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Assessment and safety justification

Safety critical control systems

​In regulated areas, such as nuclear power, healthcare, railroads and aviation, companies must justify the safety and security of control systems in an unarguable way. Doing this for complex systems is challenging and must cover both technical and organisational aspects. In particular, software-based systems have introduced new challenges in safety analysis and licensing.

Within the framework of multi-disciplinary and model-based Systems Engineering, VTT offers modelling and analysis methods and tools for the industry and regulators. Our independent assessment services cover a wide range from environmental testing and reliability analysis of control equipment to evaluation of human-machine interfaces and human organisations. Throughout the system design qualification and licensing, our solutions can be used to guide the design process and to collect evidences to show that safety requirements are satisfied. To justify the design decisions and conclusions made based on them, and to combine assessments of different components and engineering disciplines on the system level, we apply the structured assurance case approach. Explicit arguments that link evidences to claims about required functions and properties provide a transparent justification of system safety (see figure).


  • Cost-effective and high-quality assessments
  • Accumulation of safety knowledge
  • Reduced regulatory uncertainties, savings in terms of cost and time

J. Valkonen, T. Tommila, J. Alanen, J. Linnosmaa, T. Varkoi, Views on safety demonstration and systems engineering for digital I&C, 39th Enlarged Halden Programme Group Meeting, EHPG 2016, 8 - 13 May 2016, Fornebu, Norway. Institute for Energy Technology (2016), 13 p.

J. Valkonen, T. Tommila, J. Linnosmaa, T. Varkoi, Safety demonstration of nuclear I&C - an introduction, Research Report : VTT-R-00167-16, VTT, 2016 , 38 p.

T. Tommila, J. Alanen, Conceptual model for safety requirements specification and management in nuclear power plants, VTT Technology: 238, VTT, Espoo, 2015, 120 p. + app. 26 p.

J. Valkonen, S. Guerra, R. Bloomfield, N. Thuy, J. Märtz, B. Liwång, J. Hämäläinen, HARMONICS: EU FP7 Project on the Reliability and Safety Assessment of Modern Nuclear I&C Software, International Symposium on Future I&C for Nuclear Power Plants (ISOFIC 2014), Jeju Island, Repulic of Korea, 24 - 28 August 2014. Korean Nuclear Society (2014)

Integrated Safety Assessment and Justification of Nuclear Power Plant Automation (SAUNA)

The general objective of SAUNA (2015-2018) is to develop an integrated framework for safety assessment and transparent safety demonstration of nuclear power plant instrumentation and control (I&C) systems. Part of the project is dedicated to developing methods and tools for assessing the safety of systems and their development processes.

SAFIR2018 programme website:

Harmonised Assessment of Reliability of Modern Nuclear I&C Software (HARMONICS)

The objective of the HARMONICS project was to ensure that the nuclear industry has well founded and up-to-date methods and data for assessing software of computer-based safety systems. It proposed systematic and consistent, yet realistic and practical approaches for software verification, software safety justification and quantification of software failure rates. HARMONICS was funded by FP7 Euratom.

HARMONICS website: