How potential exposures may be incorporated in IAEA Safety Standards

Transcription

1 How potential exposures may be incorporated in Safety Standards Diego Telleria NSRW- Meeting of INPRO ENV POTENTIAL CIEMAT, Madrid, April 2014 International Atomic Energy Agency

2 REQUIREMENTS FOR ASSESSMENT AND CONTROL OF POTENTIAL EXPOSURE Paragraph 3.24 of the BSS establishes that: registrants and licensees shall ensure that all relevant factors are taken into account in a coherent way in the optimization of protection and safety to contribute to achieving the following objectives: To determine measures for protection and safety that are optimized for the prevailing circumstances, with account taken of the available options for protection and safety as well as the nature, likelihood and magnitude of exposures; To establish criteria, on the basis of the results of the optimization, for the restriction of the likelihood and magnitudes of exposures by means of measures for preventing accidents and for mitigating the consequences of those that do occur.

3 REQUIREMENTS FOR ASSESSMENT AND CONTROL OF POTENTIAL EXPOSURE Paragraph 3.15 of the BSS establishes that : Registrants and licensees shall assess the likelihood and magnitude of potential exposures, their likely consequences and the number of persons who may be affected by them. Requirement 6 of GSR Part 4 states that : the possible radiation risks associated with the facility or activity shall be identified and assessed. These include the level and likelihood of radiation exposure of [ ] the public, and of the possible release of radioactive material to the environment, that are associated with anticipated operational occurrences or with accidents that lead to a loss of control over a nuclear reactor core, nuclear chain reaction, radioactive source or any other source of radiation.

4 REQUIREMENTS FOR ASSESSMENT AND CONTROL OF POTENTIAL EXPOSURE Requirement 13 of the BSS states inter alia that: safety assessment shall: Identify the ways in which exposures could be incurred... Determine the expected magnitudes and likelihoods of exposures in normal operations and, to the extent reasonable and practicable, make an assessment of potential exposures.

5 ASSESSMENT OF PROTECTION FOR THE PUBLIC AGAINST POTENTIAL EXPOSURES Facilities are designed, operated and maintained in order to prevent and mitigate incidents that, in the vast majority of cases, result in no radiological consequences for the public. Accidents, with low and very low probability, leading to releases to the environment could occur. In order to assess during the planning phase of a facility the potential exposures to members of the public those accidents, with their probabilities, should be considered.

6 ASSESSMENT OF PROTECTION FOR THE PUBLIC AGAINST POTENTIAL EXPOSURES The consideration of potential exposures in the assessment of facilities may vary between States This is subject to the regulations and guidelines of regulatory bodies. The regulatory body should define the characteristics of the assessments of potential exposures to be used in an authorization processes.

7 Possible accidents to be considered DBA BDBA with no significant releases BDBA with significant releases: Severe Accidents For the purpose of INPRO ENV PE we are evaluating Severe Accidents

8 Types of consequences to be assessed Health effects due to radiation doses to members of the public at the individual level, using the concept of reference person and representative person. Exposures to flora and fauna are not taken into account, since those are not amenable to regulatory control under accidental situations. Postulated severe accidents may also cause social, economic and broader environmental implications, which are beyond the guidance by. Radiological and non-radiological consequences of an emergency are considered in the safety guidance in the framework of emergency preparedness and response.

9 Potential exposure scenarios Selecting a single conservative accident A single conservative accident is an accident specified using what is assumed to be a bounding set of failure conditions that may be recognized as representative of a worst case accidental scenario. This type of assessment is sometimes termed a deterministic assessment ; however, it is clear that the consequences have associated probabilities. Identifying a set of characteristic accidents Characteristic accidents are accidents that, as a result of the safety assessment, can be considered to be a comprehensive representation of the safety characteristics of the facility. The accidents identified as characteristics can be divided into different categories in accordance with their annual frequency or likelihood of occurrence and their consequences. Characteristic accidents do not necessarily include the worst case scenario which tends to be an over-conservative assumption leading to unrealistic potential consequences. Identifying accident sequences from a broad range of initiating events by means of a methodological approach. A methodological approach to identifying accident sequences that can follow from a broad range of initiating events and that include a systematic determination of accident frequencies and consequences is known as probabilistic safety analysis (PSA).

10 Procedure for the assessment FIG. 4. Components of an assessment for potential exposures.

11 Comparison of dose/risk with criteria If, the assessment of potential exposures is based on indications of risk, the nuclear regulatory body should establish a risk constraint; this could be based, for example, on INSAG or ICRP guidance. Another option may be to express the criteria in terms of a consequence to the public that would be unacceptable. Very disruptive countermeasures, like evacuation or relocation, as a result of the potential accident scenarios specified for the facility or activity would not be acceptable. The need of these countermeasures is generally determined using estimations of projected doses (or related operational magnitudes) and comparing these estimations against emergency response decision criteria. If this approach is used, the regulatory body should define the decision criteria for countermeasures to be used for the assessment of the potential exposures

12 International Atomic Energy Agency

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