Preface and summary of the United Kingdom contributions

The mechanical integrity of engineering structures is a matter of great practical importance for both economic and safety reasons. In practice this integrity must be assured by careful attention to many aspects of design, materials, fabrication, inspection etc. An important uncertainty is the possible presence of defects in the structure. Under appropriate circumstances, such defects can grow during service until they reach the size where they extend unstably and thus cause the failure of critical sections of the structure and the structure itself. The design and operation of these structures must therefore take account of the possible presence of cracks. The conventional approach is one based upon a set of conservative assumptions about the maximum defect size, nature and frequency of loadings on the structure, the materials properties, particularly crack growth rates and fracture toughness, etc. However many of these quantities are statistically distributed and we can never be absolutely sure that values worse than the chosen conservative limits will not be encountered. This is probably true of the relevant materials and must likewise be true of transient loadings. These uncertainties therefore oblige us to try to reduce failure probabilities in plant components by design, materials selection, manufacture, quality control, and pre-service and in-service inspection and monitoring. At this Specialist Meeting we are going to concentrate on in-service inspection and monitoring of LMFBRs. However, the techniques applicable to in-service inspection can of course be applied pre-service and it is generally recognised in the United Kingdom that there is a great need for intensive inspection of LMFBR plant both during and on completion of manufacture. Current experience indicates that design proposals for new reactors should pay particular attention to access, inspectability and replaceability. Because the environment experienced by components in large sodium cooled fast reactors represents a major departure from that in conventional generating plant and thermal reactors, these requirements for LMFBRs should be kept under constant review during the development stages. Since outage costs can be very high, advantage should be taken of any significant reduction in outage times that can come from early warning, from in-service inspection and monitoring, of developing faults and deterioration processes which could result in component failure