Introduction

Justification and optimization are important processes in both the development and implementation of the protection strategy. In the context of an emergency or existing exposure situation, these terms are defined in GSR Part 3 [1] and GSR Part 7 [2] as follows:

− Justification is “the process of determining … whether a proposed protective action or remedial action is likely, overall, to be beneficial; i.e. whether the expected benefits to individuals and to society (including the reduction in radiation detriment) from introducing or continuing the protective action or remedial action outweigh the cost of such action and any harm or damage caused by the action.” [1, 2].

− Optimization (of protection and safety) is “the process of determining what level of protection and safety would result in the magnitude of individual doses, the number of individuals (workers and members of the public) subject to exposure and the likelihood of exposure being as low as reasonably achievable, economic and social factors being taken into account (ALARA).” [2].

The process of justification is thus applied in deciding whether actions taken to reduce exposures are likely to do more good than harm, taking account of both the disadvantages (e.g. disruption) and the advantages (e.g. reduction in radiation risk) associated with their implementation. Optimization is then applied to justified actions to ensure that the best is achieved, under the prevailing (or assumed) circumstances, taking account of economic and social factors associated with different means of implementing the justified actions. In other words, while justification and optimization both involve taking account of the costs (or harm) and benefits associated with implementing actions, justification requires that a net benefit is achieved, while optimization further requires that the various components of cost and benefit are balanced to achieve the best (or optimum) result, which may not necessarily be the one with the lowest dose.

As mentioned in Section 2, the concept of the protection strategy, comprising a suite of justified and optimized protective actions and other response actions, has evolved from the previously recommended approach, outlined in GS-R-2 [5] and based on ICRP Publications No. 60 [6] and 63 [7], in which interventions (i.e. individual protective actions) were individually justified and optimized on the basis of the dose that is avertable by that action, using the concept of intervention levels. In GSR Part 7 [2], taking into account the recommendations in ICRP Publication No. 103 [10], the focus for justification and

optimization has been modified to encompass not only individual protective actions but the overall protection strategy as well. Namely, justification has to be applied for individual protective actions themselves as well as to the overall protection strategy (i.e. the combination of protective actions) with the aim to ensure that the net benefit when combining individual actions is not compromised. Justified actions and justified combinations of actions then need to be optimized and incorporated within a protection strategy. Depending on the relation among various actions considered, optimization may to some extent be possible for some protective actions in isolation from other actions considered in the strategy, while in other cases it has to be ensured that all actions in combination would result in the best outcome.

Justification and optimization are complex processes that involve taking account of a range of considerations that call for inputs from various organizations or bodies. They therefore require close collaboration among all the organizations with relevant responsibilities (including operators, regulators and response organizations at different levels) that may own knowledge, information or data on various aspects to be considered in these processes. Examples of the factors that need to be taken into account in the processes of justification and optimization are presented in Annex II to provide, among other things, a basis for identifying the organizations and interested parties that need to be involved in providing relevant inputs to support making an educated guess regarding the justified and optimized actions to be considered.

During the preparedness stage, the justification and optimization processes are applied to develop a protection strategy for a range of postulated emergencies, resulting in a range of potential consequences. This is a generic process, associated with significant uncertainties, for example, in estimating the impact of an emergency. However, during the emergency response, the justification and optimization processes are applied in an actual emergency. In the urgent response phase, priority needs to be given to the implementation of a pre-planned set of justified and optimized precautionary and urgent protective actions. When the emergency progresses into the later phases, there is less urgency associated with implementation of effective emergency response actions and an increasing amount of information becomes available regarding the emergency and its impact. Only at this time, it is possible and reasonable to review how effective the response by that time is, and to explore through thorough justification and optimization processes what else can be done.

The process of evaluation, justification and optimization within the overall process of developing and implementing the protection strategy is illustrated in Fig. 6.

FIG. 6. Illustration of the process of justification and optimization in developing and implementing the protection strategy.

Figure 6 also illustrates the stages at which it is necessary to obtain information from various organizations to make informed decisions. Step 1 was described in Section 3. The present Section provides practical guidance on undertaking Steps 2 to 5 of this process. The factors and considerations presented in Annex I have been expanded in the form of questions and considerations related to the processes of justification and optimization in Tables 3 and 4, referred to in Fig. 6 and elaborated in details in the relevant Sections below.

Figure 7 presents the process of justification and optimization in a simplified way, highlighting its forward looking and iterative features for examining available options for protection and safety and for adjusting the actions to obtain the best outcome.

FIG. 7. Iterative process of justification and optimization of protection and safety in a nuclear or radiological emergency.

The processes of justification and optimization at the preparedness phase and during response are explained in further details in Sections 5.2 to 5.4.