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Catégorie : Communications

Publication : mardi 8 octobre 2013 14:51

LOCHARD, J., SCHNEIDER,T.

Oral presentation at the 2nd International Symposium on ‘The Safety Case for Deep Geological Disposal of Radioactive Waste: 2013 State-of-the-Art’, OECD/NEA, Paris, 8 October 2013

The management of radioactive waste has been the subject of several recommendations of the International Commission on Radiological Protection (ICRP) since 1985. The aim of the new Publication 122 (2013) is to describe how the 2007 general recommendations of th Commission (Publication 103) can be applied in the context of geological disposal. For this purpose, it is important to remind that the new approach developed by ICRP is based on three types of exposure situations: planned, emergency and existing.

• Planned exposure situations correspond to situations where exposures result from the operation of deliberately introduced sources. Exposures can be planned and fully controlled.
• Emergency exposure situations correspond to situations where exposures result from the loss of control of a source within a planned exposure, or from an unexpected situation (e.g. malovelent event). These situations require urgent actions to prevent or mitigate exposures.
• Existing exposure situations correspond to situations where exposures result from sources that already exist when decisions are taken to control them. The characterization of exposure is therefore a prerequisite for their control.

The application of the three basic radiological protection principles - justification, optimization of protection and limitation of individual doses – are therefore considered in this new framework with justification and optimzation applying to the three types of exposure situations and limitation only to planned exposure situations.

The main points highlighted in Publication 122 for the application of the system of radiological protection to geological disposal of long life solid radioactive waste are the following:

• For the protection of the future generations, the Commission's Recommendations are based on the fundamental principle that: "Individuals and populations in the future should be afforded at least the same level of protection as the current generation" (This principle was already in ICRP Publication 81).
• The Commission considers that the potential exposures to humans and the environment associated with the expected geological disposal for long life solid radioactive waste correspond to a planned exposure situation. They are taken into account at the time of the design of the disposal facility and protection strategies have to be developed to cope with these potential exposures.
• The application of the radiological protection system is significantly influenced by the level of oversigth and "watchful care" of the disposal facility. Three major timeframes have to be taken into account for radiation protection purpose:
  • the period of direct oversight during which the disposal facility is operated and is under active supervision;
  • the period of indirect oversight during which the disposal facility is partially or fully sealed and where indirect oversight takes the form of regulatory supervision, administrative and societal oversight;
  • the period of no oversight corresponding to a situation where the memory of the disposal facility has been lost and society is no longer in a position to keep a watchful eye on the facility. It is important to note that the Commission recommends to preserve oversight as long as possible because of its contribution to the overhall effectiveness of protection.
• In this perspective, the various decisions to be made over time regarding the evolution of the monitoring and oversight should be discussed with stakeholders.
• Even when the memory of the disposal facility has been lost, leading to the abandonment of all forms of monitoring of the facility, the intrisic functions of the repository still exist. The potential to retain and isolate the radioactive waste is an inherent feature of the repository and it continues into the distant future. This leads to address potential exposures as a planned exposure situation, except in the case of major disruptive events.
• For the application of the principle of justification, waste management and disposal operations have to be considered as an integral part of the practice generating the waste. In addition, it is recommended to review this justification over the life time of that practice whenever significant new information or event might call into question the justification.
• The optimization of protection is the central element for the implementation of the system of radiological protection in the case of a geological disposal facility. This approach, based on a stepwise process during the various stages of disposal (design, operation, monitoring) should enable the systematic and transparent assessment of protection options, including considerations on the best available techniques. The objective of the application of the optimization principle is to strengthen the capacity of storage protection and reduce potential impacts (radiological and others).
• In accordance with the optimization principle, the radiological criterion recommended by the ICRP for the design of a disposal facility is an annual dose constraint for the population of 0.3 mSv per year and a dose constraint bellow the annual dose limit of 20 mSv per year or 100 mSv over 5 years for occupationally exposed workers.
• A risk constraint for the population of 1 10-5 per year is also recommended when applying an aggregated approach combining the likelihood of the exposure scenario and the associated dose.
• It is recalled that the dose assessments and risk over the long term should be used for the comparison of options rather than a means of assessing health detriment.
• For natural events considered in the design of the disposal, the Commission recommends choosing dose or risk constraints in the band used for planned exposure situations.
• For severe natural disruptive events not taken into account in the design-basis evolution as well as for the inadvertent human intrusion, the dose or risk constraint does not apply. In that case, if the events were to occur during the period of direct or indirect oversight of the disposal facility, then the competent authority should take appropriate measures with reference to the emergency and / or existing exposure situations.
• The implementation of the recommendations of the Commission requires a management system that integrates safety, health, environment, security, quality and economic considerations, stressing that safety remains the fundamental objective. The system has to support a transparent approach involving all relevant stakeholders.
• For the protection of the environment, in the absence of detailed assessment and corresponding criteria, evaluations in this area have to be addressed with a view to inform decision making.

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