RPS G-2 - The Australian context

GSR Part 3 requires that when an existing exposure situation is identified, responsibilities for protection and safety are assigned and appropriate reference levels are established. Reference levels are used for optimisation of protection in existing exposure situations. For occupational exposure and public exposure in existing exposure situations, a reference level serves as a boundary condition in identifying the range of options for the purpose of optimisation in implementing protective actions. The reference level represents the level of dose or the level of risk above which it is judged to be inappropriate to plan to allow exposures to occur, and below which the optimisation of protection and safety is implemented.

GSR Part 3 requires that the reference level is set in the range of 1-20 mSv effective dose per year. The actual value chosen for the reference level will depend on the prevailing circumstances for the exposures under consideration. The optimised protection strategies are intended to keep doses below the reference level. When an existing exposure situation has been identified, actual exposures could be above or below the reference level. The reference level is used as a benchmark for judging whether further protective actions are necessary and, if so, in prioritising their application.

The main factors to be considered for setting reference levels for existing exposure situations are the feasibility of controlling the situation, and past experience with the management of similar situations. In most existing exposure situations, there is a desire from the exposed individual, as well as from the authorities, to reduce exposures to levels that are close to or similar to situations considered as ‘normal’. This applies particularly in situations of exposures from material resulting from human actions, such as NORM residues and contamination from accidents (ICRP 2007). While an endpoint for the optimisation process should not be fixed, the optimised level of protection will depend on the situation. It is possible to establish intermediate reference levels (see Figure 4.1) that provide a starting point for the optimisation process.

For existing exposure situations involving environmental contamination of a nature that may affect non-human biota, an initial assessment should be conducted to characterise the existing radiological conditions for the contaminated area, including baseline background data. This should include identifying the sources and pathways of exposure for key receptor organisms, estimating the dose rates to those organisms, and comparing with relevant environmental benchmarks as outlined in RPS G-1 (ARPANSA 2015).

When a decision is made not to take protective actions, ongoing review of the situation may be required since future circumstances of exposure may change and evolve over time.

When considering remedial actions in a certain area (e.g. location) the optimisation of protection of humans should take into account and be balanced with the impact of non-human biota in other areas, for example, relocation of waste (ICRP 2014). Considerations should be given when the protection of humans may result in irreversible impacts to the environment (such as when large removal of soil is considered). Optimisation for the protection of non-human biota (which considers populations and not individuals) is not necessarily the reduction of exposures to the most exposed individuals, but could be the reduction of the size of the area affected or the reduction of the number of individuals exposed. A proper balance should be reached to ensure more good than harm, when considering both optimisation for the protection of the public and non-human biota.

A decision should then be made as to what management or intervening action may be required, taking full account of the costs and benefits of the action. The outcome of the initial assessment should help guide the decision-making process.

Verification of the effectiveness of specific protective and remedial actions is important throughout the remediation process. This involves comparison of the actual radiological exposures against the initial estimates, and the measures established for their control. Employers should ensure that the exposure of workers undertaking remedial actions is controlled in accordance with the relevant clauses of occupational exposure in planned exposure situations as stated in the Code for Radiation Protection in Planned Exposure Situations, RPS C-1 (ARPANSA 2016). If the actual exposures significantly differ from the initial estimates, the plan should be revised to account for the actual conditions being experienced. In cases where the actual exposures exceed those predicted, an investigation should be undertaken to improve understanding of the situation, and to prevent actual doses that are higher than anticipated.

Authorities, taking into account the prevailing circumstances, may take advantage of the timing of the overall remediation program to adopt intermediate reference levels to improve the situation progressively (ICRP 2009). In cases of severe contamination, or lack of resources to comply with a full remediation program, it may be considered advantageous to select an intermediate reference level and then, in the light of experience and resource availability, revise the reference level. Intermediate reference levels can facilitate timely decision-making on remediation strategies and the effective deployment of resources. However, when establishing intermediate reference levels, consideration should again be given to the principles of justification and optimisation.

When selecting from a number of options, the decision about appropriate protective measures should be made on the basis of projected doses. These doses can inform the decision regarding appropriate reference levels, such that:

• if projected doses are above 20 mSv y^-1, protective actions are almost always justified
• if doses are below 1 mSv y^-1, protective actions are unlikely to be justified
• if the dose is between those two values, several factors could be considered, as illustrated in Figure 4.1.

If, during the course of remediation, unexpected radiation levels are detected, appropriate measures must be taken to ensure health and safety of workers. Once the new conditions are understood, it may be necessary to revise the site-specific remedial action plan accordingly, and obtain approval from the relevant regulatory body to the restart remediation activities.

The involvement of interested stakeholders should be implemented as early as practicable and needs to be tailored to the nature of the situation, as well as the stage of implementing protective measures. The involvement should allow the public to be included in the decision process (determining strategy, protective measures, etc.) in an active way. This process should begin as early as possible. Communication and information alone are not enough to make people confident in the decisions being made. It should be recognised that the type of engagement, the roles of different stakeholders, and any communication strategy should be established as soon as possible and could vary over the course of implementation of the protection strategy.

Figure 4.1:  Key factors informing the selection of the reference level.

4.1 Remediation of legacy and post-accident sites

Remediation of contamination from past activities or accidents requires the establishment of a reference level in the range 1-20 mSv y^-1 to guide optimisation of radiation protection. The overall remediation process involves four main activities: (1) initial site characterisation and selection of remediation criteria; (2) identification of remediation options and their optimisation, followed by subsequent development and approval of the remediation plan; (3) implementation of the remediation plan; and (4) post-remediation management (IAEA 2007).

In Australia, reasonably foreseeable exposure scenarios are such that it can be considered appropriate to set a site-specific reference level for remediation of contamination from past activities or accidents between 1 and 20 mSv effective dose per year. In the Australian context, an intermediate reference level for remediation of 10 mSv y^-1 is appropriate as a starting point. The actual value will depend on prevailing circumstances and will guide the optimisation of radiation protection. The reference level for remediation applies to additional exposure (i.e. exposure above natural background levels). For undertaking the remediation of an existing exposure situation, occupational and public radiation dose limits apply to the remediation process and should take into account the relevant clauses of planned exposure situations as described in the Code for Radiation Protection in Planned Exposure Situations, RPS C-1 (ARPANSA 2016).

4.2 Radon exposure in homes and workplaces

Within the system of radiological protection, radon exposure has the characteristics of an existing exposure situation as the source is unmodified concentrations of ubiquitous primordial natural activity in the Earth’s crust (ICRP 2007). Human activities such as construction of buildings, operation of mines or underground show caves (ARL 1996) may create or modify pathways that increase exposure to radon and its progeny. These pathways can be controlled by preventative and mitigating actions. The ICRP Publication 126 (ICRP 2015) considers that, in most situations, a national radon protection strategy would be justified as radon is ubiquitous; it represents a significant source of radiation exposure in certain locations and, in many circumstances, it can be controlled..

For implementing protective measures to control radon in dwellings and mixed-use buildings, Australian guidance (ARL 1990) has been based on a derived reference level of 200 Bq m^-3 averaged over a year.

In most workplaces, radon exposures of workers, that are not a result of their assigned or regular work activities are considered adventitious and are not considered to be occupational exposures. The ICRP in Publication 126 (ICRP 2015) recommends a specific graded approach in workplaces with the following steps:

• reducing the concentration of radon to a level that is as low as reasonably achievable, taking into account economic and societal factors, to the same derived reference level established for dwellings and multi-use buildings
• if difficulties are met in reducing levels, optimising protection is recommended using the actual parameters of the exposure situation, such as occupancy and other site specific factors, together with a derived reference level of 1000 Bq m^-3 averaged over a year.

For exposures in workplaces that persist above the derived reference level of 1000 Bq m^-3 averaged over a year, workers should be considered as occupationally exposed. In such cases, the application of the relevant clauses for occupational exposure in planned exposure situations described in the Code for Radiation Protection in Planned Exposure Situations, RPS C-1 (ARPANSA 2016) apply.

The relationship between a measured radon concentration and effective dose depends upon several parameters including the equilibrium factor and the time of exposure, which can vary greatly between locations. However, the Australian values of derived reference level for radon is consistent with the reference level of 10 mSv y^-1 (ICRP 2015) and provides an appropriate level of protection for the public and workers for exposure to radon in homes and workplaces in Australia. These derived reference levels are listed in Annex A of this Guide.

4.3 Aircrew exposure to cosmic rays

Aircrew are exposed to elevated levels of cosmic radiation while flying at high altitude. In Australia, it is expected that an assessment of exposure for aircrew of all domestic and long-haul crews would be warranted. The ICRP, in Publication 132 (ICRP 2016), recommends that a reference level in the 5-10 mSv y^-1 range is selected by employers. The selected reference value is not a dose limit, but represents the level of dose below which exposure should be maintained and reduced as low as reasonably achievable, taking into account economic and societal factors. For Australia, a reference level of 6 mSv y^-1 (see Annex A), is considered appropriate. Where the doses of aircrew are likely to exceed this reference level, and it is not possible to reduce exposure below this reference level, then the relevant clauses for occupational exposure in planned exposure situations as described in the Code for Radiation Protection in Planned Exposure Situations, RPS C-1 (ARPANSA 2016) apply.

For pregnant aircrew, additional protection of the embryo/foetus must be considered. The working conditions of a pregnant worker, after declaration of pregnancy, must ensure that the additional dose to the embryo/foetus would not exceed about 1 mSv y^-1 during the remainder of the pregnancy. If a reference level is in use by employers, dose records or other pertinent assessment are to be kept to enable the optimisation of the reference level.

Radiation doses from cosmic radiation received by occasional flyers is sufficiently low that there is no need to warrant the introduction of protection measures. However, the ICRP recommends that general information about cosmic radiation associated with aviation be available for all passengers (ICRP 2016). Frequent flyers are considered as public exposure and are treated in the same way as occasional flyers (ICRP 2016).

The ICRP, in Publication 132 (ICRP 2016), recommends that, frequent flyers who have exposures comparable to aircrew should be managed as occupationally exposed on a case-by-case basis according to prevailing circumstances. This may result in individuals assessing their own exposure using freely available dose calculators in order to be aware of their exposure and adapt their flight frequency if they feel the need and therefore use this information to engage with their employer, if appropriate.

4.4 Radionuclides of natural origin in commodities and bulk materials

Radionuclides of natural origin occur in commodities including food, animal feed, drinking water, agricultural fertiliser and soil amendments (e.g. additives or pH adjustments), construction materials, and residual radioactive material in the environment. In the context of public exposure in existing exposure situations, all exposure pathways from a given source of exposure need to be considered, including the contributions from external exposure, inhalation and ingestion. A representative person can be exposed to multiple pathways from radionuclides of natural origin in commodities. Therefore, a reference level of 1 mSv y^-1 for exposure to radionuclides in each of the commodities (see clauses 3.2.16-3.2.17 and Annex A of this Guide) is considered appropriate for Australia. For existing exposure situations with dose implications exceeding 1 mSv y^-1, a protection strategy should be developed by the employers in conjunction with the relevant regulatory body and implemented to ensure that any remedial action is justified, and to optimise protection and safety, as described in Section 3 of this Guide.

Food and drinking water

For radionuclides of natural origin in food, or contamination of food arising from radiation practices or accident, assessments are based on a reference level of 1 mSv y^-1 for members of the public.

For importing foodstuffs after a major radiological or nuclear emergency has occurred, the Codex Alimentarius International Food Standards guideline levels are applied for one year after the accident (FAO/WHO 2016). The Codex provides guidance levels for specific radionuclides which are consistent with a reference level of 1 mSv y^-1. ARPANSA assessed that the Codex guideline levels were still sufficient  beyond one year to ensure that the radiation dose due to artificial radionuclides in imported foods would be below 1 mSv y^-1 (ARPANSA 2012).

For radionuclides of natural origin in drinking water or contamination of drinking water arising from past radiation practices that were not subject to regulatory control, the Australian Drinking Water Guidelines (NHMRC 2011) provides a single guideline value (1 mSv y^-1) for the annual exposure to radioactivity from drinking water. The guidelines also provide a process for assessing the radiological quality of the water, including a simple screening method to ensure compliance with the guideline value and an investigation process if the screening levels are exceeded.

When the existing or potential dose from the radionuclide content exceeds the guideline dose, a decision on the need for, and the degree of, remedial action should be based on advice from the relevant state health authorities, and should include a cost-benefit analysis. There may be some circumstances where there is no practical alternative but to accept a dose that exceeds the guideline dose of 1 mSv y^-1, together with a potential slight increase in the risk to health as a consequence. However, if doses from the use of a particular drinking water supply will exceed 10 mSv y^-1, action must be considered to reduce the existing or potential exposures.

Other commodities

The clauses for existing exposure situations in this Guide apply to material containing radionuclides of natural origin at an activity concentration of less than 1 Bq g^-1 for any radionuclide in the ²³⁸U and ²³²Th decay series and of less than 10 Bq g^-1 for ⁴⁰K.

When NORM residues are used as by-products in the form of fertilisers, soil amendments and construction materials (or components of such), the clauses for existing exposure situations apply, irrespective of the activity concentrations. The reasoning behind this is that these everyday commodities, while used in some industrial activities, are also widely used by individual members of the public. Therefore, it would not be appropriate to apply the formal system of regulatory control for practices. In terms of the guidance for existing exposure situations, any restrictions that might need to be placed on these commodities would be imposed by the relevant national regulatory body in the form of simple criteria such as activity concentration limits, in much the same way that levels of other potentially hazardous constituents are controlled.

The use of bulk amounts of materials (e.g. agricultural fertiliser and soil amendments, construction materials, and residual radioactive material in the environment) containing radionuclides of natural origin, should be considered on a case-by-case basis by using a dose criterion of the order of 1 mSv y^-1, commensurate with typical doses due to natural background levels of radiation.

The clauses from the Code for Radiation Protection in Planned Exposure Situations, RPS C-1 (ARPANSA 2016) apply to material containing radionuclides of natural origin where the activity concentration of any radionuclide in the ²³⁸U or ²³²Th decay series exceeds 1 Bq g^-1, or if the activity concentration of ⁴⁰K exceeds 10 Bq g^-1.

4.5 Transition from an emergency exposure situation to an existing exposure situation

The termination of a nuclear or radiological emergency marks the end of the transition phase in a particular area or site and the beginning of either an existing exposure situation or a planned exposure situation (IAEA 2015).

Depending on the nature of the nuclear or radiological emergency, these processes may continue in the longer term after the emergency has been declared terminated. During this period, the implementation of remedial actions might be more efficient than carrying out further disruptive public protective actions.

Transition phase

In addition to the general prerequisites of an emergency exposure situation, the following prerequisites should be met in order to be able to declare the end of an emergency exposure situation and to move to an existing exposure situation:

• justified and optimised actions have been taken to reach the national generic criteria established to enable transitioning to an existing exposure situation, taking into account the criteria in relevant Australian Guides and Standards
• areas have been delineated which may not be inhabited and where it is not feasible to carry out social or economic activity. For these delineated areas, administrative and other provisions have been established to monitor compliance with the restrictions imposed
• a strategy is implemented for the restoration of infrastructure, workplaces and public services necessary to support normal living conditions in the affected areas
• any change or transfer of authority and responsibilities from the emergency response organisation to organisations responsible for the long-term recovery operations have been completed
• communication and consultation is continuous with all interested stakeholders, including local communities
• a long-term monitoring program (e.g. residual contamination) is implemented
• a long-term medical follow-up program for registered individuals, including mental health and psychosocial support for the affected population in relation to psychosocial health consequences is implemented
• administrative arrangements, legislative provisions and regulatory provisions are in place and/or underway for the management of the existing exposure situation.

Termination of an emergency

After terminating the emergency and entering into the existing exposure situation, the reference level for the residual dose in an existing exposure situation should be applied in the band of 1-20 mSv y^-1 as stated in Section 3.2 and Annex A. This Guide recommends that the reference level for the optimisation of the protection strategy is selected from the lower part of the reference band of 1-20 mSv y^-1 as a long-term objective for existing exposure situations (ICRP 2007 and ICRP 2009). Further guidance on selecting reference levels can be found in Figure 4.1.