EVOLUTION OF SAFETY

This section considers the question on how safety standards are likely to evolve in the future. This is difficult to forecast in the present climate where in many countries in the Western world, there are few active initiatives for new build. Moreover, there are a large number of plants still currently operating of very different ages and very different design types. There has been a significant investment in upgrading certain classes of reactors, e. g. some of the older Russian-designed plants in Central and Eastern Europe, the early VVERs and RBMKs have a much more limited design basis than would be acceptable for licensing today.

There is general acceptance, at least within the nuclear community that most operating reactors in the world are safe. This is not the view of a large portion of the general public and the tendency will be a drive to continue to make reactors safer.

There is international pressure to improve and unify safety standards across the world. The IAEA standards are generally recognised as the starting point for most countries. These are generally taken as the basis for national standards in most countries, particularly in those with less well-developed nuclear regulatory frameworks.

There are also EC initiatives to develop common approaches in safety across Europe and the EU accession countries. There has resulted in a more unified approach across Europe with regard to regulator approaches; e. g. one principle is independence of the regulator from the licensee. However, there are limits in the level of unification that can be achieved at the technical level across such a diverse range of types of reactor in operation. Some plant component upgrades are possible to bring plants up to a higher level of safety commensurate with more modern plants, but it is difficult to improve the safety level of some elements of the design, e. g. strengthening of the containment.

The majority of proposals for new reactors has been ‘evolutionary’ water-reactor designs. These have a similar level of safety to that found in the more recent current generation plants but the evolutionary designs have some additional safety features. These include the use of passive systems as in the AP600 and 1000 systems, also the availability of ex-vessel flooding capability in these plants and core catchers as in the EPR and the latest VVER 1000.

However, for other reactor types the situation is much less clear. The requirements for the design basis of LMFBRs are much less clear, and how safety standards will evolve in relation to IAEA design requirements. Events such as large-scale sodium fires were originally taken as outside the design basis for LMFBRs based on probabilistic arguments. Some whole core accidents are taken to be within the design basis, thus requiring a higher integrity primary circuit.

The design basis for gas-cooled high-temperature reactors and how it should be interpreted in the light of IAEA design requirements is also as issue.

In future vendors will in practice demonstrate that their design meets IAEA standards (and Utility Design Standards) in additional to national requirements. In the US, the approach of design certification has been used for evolutionary plant. In principle, if a design is approved by the licensing authority in one country, this should at a minimum facilitate its acceptance in other countries. This is based on the assumption that regulators adopt common licensing approaches. A harmonised licensing regime would certainly be beneficial but this is not the present position even in Europe.

Some of the future designs under consideration in the GIF collaboration are not likely to come into commercial operation for many decades. It is probably premature to speculate on the licensing frameworks within which these designs will be licensed. However, it seems likely that any commercial designs that are eventually put forward for licensing will have been developed within increasingly global collaborations and will be licensed against more harmonised international safety legislation.

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