IAEA activities on passive safety systems and overview of international development

Although a major focus of nuclear power reactor development efforts in industrialised countries is on large evolutionary units and design modifications that take maximum advantage of successful proven features and components, consideration is also given to utilisation of passive safety systems and inherent safety features. The various advanced reactor designs: evolutionary, large water-cooled reactor designs; evolutionary, medium size water-cooled reactor designs; concepts requiring substantial development; gas-cooled reactor concepts; and liquid metal-cooled fast reactors, incorporate a wide variety of passive safety features for initiation of safety systems, for residual heat removal and for containment heat removal. Organizations have established testing programmes to confirm their performance. A number of IAEA activities have lead. to the conclusion that the use of passive safety features can be a desirable method of achieving simplification and increasing the reliability of the performance of essential safety functions. However, care should be taken to evaluate possible new failure mechanisms, and both passive and active systems should be assessed from the standpoint of reliability and economics. Key technical issues include: the quantification of reliability over a wide range of conditions: economics, speed of action, plant ageing, demonstration of technical feasibility, in-service testing, ease of maintenance and minimization of personnel radiation exposure. Many member states conduct substantial work on the design, modelling, development and reliability assessments of passive safety systems. Continued information exchange can benefit the involved member states, and the IAEA is providing a forum for review of programmes, project directions, and the results achieved.