3.24.
The siting process, as discussed above, is for the construction and operation of a new nuclear installation at a new site. A similar process should be used for the siting of a new installation at an existing site with certain special considerations. The presence of an existing nuclear installation should not warrant the assumption that the site is suitable for a new nuclear installation. The site evaluation process should be conducted with the same level of rigour as for a new site and it should depend on the implications of the new installation for safety.
3.25.
There are several issues that should be given special attention, such as:
When a site that was selected in the context of an earlier project for a nuclear installation is to be reassessed to confirm that it meets safety requirements;
When a site that had been discarded in the context of an earlier project for a nuclear installation is to be considered for a new project for a nuclear installation.
Such issues include the completion of data, considerations for new regulations and standards, considerations for new methods of analysis and lessons to be learned from recent external events, if relevant.
3.26.
If a new site under consideration is close to or adjacent to the site of an existing nuclear installation, the effects of the existing site on the new site and the effects of the new site on the existing site should be considered. In certain cases, owing to age, technology and design, for example, plants on the same site could have different licensing requirements. The effects of a new installation on or near to an existing site should be assessed on the basis of the following considerations:
Any design, construction or operational restrictions arising from the way in which the existing installation is operated. For example, the heat sink requirements for the operation of existing installations may have significant bearing on the design of the heat sink system for a new installation.
The nuclear or radiological hazards arising from accidents at the existing installations or new installations involving the release of radioactive material, direct radiation shine or both.
Conventional hazards arising from accidents on the existing site, such as the release of toxic chemicals, explosions, missiles or flooding.
Interactions between the emergency arrangements for new sites and for existing sites.
Relevant hazardous events, such as loss of power supply from the electricity grid, and most external hazards, can initiate common cause failures on several or all of the nuclear installations on the site, and the effects of such common cause faults should be accounted for.
Hazards arising from accidents at both the new installation and the existing installation, and consequential impacts.
Compliance with dose constraints and risk constraints from the combined sites in both operational states (normal operation and anticipated operational occurrences) and accident conditions:
Where the new installation forms part of an existing site, the net effects of both installations in terms of safety should be considered with regard to:
Exposure of members of the public and environmental impacts in normal operation: It is to be expected that radiological consequences in operational states for members of the public may increase since the new installation will have an additional source term. It should be established whether this additional source term necessitates additional protection over and above what would be expected if the new installation were on an isolated site.
Exposures and risks in accident conditions: The new installation provides a contribution to exposure of and risks to members of the public in accident conditions. Where there are independent accidents at each installation, the increase in risk is likely to be small. The net combined contribution to risk should be determined, however. Where the accident initiator is a common cause event (e.g. a flood), then both exposure of and risks to members of the public should be assessed. It should be taken into consideration that all installations at the site may be simultaneously challenged by a common cause event and that consequences may be higher for the combined site. This may warrant additional safety measures being applied to the new nuclear installation or to both installations to meet dose constraints and risk constraints, and in order to keep exposures and risks as low as reasonably achievable.
Where the new installation occupies a separate site immediately adjacent to, or very close to, an existing site, it is to be expected that exposures and risks for people outside both sites will be similar to those mentioned in (i) above. Additional safety measures may still be necessary at one or both sites to keep exposure and risks as low as reasonably achievable.
3.27.
If different, the operating organization for the new site should provide the operating organization for the existing site with information on the issues mentioned above. It is therefore beneficial for both operating organizations to establish a good working relationship early on, so that relevant information can be made available to either operating organization as and when it is necessary.