Office for Nuclear Regulation

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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:

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.

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:

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).

Further information

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.