As far as possible, there is a need that all plants take into account developments in safety standards and technology. It is unlikely that older plants will meet the same standards as modern plants but they must have adequate operating safety margins. These are assessed, for e. g. by following plant modifications, new fuel cycles and also during periodic safety reviews (PSRs), discussed in more detail later in the book. Most utilities are required by their regulators to carry out PSRs at regular intervals, typically at least every 10 years. The purpose of these reviews is to consider all facets of the long-term operation of the plants (rather than the particular every day running of the plant).

Considerable experience has been gained in the UK on the continued operation of nuclear power plants over the past 50 years. Some particular activities that are being carried out in support of the Magnox reactor programme (Mortin, 2000) are described below and are typical of the practices that need to be adopted for older generation plants. These are summarised in Table 2.7.

Plant maintenance and monitoring practices must be reviewed to take advantage of improved techniques. Particular checks must be made on the functional testing of

Table 2.7. Important issues for continued operation

Increased safety demands — impact of new standards and technology on performance and operation Plant maintenance and monitoring — availability of improved techniques Ageing — status of plant and how undesirable effects can be mitigated

Long-term technical support — availability of Suitably Qualified and Experienced (SQEP) personnel

Mortin (2000).

components and on equipment settings. If necessary, components under wear must be replaced. Another purpose of the reviews is to establish that the frequency and scope of inspections is optimal from the point of view of both safety and cost effectiveness.

The issues of structural plant ageing have to be addressed. Plant ageing can result from many wide-ranging and different phenomena depending on the plant in question. Pressure vessels may become embrittled as a consequence of high fluence particularly at welds. Chemistry effects such as oxidation of graphite cores is a particular issue in gas reactors that needs to be considered.

Another issue identified concerns the technical support of plant. There are issues arising from the potential loss of staff, perhaps recruited in the early days of plant operation but who may be nearing retirement several decades later. The problems of recruiting into a nuclear industry that may be scaling down are well recognised.