DIN EN 62340:2010-12

In order to achieve a high safety level, redundancy is applied as one of the key features for designing instrumentation and control systems (I&C systems) important to safety. Since a common cause failure (CCF) would compromise the effectiveness of redundancy, it is essential to take adequate measures against it. This is one of the most difficult problems with regard to instrumentation and control systems important to safety, both in nuclear power plants as well as in other technical applications. Experts who were involved in the preparation of the standard have succeeded in integrating the different points of view into the standard so that they are the basis for the derivation of effective measures against CCF of instrumentation and control systems important to safety, without restricting to one particular solution in their wording. The standard addresses the whole scope of aspects to overcome common cause failures which are applicable for instrumentation and control systems important to safety. It contains requirements and recommendations for the architecture of I&C systems and gives an overview of all requirements relevant to CCF without overlapping with aspects already addressed in other standards (see for instance DIN EN 60709 (VDE 0491-7), DIN EN 60880 (VDE 0491-3-2) and DIN IEC 61513 (VDE 0491-2)). It provides instructions to reduce the possibility of the existence of mechanisms that could support the triggering of postulated types of latent software faults to cause CCF during transients. It also contains instructions for the design and implementation of independent instrumentation and control systems important to safety that operate from different signal trajectories so the likelihood of coincident failure of these independent systems is not relevant with regard to the intended plant life even if latent common software faults may exist. The responsible Committee is Subcommittee UK 967.1 "Leittechnik für kerntechnische Anlagen" ("Instrumentation and control of nuclear facilities") of the DKE (German Commission for Electrical, Electronic and Information Technologies) at DIN and VDE.