1.5.1 Existing Plants

Many LWRs operating in the Western world were designed according to US safety criteria and philosophy based on the defence-in-depth principle in design. This also includes the construction, maintenance and inspection and operational practices that were developed according to the US model. Some countries introduced country-specific regulations, e. g. associated with higher density populations or the requirement to withstand military aircraft crash, i. e. as in Germany. Nevertheless, the US historical influence has tended to encourage a process of harmonisation in the regulation of LWRs.

Within the Western world, there has always existed openness in communication at the level of research. This has had the result that significant differences in practices have been discovered. Regulators have been informed and the most advantageous common approaches adopted in many cases.

There are some areas where there has been a smaller level of harmonisation due to differences in safety philosophy because of redundancy requirements, levels of conservatism, etc. It is also difficult to develop a harmonised approach to safety criteria because of differences in plant design. Two particular areas are in the fields of fuel safety criteria and PSA.

In general, there is a greater degree of harmonisation in operational safety, in the requirements for Non-destructive Testing (NDT), on environmental qualification, the benefits of periodic safety reviews and the merits of risk based service inspection.

Some of the benefits of harmonisation for future plant are given below and also in Table 8.7.

1.5.2 Future Plants

There should be greater scope for a harmonised approach to licensing new designs. Already, this is happening for evolutionary reactors. Many of these have been designed against URs.

Table 8.7. Potential benefits of a harmonised approach to licensing

Achievement of a common licensing position across a number of countries would increase the common market

Common international standards for plant design would facilitate the licensing of plant

Harmonisation of design requirements, enabling design certification would benefit vendors

A harmonised regulatory approach would benefit utilities by reducing uncertainties in the licensing process

EUR 20055 EN (2001).

For example, designs have been specified by utility companies in Europe in consultation with regulatory authorities. A good example of this approach is the EPR French-German co-operation. Another co-operation involved the Westinghouse 1000 MWe passive plant reactor development programme, the Siemens 1000 MWe BWR and the Westinghouse Atom BWR90 +.

Harmonisation of EURs provides a focus for utilities and is more important than harmonisation in international working groups, which may be less focussed on utilities’ specific requirements.

Harmonisation can result from a design certification process, as adopted for AP600 and which is in progress for AP1000.

Another means to improve harmonisation would be in the common development of standards but this is not currently the situation.

Harmonisation of approach has resulted in increased consideration of severe accidents at the design stage.