Existing exposure situations and legacy management

Ted Lazo (NEA) presented.

The ICRP recommends that protection options be justified and optimised and that residual doses should be in the range of those tolerable with protection optimised to ensure residual doses are acceptable. The question is what this means in practice for legacy management

There are a number of different approaches to defining what constitutes a legacy site. Such sites have no identifiable owner and were either operated under historical regulations that do not meet current standards or was never regulated. Since legacy sites already exist, the ICRP suggests they be considered as existing exposure situations, whereby the situation already exists and has generally done so for some time such that it is not possible to control the source, but control of exposure pathways and the exposure of individuals is possible. In managing legacies, the choices made relating to protection need to appropriately address prevailing circumstances; protection options are therefore a site-specific consideration. A framework of tools to optimise radiological protection is provided by the ICRP, but the framework could be considered too rigid.

The ICRP framework aims to support protection decision making in relation to addressing stakeholder concerns and protection of the public, but decisions will vary according to the wider on-gong situation. The prevailing circumstances encompass a broad range of physical,

environmental, social, economic and political issues. Science is needed to support the application of the framework.

In terms of prevailing circumstances for legacies, the situation has generally existed for some time and exposures are normally low to moderate, but could be relatively high. Worker exposures are normally short-term, but may be received over a working lifetime, whereas public exposures are generally chronic and relatively constant over time. The social and economic history of a legacy site can be a very important factor; what is considered intolerable under some circumstances may be tolerable in others. The circumstances of the ICRP exposure situations that drive the tolerability of risk are outlined in Table 21. The optimum solution will depend upon where people are in relation to the legacy site and their protection and other expectations and concerns.

The ICRP frequently refers to tolerability and equity. In planned exposure situations, the tolerability of risk is embodied in the selection of the numerical value of the dose limit and equity is embodied in the selection of the numerical value of the dose constraint. In existing and emergency exposure situations, both tolerability and equity of risk are embodied in the selection of the numerical value of the reference levels.

Optimisation should be framed by the level of risk tolerability associated with the exposure situation. Protection should be implemented such that all exposures are, or are working towards being, as far below the circumstantial tolerability level as reasonably achievable. Optimisation should be applied to meaningfully manage exposure situations in a graded fashion. The choice of dose limits or reference levels and the level of tolerability should be at least partly consider the controllability of the source, the variability of personal exposures, and the importance of personal behaviour in terms of exposure.

Table 21. Circumstances of ICRP exposure situations that drive tolerability of risk.

Exposure

situation Driver

Source Exposure

Planned − Well characterized

− Controllable

− Well regulated

− Well characterized

− Easily manageable

− Public and occupational

management depend on source and pathway control

Existing − Can be characterized

− Largely unchangeable

− Already present

− Can be managed

− Somewhat uncertain

− Public management depends mostly on behavior control

− Graded occupational management Emergency − Very uncertain

− Uncontrollable

− Extremely uncertain

− Hard to manage

− Public and occupational

management is urgently needed and depend mostly on behavior control The prevailing circumstances can have a significant effect on the tolerability of risks and on the identification of an acceptable optimum protection solution. A first and essential step is to listen to and understand stakeholder concerns with regard to the prevailing conditions. The location of sites relative to populations will drive perceptions and culture can play an important role in affecting public viewpoints. Whether dose limits and constraints and/or reference levels are applied should also be driven by the prevailing circumstances, not some preconception.

The key elements of the ICRP system of radiological protection are the application of the principles of justification, optimisation and the application of dose limits (or restriction of dose) according to the exposure situation and the type of exposure (occupational, public or medical). How the framework varies under planned and existing exposure situations is illustrated in Figure 47. Dose constraints do not apply under existing exposure situations. In deciding upon remediation options, dose restriction comes into play. It was suggested however that dose limits rather than dose restriction should be applied for existing situations. For example, where workers are being managed within a planned exposure situation, dose limits are applied, whereas in emergency situations a reference level is applied which may be higher. Activities in both instances are nonetheless planned. The use of a dose limit may therefore be conceptually more appropriate in existing situations where activities for remediation are planned.

In conclusion, there are many different aspects to be taken into account in managing legacy issues.

The management of legacies can be strongly influenced by stakeholder concerns and views, which are themselves strongly influenced by the prevailing conditions. Flexibility is essential to

appropriately managing such situations and an essential first step to legacy management has to be the development of a thorough understanding of all aspects of the prevailing circumstances.

Overall ICRP radiological protection framework

Planned exposure situations

Existing exposure situations

Figure 47. The overall ICRP radiological protection framework (upper figure) and its application to planned (middle) and existing (lower) exposure situations.