Proven engineering practices and operational experience

For reactors of an evolutionary type, wherever possible, the design should use structures, systems and components (SSCs) with previous successful applications in operating plants, or at least take due account of relevant operational experience which has been gained at other plants. 

Available operating experience should be taken into account in the safety assessment with the aim of ensuring that all relevant lessons in the area of safety have been adeqnately considered in the design. Operating experience should be a fundamental sonrce of information to improve the defence in depth of the plant. 

Extrapolative analysis from a real event seqnence to what might ultimately have happened in a plant if there had been additional malfunctions (compared with the malfunctions which happened in the real situation) has been demonstrated to be a nsefnl design tool. 

For example, passive safety systems are independent from external support systems such as electric power and have the potential for being simpler and more reliable than active systems. However, the actual performance and reliability of passive systems should be convincingly proven by appropriate and thorough development, testing and analysis programmes. 

The objective of the defence in depth strategy as indicated in para. 2.10 of Ref. [1] is twofold first, to prevent accidents and second, if prevention fails, to detect and limit their potential consequences and to prevent any evolution to more serious conditions. 

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