AYES, a major actor in Reliability Studies for Nuclear Safety Systems

Author : Mrs. Eleonora V., Consultant Engineer at AYES Switzerland GmbH

IEC 61513 is an international standard providing guidelines for the development of Instrumentation & Control safety systems of a nuclear power plant lifecycle.

Safety level classification: a critical responsibility

In the nuclear sector, safety classification of nuclear power plant (NPP) systems and sub-systems is one of the fundamental safety concepts used by national nuclear regulators, standard development organizations (SDO) and NPP suppliers in order to ensure that the plants pose minimal risks to public safety.

However, there are many ways to implement safety classification schemes, which result in different criteria being applied to the design and manufacturing of the structure, systems and components of the Instrumentation & Control (I&C) in nuclear power plants.

This increases the complexity of the compliance analysis and reliability demonstration studies of the systems classified as safety and those of the related safety-related components. Moreover, the different approaches of regulators, SDOs and suppliers have generated additional costs during the development of nuclear power plants.

The new IEC 61513 regulation aims at introducing the concept of a global safety lifecycle approach for the whole I&C nuclear power plant architecture and its individual systems in order to harmonize those criteria.

It reorganizes the classification and categorization process for safety systems and functions, no longer only derived from the safety level of the particular system, but by implementing a top-down approach in designing the whole safety lifecycle system and guaranteeing the correct level of reliability of safety systems within the I&C of the NPP as a whole.

Therefore, nowadays, to achieve proper safety classification of the I&C systems functions, it is necessary that process and safety engineers, international authorities as well as all parties involved have a common understanding of the criteria for classifying the I&C systems into one of the various categories.

The Uninterruptable Power Supply (UPS) System

The UPS System is an example of safety NPP systems. It consists of various category A functions (the highest safety level). The UPS system design, development and manufacturing process undergoes the most recent, accurate and demanding requirements, resulting from its possible interaction with the I&C of the nuclear power plant.

The standard management V-model implemented for the design, validation and development of UPS systems must be adapted in precise studies in order to comply with the new regulation.

This approach must be conducted in each phase of the validation management process, from the concept design to the factory implementation. Therefore, designing UPS systems has led to significant challenges for the project execution.

AYES providing technical added-value in multidisciplinary tasks

AYES is playing a leading role in supporting the customer on the whole process. Electrical and process engineers cooperate to ensure the high-quality standards of the UPS system for the mission critical application.

This results in designing systems which are more reliable & resistant to hazards. It also contributes to improve the customer requirement management system.

AYES engineers have been involved in various critical tasks such as: quality assurance, validation management procedures, technical system design specification, reliability demonstration reports, hardware and firmware design, modification, implementation and integration, as well as testing.