K.1 The hazard

This PNERP details the response to an ionizing radiation hazard, resulting from an accident, malfunction, or loss of control at a reactor facility (i.e., nuclear emergency). The public may be harmed by radiation released from such incidents via the following exposure pathways:

  1. External exposure resulting from:
    1. Radiation emitted by airborne radioactive materials in a plume (“cloudshine”)
    2. Radiation emitted by radioactive materials that have deposited on the ground (“groundshine”)
    3. Radiation emitted by radioactive materials that have deposited on clothing or skin (“external contamination”).
  2. Internal exposure resulting from radioactive materials that entered the body (“internal contamination”) by:
    1. Inhalation of radioactive airborne materials
    2. Skin absorption or wound absorption of radioactive material
    3. Ingestion of drinking water, plant or animal products that have radioactive materials on or in them.

Health effects from exposure to ionizing radiation can be grouped into two main categories:

  1. Stochastic effects are those resulting from chronic low doses of radiation. They present primarily in the form of increased risk of various latent cancer types.
  2. Deterministic effects are those resulting from high doses of radiation and include cell death or tissue reactions.

The likelihood of stochastic and deterministic effects is reduced when protective actions are promptly implemented.

Nuclear and radiological hazards may be measured in both Imperial and System International (SI) units. A unit conversion table is provided in Annex R .

Other potential effects of the hazard, including those on mental health, psychological, psychosocial, environment, education, culture, ethics, political governance, traditional ways of knowing/living, etc. must also be considered in response to decision-making.

K.2 Planning basis for nuclear emergencies

The planning basis involves the identification of hazards that the nuclear emergency management program must address based on the impact on health and safety, property and the environment. In a nuclear emergency, an ionizing radiation hazard could arise from an accident or event at a reactor facility, whereas a radiological emergency is not location dependent.

Elements of the planning basis include:

  1. the radiological hazard(s)
  2. the basis for protective action decision-making, i.e., GC and operational intervention levels (Annex Q)
  3. the potential effects on public health and safety (i.e., potential radiation doses resulting from a) above)
  4. the geographical extent of consequences.

K.3 Reactor Facility Accidents

Nuclear emergency management requires a planning basis which considers both design basis accidents (DBAs) and beyond design basis accidents (BDBAs), including severe accidents and multi-unit scenarios where applicable.

While the planning basis should include a wide range of accidents, the amount of detailed planning should decrease as the probability of the accidents’ occurrence decreases. For this reason, the planning basis for managing a nuclear emergency must strike an appropriate balance.

Reactor facility safety analyses and risk assessments shall be used to inform the planning basis.

This PNERP has been prepared in conformity with national and international standards and guidance for nuclear emergency management and, as such, it:

  1. Provides detailed planning and preparedness to mitigate the effects of DBAs for which safety systems have been specifically designed to ensure that radiological releases are kept within authorized limits
  2. Provides additional tools and mechanisms to mitigate the effects of BDBAs, including severe accidents, which are more unlikely than Design Basis Accidents.

K.3.1 Design Basis Accidents

The DBA release provides the main platform for detailed planning and is generally characterized by one or more of the following:

  1. An accident that a nuclear facility has been specifically designed to withstand
  2. Station containment systems would function normally, allowing radiation to decay prior to a controlled release
  3. Sufficient time would be available to alert the public and implement protective measures prior to a release
  4. The main radiological hazard to people would be external exposure to, and inhalation of, radioactive material
  5. Filter systems would function to remove almost all of the radioiodines and particulate radionuclides. As a result, the plume would be mostly comprised of inert noble gases, which would dissipate and not pose a contamination hazard.
  6. Radiation doses to the public would likely be below the GC as defined in Annex Q
  7. Environmental contamination would be limited to very low levels
  8. The area affected would likely be contained to the Detailed Planning Zone.
  9. Low-level radioactive releases to the environment could occur on and off for some time (e.g., days or weeks).

Planning and preparedness shall be conducted in Ontario to mitigate the consequences of releases from DBAs and shall further provide the basis for an expanded response, as required, to mitigate the effects of a Beyond Design Basis Accident (BDBA).

K.3.2 Beyond Design Basis Accidents

The BDBA is an exceptionally low probability event that is more severe than a DBA and is generally characterized by one or more of the following:

  1. A single unit or multi-unit accident (i.e., an accident involving more than one reactor) that exceeds the conditions a facility has been designed to withstand
  2. Station containment system impairment leading to:
    1. Significantly reduced hold up time of radioactivity in containment resulting in reduced decay of radioactive materials;
    2. Little time available to alert the public and implement protective measures;
    3. An early release of radioactivity; or
    4. An uncontrolled and unfiltered release of radioactivity
  3. The main radiological hazard to people would be external exposure to, and inhalation or ingestion of, released radioactive material
  4. Filter systems may fail, leading to the release of a mix of particulates, radioiodines, and noble gasses
  5. Released radioiodines could be inhaled or ingested leading to internal exposure of the thyroid gland
  6. Radiation doses could potentially be high and could potentially exceed the GC as defined in Annex Q
  7. Environmental contamination could be quantitatively significant in both extent and duration
  8. The area affected could extend beyond the Detailed Planning Zone into the Contingency and Ingestion Planning Zones
  9. Radioactive releases to the environment could occur on and off for some time (e.g., days or weeks).

BDBAs which go unmitigated may evolve into a more severe accident involving fuel degradation in the reactor core.

The response to BDBAs is facilitated by the measures already in place to respond to DBAs and the ability to expand their function.

Additional planning and preparedness measures shall be undertaken to facilitate the implementation of the following response actions, as appropriate, to mitigate the much less probable, but possibly more severe, offsite effects of BDBAs:

  1. Initiation of public alerting to direct protective actions, including sheltering and evacuation
  2. Priority evacuations for those closest to the hazard
  3. Radiation monitoring and, if necessary, decontamination of persons.
  4. Urgent Response Phase Iodine Thyroid Blocking (ITB)
  5. Timely dispatch of aerial and ground monitoring teams to determine areas of contamination
  6. Medical assessment, treatment and counselling as required.