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NKS Programme Area:
Strategies for Reactor Safety
The NKS/RAK-1 project formed part of a four-year nuclear research program
(1994-1997) in the Nordic countries, the NKS Programme. The project aims were
to investigate and evaluate the safety work, to increase realism and reliability of the
safety analysis, and to give ideas for how safety can be improved in selected areas.
An evaluation of the safety work in nuclear installations in Finland and Sweden
was made, and a special effort was devoted to plant modernisation and to see how
modern safety standards can be met up with. A combination of more resources and
higher efficiency is recommended to meet requirements from plant modernisation
and plant renovations. Both the utilities and the safety authorities are recommended
to actively follow the evolving safety standards for new reactors.
Various approaches to estimating LOCA frequencies have been explored. In particular,
a probabilistic model for pipe ruptures due to intergranular stress corrosion
has been developed. A survey has been done over methodologies for integrated
sequence analysis (ISA), and different approaches have been developed and tested
on four sequences. Structured frameworks for integration between PSA and behavioural
sciences have been developed, which e.g. have improved PSA. The
status of maintenance strategies in Finland and Sweden has been studied and a new
maintenance data information system has been developed.