Assessing dose of the representative person forthe purpose of radiation protection of the public

The Commission intended that its revised recommendations should be based on a

simple, but widely applicable, system of protection that would clarify its objectives and provide

a basis for the more formal systems needed by operating managers and regulators. The

recommendations would establish quantified constraints, or limits, on individual dose from

specified sources. These dose constraints apply to actual or representative people who

encounter occupational, medical, and public exposures. This report updates the previous

guidance for estimating dose to the public. Dose to the public cannot be measured directly

and, in some cases, it cannot be measured at all. Therefore, for the purpose of protection of the

public, it is necessary to characterise an individual, either hypothetical or specific, whose dose

can be used for determining compliance with the relevant dose constraint. This individual is

defined as the 'representative person'. The Commission's goal of protection of the public is

achieved if the relevant dose constraint for this individual for a single source is met and

radiological protection is optimised.

This report explains the process of estimating annual dose and recognises that a number of

different methods are available for this purpose. These methods range from deterministic

calculations to more complex probabilistic techniques. In addition, a mixture of these techniques

may be applied. In selecting characteristics of the representative person, three important

concepts should be borne in mind: reasonableness, sustainability, and homogeneity. Each

concept is explained and examples are provided to illustrate their roles. Doses to the public are

prospective (may occur in the future) or retrospective (occurred in the past). Prospective doses

are for hypothetical individuals who may or may not exist in the future, while retrospective

doses are generally calculated for specific individuals.

The Commission recognises that the level of detail afforded by its provision of dose coefficients

for six age categories is not necessary in making prospective assessments of dose, given

the inherent uncertainties usually associated with estimating dose to the public and with

identification of the representative person. It now recommends the use of three age categories

for estimating annual dose to the representative person for prospective assessments. These

categories are 0-5 years (infant), 6-15 years (child), and 16-70 years (adult). For practical

implementation of this recommendation, dose coefficients and habit data for a 1-year-old

infant, a 10-year-old child, and an adult should be used to represent the three age categories.

In a probabilistic assessment of dose, whether from a planned facility or an existing situation,

the Commission recommends that the representative person should be defined such that

the probability is less than about 5% that a person drawn at random from the population will

receive a greater dose. If such an assessment indicates that a few tens of people or more could

receive doses above the relevant constraint, the characteristics of these people need to be

explored. If, following further analysis, it is shown that doses to a few tens of people are indeed

likely to exceed the relevant dose constraint, actions to modify the exposure should be considered.

The Commission recognises the role that stakeholders can play in identifying characteristics

of the representative person. Involvement of stakeholders can significantly improve the

quality, understanding, and acceptability of the characteristics of the representative person

and the resulting estimated dose.

The optimisation of radiological protection: Broadening the process

The principle of optimisation of radiation protection is defined by the Commission

as the source-related process to keep the magnitude of individual doses, the number of people

exposed, and the likelihood of potential exposure as low as reasonably achievable below the

appropriate dose constraints, with economic and social factors being taken into account.

According to the revised recommendations of ICRP, this process of optimisation below

constraint should be applied whatever the exposure situation; i.e. planned, emergency, and

existing.

The previous recommendations for the practical implementation of the optimisation process

are still valid. It must be implemented through an ongoing, cyclical process that involves the

evaluation of the exposure situation to identify the need for action, the identification of the

possible protective options to keep the exposure as low as reasonably achievable, the selection

of the best option under the prevailing circumstances, the implementation of the selected option

through an effective optimisation programme, and regular review of the exposure situation to

evaluate if the prevailing circumstances call for the implementation of corrective protective

actions. However, the way in which the optimisation process should be implemented is now

viewed more broadly to reflect the increasing role of individual equity, safety culture, and

stakeholder involvement in our modern societies.

This report is a consolidation and an evolution of the Commission's recommendations

concerning the optimisation principle. After some background information on the foundation

and evolution of the principle, this report describes the main characteristics of the process,

addresses the issue of exposure distribution in that process, and provides the basic requirements

for its application in operation and regulation. A description of decision-aiding techniques

commonly used for practical implementation of the optimisation process is provided in

Annex A.