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Digital safety instrumentation and control important to safety in nuclear power plants

The safety instrumentation and control (I&C) automatically controls and limits safety parameter values like

  • pressures,
  • temperatures and
  • neutron flux densities.

If given limits are exceeded, safety functions like

  • power limitation,
  • turbine trip or
  • reactor trip

are triggered.

In the time of plant construction hardwired I&C equipment was installed based on analogue relay and transistor technology. Today the maintenance and, if necessary, the redesign of such an equipment requires a significant effort. Thus, the analogue I&C equipment is being replaced with software-based equipment, with which measured values and operating data are processed digitally, also in German nuclear power plants. Particularly, operationally used systems but also equipment of lower grade safety significance are affected. The central equipment of the reactor protection system for the processing of safety critical functions are still hard-wired, measured values and operating data being processed in an analogue way.

The Federal Office for the Safety of Nuclear Waste Management (BfE) supports the Federal Environment Ministry (BMUB)

  • in setting up the the requirements for safety related applications of digital I&C equipment in nuclear power plants,
  • in evaluating the industry-developed methods for demonstrating compliance and
  • if necessary, in the preparation of federal positions on licensing issues, especially for I&C functions with high safety importance.

For this purpose, BfE initiates and controls associated research projects. In addition, BfE participates in meetings of national and international working groups and contributes to their discussions and progress. Currently, the focus is made on I&C equipment which – outside of the central I&C –

  • gathers and processes measured values of the plant,
  • protects or activates safety-relevant aggregates, and
  • secures the energy supply of the safety-relevant aggregates.

Safety and security requirements for digital I&C

At present, BfE is involved in developing and defining the safety and security requirements for software-based I&C:

  • at national level as

    • nuclear regulatory framework (safety requirements for nuclear power plants),
    • Standards of the German Nuclear Safety Standards Commission (KTA-Kerntechnischer Ausschuss) in the form of the KTA standards of the 350x series,
    • Guidelines of the Association of German Engineers (VDI-Verein Deutscher Ingenieure) and
  • at international level as

    • Safety standards of the International Atomic Energy Agency (IAEA),
    • Guidelines of the European Commission (EC) and
    • Standards of the International Electrotechnical Commission (IEC).

Results of international working groups

Title of report "Licensing of safety critical software for nuclear reactors" Report "Licensing of safety critical software for nuclear reactors"Report "Licensing of safety critical software for nuclear reactors"

The report "Licensing of safety critical software for nuclear reactors - Common positions of international nuclear regulators and authorised technical support organisations. Revision 2015" describes the work of a group of I&C experts from the following regulators and safety authorities

  • BEL-V (Belgium),
  • BfS (Germany),
  • CNSC (Canada),
  • CSN (Spain),
  • ISTec (Germany),
  • ONR (United Kingdom),
  • SSM (Sweden), and
  • STUK (Finland).

The report provides common technical positions on a set of important licensing issues raised by the design and operation of safety critical software that is used in nuclear power plants for the implementation of safety functions.

A revision of the common position and recommended practices of the European Commission consensus document published in May 2000: "Common position of nuclear regulators for the licensing of safety critical software for nuclear reactors (EUR 19265)" is part of this report. The revised version of the report also contains a statement concerning the qualification of software-based field equipment installed outside the central I&C system, such as sensors and actuators.

Note: Since 30 July 2016, the BfE supports the BMUB at national and international level in the field of digital safety I&C in nuclear power plants as well as develops and supports corresponding research projects. It took over this task on 30 July 2016 from the Federal Office for Radiation Protection (BfS) that had been responsible until then.

State of 2017.03.09

© Federal Office for the Safety of Nuclear Waste Management