Composition of Safety and Cyber Security Analysis Techniques and Tools for NPP I&C System Assessment

Composition of Safety and Cyber Security Analysis Techniques and Tools for NPP I&C System Assessment

Ievgen Babeshko (National Aerospace University KhAI, Ukraine & Centre for Safety Infrastructure-Oriented Research and Analysis, Ukraine) and Kostiantyn Leontiiev (Research and Production Corporation Radiy, Ukraine)
DOI: 10.4018/978-1-7998-3277-5.ch008
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Abstract

Safety assessment of nuclear power plant instrumentation and control systems (NPP I&Cs) is a complicated and resource-consuming process that is required to be done so as to ensure the required safety level and comply to normative regulations. A lot of work has been performed in the field of application of different assessment methods and techniques, modifying them, and using their combinations so as to provide a unified approach in comprehensive safety assessment. Performed research has shown that there are still challenges to overcome, including rationale and choice of the safety assessment method, verification of assessment results, choosing and applying techniques that support safety assessment process, especially in the nuclear field. This chapter presents a developed framework that aggregates the most appropriate safety assessment methods typically used for NPP I&Cs.
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Introduction

Modern instrumentation and control systems used at NPPs are mainly complex digital systems responsible for safe plant operation. Such systems include thousands or even tens of thousands of different electronic components. Although digital I&Cs are utilized at NPPs already a long time, the development of methodologies for the NPP I&C safety assessment is still a critical issue. Safety assessment methodologies include probabilistic safety analysis, operating reliability and safety assessment, static and dynamic analysis of NPP I&C software (IEC, 2004; 2006; 2009; 2010).

Issues on operating reliability assessments we covered in our previous work (Babeshko et al, 2017), in this chapter we focus on probabilistic safety analysis and software assessment and testing issues.

There are several challenges regarding application of the safety assessment techniques:

  • Firstly, number of such techniques is very large and choice of appropriate technique (optimal in point of view solved task and assessed system) is a challenging problem: systematization and orchestration of these techniques is required to assure solving of the assessment task;

  • Secondly, required accuracy and trustworthiness of safety assessment must be provided. In this case several approaches are possible: to select one technique or to choose and configure several techniques which could be complemented by each other. Question to be answered is how to select and how to configure?

In our previous researches (Babeshko et al, 2011, 2015, 2017, Illiashenko et al, 2011) we have provided assessment idea based on combined assessment techniques usage. But obtained results don’t provide formal notations of techniques and, therefore, don’t allow to construct models and perform calculations.

St John-Green et al have confirmed necessity of combined security and safety assessment, but integrated approach is stated as to be provided.

Misztal has shown possible combination of FMEA and FTA, but other methods are not considered and assessment of possible benefit is not estimated.

Performed work related analysis has confirmed that researches in this field are in demand in different critical industries, including nuclear.

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Background

Reliability Block Diagrams

A reliability block diagram (RBD) is a graphical representation of a system's reliability. It shows the logical interconnection of (functioning) components required for successful operation of the system.

RBD allows performing system reliability (no-failure operation) calculation basing on known reliability of its elements.

Probability of no-failure operation in case of series reliability block diagram can be calculated as product of probabilities of no-failure operation of its elements:

978-1-7998-3277-5.ch008.m01
,(1) where pk – probability of no-failure operation of k-th element, n-number of elements in system.

The relation between failure rate and probability of no-failure operation is the following:

978-1-7998-3277-5.ch008.m02
,(2)

Basing on formulas (1) and (2) the following expression for failure rate can be obtained:

978-1-7998-3277-5.ch008.m03
,(3) where λk – failure rate of k-th element, n-number of elements in system.

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