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Probabilistic Safety Analysis Expert Working Group

The Probabilistic Safety Analysis Expert Working Group is convoked by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit - BMU) and headed by the Federal Office for the Safety of Nuclear Waste Management (Bundesamt für kerntechnische Entsorgungssicherheit - BfE. The Working Group consists of technical experts who work at

  • Authorities,
  • Expert organisations,
  • Producers, and
  • Operators of nuclear installations as well as
  • Consultants

in the field of Probabilistic Safety Analysis (PSA). Until 30 July 2016, the Federal Office for Radiation Protection (BfS) had executed this task.

As an expert body, the PSA Expert Working Group advises the BMU in terms of question relating to the Probabilistic Safety Analysis.

What is a Probabilistic Safety Analysis?

The Probabilistic Safety Analysis (PSA) is a method of quantitative safety and risk assessment. It is an important component of the regular safety reviews of nuclear power plants. The PSA is based on a probabilistic approach (using probability models), i.e. the numerical description of frequencies and probabilities.

Tasks of the PSA Expert Working Group

The tasks of the PSA Expert Working Group include

  • The revision of the technical documents on the Probabilistic Safety Analysis,
  • The technical-scientific exchange of experiences in terms of methods, applications and important results of Probabilistic Safety Analyses at home and abroad,
  • The technical discussion of new developments in terms of methods, data and procedures, and
  • The determination of technical conformity or divergence of opinion with regard to technical-scientific questions concerning the implementation of PSA for nuclear power plants.

The expert working group generally meets twice a year to deal with these tasks. The technical-scientific exchange on special issues can be done in small working groups who present their results to the PSA Expert Working Group.

Technical documents on the Probabilistic Safety Analysis

Technical documents on the Probabilistic Safety Analysis in nuclear power plants (German only) Technical documents on the Probabilistic Safety Analysis in nuclear power plants (German only)Technical documents on the Probabilistic Safety Analysis in nuclear power plants (German only)

The generic official requirements as well as the extent and the depth of analysis of the Probabilistic Safety Analyses in the scope of the safety inspection is regulated in the "Guideline on the Performance of the Safety Review pursuant to § 19a of the Atomic Energy Act – Guide Probabilistic Safety Analysis for Nuclear Power Plants in the Federal Republic of Germany". As to concrete details in the implementation, the Guideline refers to the two technical documents on methods and data on the Probabilistic Safety Analysis for nuclear power plants (only in German).

The technical documents recommend and explain methods and data to implement a Probabilistic Safety Analysis. Thereby they increase the procedural safety for the concrete implementation of Probabilistic Safety Analyses and facilitate their assessment. In terms of their detailed methodical recommendations, the technical documents differ from most international guidelines or standards, which mostly set only a frame for the analyses to be carried out and do not include technical details and method descriptions or data.

Already during the period from 1993 to 1996, the PSA Expert Working Group had developed two technical documents on methods and data for the Probabilistic Safety Analysis for the purpose of the safety review pursuant to § 19a of the Atomic Energy Act. Together with the generic "Guideline", these volumes were comprehensively revised and expanded with respect to the extent of analysis between 1999 and 2005.

Supplementary document (German only) Supplementary document for the Probabilistic Safety Analysis (German only)Supplementary document on methods and data for the Probabilistic Safety Analysis for nuclear power plants (German only)

The basic idea of the third update, which started in 2008 and was completed in 2015, is the documentation of the comprehensive experiences from applications and the consideration of new developments in the field of PSA. For this purpose, the PSA Expert Working Group assigned four working groups to revise the following chapters and the relevant attachments:

  • Level 1 PSA based on low-power and shutdown modes,
  • Level 2 PSA based on full power operation,
  • Earthquakes and external flooding, and
  • Personnel actions with the objective for the generation of new methods.

The results were published in a supplementary document. The present supplementary document on methods and data for the Probabilistic Safety Analysis for nuclear power plants includes those sections of the documents from the year 2005 where modifications, extensions and updates were carried out (only in German).

Development of the technical documents of the PSA Expert Working Group

At the beginning of 2013, the "Safety Requirements for Nuclear Power Plants" were published. Thus, it is also necessary – beyond the safety review pursuant to § 19a of the Atomic Energy Act – to apply probabilistic methods, in order to evaluate the balance of the plant's safety design and the safety relevance of modifications to the plant or their mode of operation.

According to the safety requirements for nuclear power plants, events or phenomena that have occurred or become known during operation need additionally to be evaluated probabilistically. The PSA Expert Working Group has therefore established the "Probabilistic Safety Analysis in the Supervisory Procedure" Working Group at the end of 2012, whose task it is to develop methodical assistance for the application of the PSA according to the "Safety Requirements for Nuclear Power Plants".

In the context of a discussion on future topics and tasks of the PSA Expert Working Group, in particular the following topics were identified:

  • Issues relating to the post-operational phase,
  • Experiences with new methods, in particular regarding the assessment of human actions,
  • Level-2 PSA for the fuel element storage pool,
  • Initiating events and methods to determine the frequency of internal and external events.
State of 2018.07.13

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