THE STANDARD IEC 62340 NUCLEAR POWER PLANTS - IC SYSTEMS IMPORTANT TO SAFETY - REQUIREMENTS FOR COPING WITH COMMON CAUSE FAILURE (CCF)

摘要

The new standard IEC 62340 has been published in December 2007. This standard includes requirements on the design of safety I&C systems of NPPs firstly to avoid Common Cause Failures (CCF) of I&C systems and secondly to overcome postulated Common Cause Failures. The paper gives an overview about the standard IEC 62340. Following the thread through the text characteristics of I&C systems are discussed and preconditions which could lead to CCF. Based on these fundamentals, strategies are derived to overcome CCFs by use of independent (partial) systems. Specific attention is turned to application of functional diversity since that forms the only strategy to overcome faults in the specification of the I&C functions. In addition a connection is established between the measures to overcome CCF and the concept of defence-in-depth also applied in I&C of NPPs.Requirements are given to avoid CCF resulting from internal causes of I&C systems as well as due to shared components e.g. power supplies. In addition effects of failure propagation via communication networks, postulated software faults and failures due to maintenance during operation are dealt with.The subject of this standard is one of the most difficult issues for safety I&C in nuclear facilities but also in other commercial I&C applications. Therefore different approaches have been established. The standard IEC 62340 integrates such different approaches in a way that effective measures against CCF can be derived from it without fixing a singular technical solution.