Description of Requirements to Safety Important I&C Systems

Description of Requirements to Safety Important I&C Systems

Yuri Rozen (State Scientific and Technical Center for Nuclear and Radiation Safety, Ukraine) and Serhii Trubchaninov (State Scientific and Technical Center for Nuclear and Radiation Safety, Ukraine)
DOI: 10.4018/978-1-7998-3277-5.ch003
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Abstract

The requirements for safety important instrumentation and control (I&C) systems, their components (software and hardware complexes, equipment), and processes of their development are provided. The reliability of I&C systems and their components are ensured by the requirements for prevention and protection against common cause failures, compliance with the single failure and redundancy criteria, and prevention of human errors. The requirements for operational stability of the components cover resistance to environmental impacts, mechanical (including seismic) and other external impacts, and insensitivity to changes in power supply parameters and electromagnetic interference. Requirements for the performance quality include characteristics pertaining to the accuracy and performance time of functions. Requirements for independence ensure that the system remains operable if its components fail and that the effects of electromagnetic radiation, fires, breakdown of insulation, and leaks in cables are minimized.
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Introduction

The steadily growing role of modern instrumentation and control systems in ensuring the safety and security of nuclear power plants requires that:

  • the properties of each system and its components comply with requirements of national and international regulations, rules, and standards on nuclear safety at all life cycle stages and

  • the procedure for the development, design, manufacture, testing, acceptance, and operation of the system itself and its components, established by regulations, rules, and standards on nuclear safety, be observed.

The purpose of this chapter is to show the requirements for the properties (parameters and characteristics) of I&C systems and their components that ensured safety when used for automation of nuclear power plants (NPPs).

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Background

The experience of the world community in standardizing, ensuring, and assessing the safety of I&C systems has been accumulated in the requirements of international and national standards and regulatory documents and taken into account in the large-scale upgrading process carried out as part of the programs to improve the safety and extend the life of existing power units. The upgrade process was based on the use of modern information technologies, new electronic components and computer facilities, optical transmission networks, and diagnostic, display, and archive computer tools.

The requirements set forth below for I&C systems important to safety and their components are determined by the applicable requirements presented in:

  • Safety Standards of International Atomic Energy Agency (IAEA): IAEA, 2016а; IAEA, 2016b; IAEA, 2016с; IAEA, 2010, etc.

  • Standards of the International Electrotechnical Commission (IEC): IEC, 2011; IEC, 2009; IEC, 2007; IEC, 2006; IEC, 2005, etc., and identical European standards related to of I&C systems important for NPP safety: EN, 2013; EN, 2010a; EN, 2010b; EN, 2015, etc.

  • Reports of the Western European Nuclear Regulators Association (WENRA): WENRA, 2014a; WENRA, 2014b, WENRA, 2012.

  • Regulations, rules, and standards on nuclear and radiation safety in force in Ukraine: NP, 2008; NP, 2015; NP, 2016a; NP, 2016b, etc.

  • IEC industrial standards, European standards, and state standards of Ukraine identical to them.

Key Terms in this Chapter

Life cycle: A set of stages for development, commissioning, and use of a system (component) within a time period that that begins from the concept development and specification of technical requirements and ends when the system (component) is removed from service when its further use is impossible or inexpedient.

Diagnosis: Determination of the technical condition of a system (component) and detection and identification of its inoperative components at the appropriate level of disaggregation.

Redundancy: Application of additional tools and/or capabilities that are redundant to those that are minimally required for function performance.

Common Cause Failure: Simultaneous failure of two or more elements in different redundant channels resulting from the same cause, which may lead to a failure of the I&C (HSC) function.

Diversity: Is a way to reduce the likelihood of common cause failure of two or more redundant systems, components, or channels that independently perform the same function though specially provided differences between these systems (components, channels) implemented at the stage of their design, development, and/or manufacture.

External Factors (EFs): Factors that can occur in places of hardware location and include: environment EFs (temperature, humidity, barometric pressure, ionizing radiation, corrosive agents, dust), mechanical EFs (vibrations, strokes, seismic effects), power supply EFs, specific environment EFs (water and solutions that can affect devices in accidents and decontamination fluids), and electromagnetic EFs.

Single Failure Criterion: Criterion that requires an I&C system (SHC) to perform all specified functions in any postulated initiating event (PIE) combined with a failure of one (any) element independent of this PIE.

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