ONR principles for determination of offsite emergency planning areas (formerly known as DEPZs)
In January 2014, ONR published revised principles for determining detailed emergency planning zones (DEPZs) around nuclear sites in the UK. These principles mean that ONR will look beyond the technical assessment of the hazards on site and also consider local practical and geographical issues in the operation of the off-site plan.
What is a detailed emergency planning zone?
This is the area around a facility for which the Radiation (Emergency Preparedness and Public Information) Regulations 2001 (REPPIR) requires the local authority to prepare a detailed off-site emergency plan with the purpose of restricting, so far as is reasonably practicable, public exposure in the event of a reasonably foreseeable radiation emergency.
A radiation emergency is defined in REPPIR as any event likely to result in any member of the public being exposed to ionising radiations in excess of any of the dose levels set out in Schedule 1 in the Regulations usually described as 5 mSv over the year immediately following a radiation emergency
The off-site emergency plan describes arrangements to prevent or restrict radiation exposure of both the public and emergency workers in the zone. It includes, for example, advice on aid and countermeasures such as sheltering, evacuation and, in the case of operational reactor sites, the administration of stable potassium iodate tablets.
Local authorities are responsible for the development, consultation and implementation of the emergency plan.
Who determines the extent of DEPZs?
REPPIR 2001 Regulation 9(1) places the duty to determine DEPZs on the Health and Safety Executive amended by the Energy Act 2013 to the Office for Nuclear Regulation (ONR) for nuclear facilities.
What is the process for setting a DEPZ?
In order to provide a consistent approach to the determination of DEPZs, ONR applies a defined regulatory process and clear principles. These are contained in the following two-step approach:
- The undertaking of an assessment, by ONR, of the nuclear site operators' technical report relating to the area in which members of the public or emergency workers are likely to be affected by a radiation emergency, as defined in REPPIR.
- Consideration of practical and strategic factors related to the implementation of the offsite emergency plan and confidence in public protection. This will involve dialogue with the relevant local authority on matters such as local demographics and geography.
Balancing the assessment of the technical report with practical and strategic considerations enables ONR's determination of the DEPZ to reflect specific local circumstances.
What does the technical assessment involve?
REPPIR requires a number of steps to be followed to reach a determination of the area where workers or the public could be affected by a radiological emergency.
- Firstly REPPIR requires the operator of a nuclear facility, to undertake Hazard Identification and Risk Evaluation (HIRE) which considers all hazards on the site that have the potential to cause a radiation accident; from small occurrences to radiation emergencies. The evaluation should include possible plant and equipment failures, breakdown of administrative arrangements and potential unauthorised behaviour of employees or the public. The HIRE will show whether there is a potential for a reasonably foreseeable radiation emergency.
- The operator is required to review the HIRE every three years or upon a material change e.g. use of different radioactive substances or different quantities of the same substances, or the use of new or different technologies.
- The operator then has to submit the outcome of this review to ONR in the form of a Report of Assessment (RoA).
- In the RoA the operator will identify a radiological footprint or zone that it believes corresponds to doses to members of the public from a reasonably foreseeable radiation emergency that relate to the dose thresholds in Schedule 1 of REPPIR.
- ONR's makes a technical assessment of the content and accuracy of the RoA, and, if necessary, will request further details to determine whether it agrees, or otherwise, with the operators technical footprint or zone.
- Once satisfied ONR produces an internal report that verifies that the operator has fulfilled their REPPIR requirements, adequately assessed all of the relevant hazards, and provided a reasonable estimate of the radiological footprint and contour within which members of the public are likely to receive radiation exposures greater than 5 mSv.
This is used to inform, not prescribe, the final extent of the DEPZ.
ONR then considers how this 5 mSv contour might be modified by consideration of other relevant practical and strategic factors in order to determine the DEPZ.
What practical and strategic factors do ONR consider?
In addition to the area identified by the technical assessment, the following practical and strategic factors are also considered by ONR to be relevant in determining the extent of the DEPZ:
- Local geographic, demographic and practical implementation factors - The relevant local authority is consulted as it has significant local knowledge and is responsible for developing and implementing the off-site emergency plan in the unlikely event of an incident.
- Avoidance of bisecting local communities - Although it may sometimes be unavoidable, ONR seeks to avoid the bisection of small communities as this may affect the effective delivery of countermeasures.
- Inclusion of immediately adjacent vulnerable groups - ONR recognises that groups of vulnerable people (e.g. care homes, schools, camping sites, etc) located adjacent but outside a DEPZ should be provided for in the same manner as those located within the zone.
- International standards and guidance - ONR is of the view that its decisions should be informed by accepted international good practice.
- Credibility and confidence in the extent of the DEPZ - Although REPPIR places the duty on ONR to make an objective and unbiased regulatory determination of the extent of the DEPZ, ONR considers that the DEPZ should be of sufficient size to provide a meaningful off-site emergency plan. It should therefore incorporate an appropriate degree of conservatism to engender public confidence and provide for a credible and effective response in the event of a reasonably foreseeable radiation emergency.
- Benefits and disbenefits of countermeasures Countermeasures, such as evacuation, can carry a risk so ONR considers that the DEPZ should represent an appropriate balance between securing the benefits of dose aversion and the potential disbenefits associated with implementing immediate countermeasures in a radiation emergency.
- Other site specific factors of which ONR is aware - ONR will also consider any additional site-specific factors that it considers relevant on a case-by-case basis.
Upon completion of the DEPZ determination process, ONR produces and publishes on our website a Project Assessment Report that details the basis for our determination of the DEPZ in question, and also sets out a description or map of the geographical area concerned.
How is a DEPZ implemented?
The DEPZ is implemented by a formal letter from ONR to the relevant local authority notifying it of the extent of the DEPZ and of the need to prepare or update their off-site emergency plan within a period of six months (or longer if HSE agree). Copies of these letters are also sent to the relevant operator(s).
For more information on how ONR undertakes technical assessments of licensees HIRE/RoA see ONR's Nuclear Safety Technical Assessment Guide, The Technical Assessment of REPPIR Submissions (NS-TAST-GD-082, Revision 2). This provides advice to ONR inspectors/assessors to assist consistency in their judgements as to whether an operator has, or has not, met the requirements of REPPIR. It also provides guidance in relation to whether a radiation emergency is considered reasonably foreseeable.