In this publication an NPP is considered to consist of one or more nuclear power reactor units located in a given site, whether fully separated from one another or sharing some common structures, systems and components. These units may exist under a single licence or multiple licences as established by the regulatory authority.
The significant differences of an NPP compared with a conventional power plant, with respect to site specific aspects, relate to the need to maintain some of the cooling function of the reactor core safely and reliably during an extended period after shutdown, and the strong emphasis on consideration of extreme hazardous events (i.e. events of very low annual frequency of occurrence and high intensity), through the assessment of all potential credible types of sources, whether from internal, natural or human‑induced (external) causes.
The term ‘site area’ is defined as a geographical area that contains an authorized facility, activity or source, within which the management of the authorized facility or authorized activity or first responders may directly initiate emergency response actions. This is typically the area within the perimeter fence or other designated property marker. This publication refers to the site as housing an NPP constituted by one or several reactor units and all associated facilities. For the purposes of this publication, the term ‘site’ is considered to be the same as ‘site area’.
In addition to a proper space to accommodate the layout for one or more power reactor units to be built in one or more phases, the siting and site evaluation processes ought to consider that an NPP requires other supporting facilities as follows:
Availability of land for the proposed number of power reactor units, together with auxiliary facilities. This will ideally include the area that will be required temporarily during the construction of the plant units, with enough space for accommodation, canteens, training, first aid, etc., for the substantial temporary labour force. Additional land ought to be identified and earmarked for an eventual exclusion area, to prevent population settlement or industrialization during the consideration of the potential site.
Availability of land for nuclear waste or spent fuel management facilities, as discussed in Section 2.6.
Considerations related to the siting of nuclear waste facilities are not developed in this publication, but they are presented in Refs [11–15].
During the siting process, the areas or sites are evaluated through the use of a specific set of attributes, which are defined in quantitative terms by assigning quantitative criteria to each. Although a great number of attributes may potentially be used to describe a site or area, attributes used at this time are only those for which criteria can be developed to discriminate among the areas or sites. Those attributes for which there is no useful information, or that are generally similar across the entire area to be evaluated, are not used for the siting process as they will not help to show differences between sites. When a site is finally selected for detailed site evaluation, additional specific information on all relevant attributes will be collected.
The selection of a suitable site for an NPP involves considering a large number of attributes in order to reach an optimal decision. In general, decision making problems with multiple criteria for the screening, comparing and ranking of different options involve a set of alternatives that may be in conflict with each other; in other words, a site may be optimal for some criteria but not for others, forcing a decision among sites of which none are completely optimal.
If the criteria applied are too general, they will not narrow down the areas of interest sufficiently. Equally, if the criteria are too limiting, the process may eliminate suitable sites in the early stages of the siting process. For example, the adopted criteria may be based on a certain technology with a defined seismic capability (i.e. the ability of the technology to withstand the calculated maximum earthquake effect, as discussed in Ref. [19]) and using sea water cooling; but it may then be found that there are no suitable sites complying with both of those conditions. In that case, it will be necessary to repeat the evaluation, changing the criteria to either allow the use of cooling towers or accept a greater seismic capability (recognizing the additional costs). As another example, it may be decided during the course of the process to separate higher level attributes into smaller increments and apply separate criteria to each of them, facilitating a more detailed analysis of those attributes that are particularly important for decision making.
In any case, the criteria have to not be out of conformance with the national site related regulations and IAEA safety requirements. Therefore, modifications to the exclusionary or discretionary attributes and criteria are either to select new attributes not formerly seen to be necessary for decision making, to change the definitions of the criteria to reduce the size of the error bands surrounding the initially selected criteria values (thus introducing additional but acceptable uncertainty) or to collect further site specific information to better define those attributes at the site being evaluated. Therefore, it is important to benchmark the selected attributes so that the criteria applied are neither too general nor too limiting, while recognizing that the results may still necessitate reviewing and modifying the defined criteria.