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Conference Article: Safety Classification and Defence In Depth For HTRS

Abstract

A suitable safety classification of systems, structures and components as well as a solid defence in depth in the design of nuclear power plants are considered to be amongst the most important fundamentals of safe nuclear reactor design and operation. The principles generally in use at present, as well as IAEA suggested principles, are heavily biased towards Light Water Reactor (LWR) design practices where active defence in depth is essential. Applying these principles to advanced reactors that are designed to preclude core or extensive fuel damage for all thinkable conditions, would result in considerable overdesign, and may even impact negatively on the overall safety of these designs. Over the past five years, the Pebble Bed Modular Reactor (PBMR) design team has reviewed existing legislation and guidance documents with a view to extracting the underlying safety philosophy, and has applied this to a consistent set of criteria to be used in the safety classification. Coupled to this, the defence-in-depth definitions for High Temperature Reactors (HTRs) of the design represented by PBMR have been developed to show compliance with existing principles, but with a different emphasis on the importance and execution of the various levels of defence in depth as suggested by the IAEA. A classification system that includes recognition of the long times available to take action before significant releases could occur is proposed and linked to the defence in depth requirements.

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Reference:

Proceedings of the Conference on High Temperature Reactors, Beijing, China, September, 22-24, 2004

International Atomic Energy Agency, Vienna (Austria)

HTR-2004, pp:1-7