cycle of a nuclear facility. The early stages of the life cycle consist of identifying the need for an activity site and selecting the site as well as designing, constructing and operating the nuclear facility.
At the end of the operational phase, the site undergoes decommissioning and active remediation. Decommissioning involves actions such as decontami-nation, demolition and dismantling of buildings and equipment, and waste conditioning. During active remediation, engineered, physical and chemical measures (e.g. caps, liners, reactive barriers and microorganisms) are put into place to protect human health and the environment. In some countries, decom-missioning and active remediation are considered as an integrated process. In these countries, the boundary between decommissioning and the onset of site remediation is blurred, and there might be different cycles of decommissioning and site remediation. In some countries, these cycles may last for decades to allow the decay of short lived radioactivity and this process is called ‘safestore’.
Need
of needs SitingSiting Designing,
construction OperationOperation
FIG. 2. Life cycle management.
In these cases, there may be interim ‘fit for purpose’ land uses at the end of each cycle. In contrast, in other countries, decommissioning is completed before site remediation begins, so that the boundaries are clearly defined. A site may also be split into sub-sites that are fit for free release and others that require institutional control. A suitable split may greatly facilitate a subsequent stewardship programme [8].
Long term stewardship begins after the end of decommissioning and active remediation. The intermediate guarantee phase of several years that is sometimes imposed for engineered structures, etc., might be viewed as part of the active phase or already be part of the stewardship phase. Long term stewardship fundamentally does not encompass any active remediation.
Hazards on the site will have been removed or been contained by engineered systems put into place during the active remediation phase, or natural processes, such as attenuation, dispersion or radioactive decay, will have been used to keep exposures below levels of concern. Long term stewardship primarily involves the care and maintenance of the site and any structures built as part of the remediation solution. Monitoring activities ensure that the remediation solution behaves as predicted and that any land use restrictions are complied with. In some cases, a permanent solution may have been deferred until a (more) suitable remediation technology has been developed, and the site has been put into a stewardship-like state in the interim period.
A long term stewardship programme is being developed during the active remediation and decommissioning phase, and addresses monitoring and maintenance as well as including provisions for corrective actions in case of deviation from the predicted behaviour of the site. The final end state is ideally the unrestricted release of the site. However, if any control measures remain necessary, long term stewardship needs to be put into place. If unrestricted release is not possible, the site can still be used for specific purposes (e.g.
industrial use) but the steward needs to ensure that the restrictions are complied with.
2.4. WHEN DOES LONG TERM STEWARDSHIP END?
The length of the long term stewardship phase depends on the half-lives of the residual radionuclides of concern. For some sites, where relatively short lived radionuclides such as 137Cs and 90Sr are the problem, the period of stewardship can be of the order of hundreds of years. Where long lived radio-nuclides, such as many of the isotopes of uranium, thorium and plutonium, are the problem, the stewardship period may have to last effectively for ever.
It can be noted that these considerations also become more and more important and receive increasing public attention in the case of ‘conventional contaminants’ such as heavy metals, persistent organic pollutants and other toxic or hazardous substances.
The term ‘long term’ is interpreted differently in different Member States.
Administrations in various Member States have adopted for practical reasons certain time spans; thus a 1000 year basis may have been selected for engineering designs in this context.