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FINPSA TRAINING -R-, a PSA model in consisting of event trees, fault trees, and cut sets

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FinPSA Training, version

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To submit a request, click below on the link of the version you wish to order. Rules for end-users are available here.

Program name Package id Status Status date
FINPSA TRAINING2.2-R NEA-1916/02 Tested 25-AUG-2022

Machines used:

Package ID Orig. computer Test computer
NEA-1916/02 PC Windows PC Windows
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The FinPSA Training software is a risk and reliability analysis tool intended for PSA/PRA (probabilistic safety assessment/probabilistic risk analysis) modelling. The tool is designed to support the main activities related to PSA/PRA by easy model creation, analysis, traceability, reporting and information exchange capabilities. With the FinPSA Training version, it is possible to build moderately large models sufficient for in-depth training and most research applications.


A PSA level 1 model consists of event trees, fault trees and relating database information. The software generates minimal cut sets for event tree sequences based on fault trees linked to the columns of the event trees. Minimal cut sets are also generated for consequences, such as a core damage, by combining the minimal cut sets of the sequences leading to the same consequence. Total frequencies of the consequences and sequences are calculated based on the minimal cut sets and basic event data. Risk importance measure computation, sensitivity analysis and uncertainty analysis can also be performed based on the minimal cut sets.


The PSA level 2 modelling language allows dynamic modelling of a severe accident, where time dependencies are important. It links together parametric models describing plant behaviour, fission product evolution and probabilistic computations. For level 1 and level 2 integration FinPSA Training uses interface trees. The interface trees link event tree sequences to plant damage states.


The software keeps automatically track on edited parts of the PSA model. If PSA results already exist, they can be updated by automatically detecting changed parts of the model and calculating only the dependent results. The whole model can also always be calculated again.


See also FinPSA website


Note that the use of FinPSA Training is for the exclusive purpose of research and education. For other applications and/or commercial use, please contact VTT directly through the FinPSA website


In FinPSA version, the following fixes/corrections have been implemented on PRA levels 1 and 2:

  1. Issue causing user to be kicked out from FinPSA when editing local project table.

  2. In the risk integrator, issue causing floating point error during integration.

  3. In the risk integrator, issue causing an error message during integration with no information on error provided.

  4. In the risk integrator, bugs in outputting scatter plot results.

  5. In the risk integrator, Cet function contributions are correctly shown when “all variables” selected.

  6. In the statistical analyses of one CET, missing axis titles are added to scatter plots made of individual simulation points in general results.

  7. Distribution functions (DADD and DDIV) with two distributions as parameters issue.


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Level 1 part of FinPSA Training is based on event trees and linked fault trees. Minimal cut sets are generated for event tree sequences and consequences from the fault trees. Probabilities of the basic events in the fault trees are calculated based on reliability parameters using a reliability model depending on whether the basic event represents an operating or standby component.


Computation of the frequencies of consequences is performed based on the minimal cut sets and probabilities of basic events. It has three basic modes: S1-Sum, Mincut upper bound, and Mincut Accurate. Mincut accurate is based on minimized computing cross-products in series expansion. This is the most accurate method for minimal cut set quantification.


Interface trees are used to build a link between level 1 and level 2 models. They are like normal level 1 event trees, but instead of the initiating event, their starting point is a list of minimal cut sets. The purpose of the interface trees is to model containment systems and containment event progression. Thus, the end points of interface trees are plant damage states, which are the starting point of level 2 model. Similarly to level 1 methods, minimal cut sets are generated for interface tree sequences and plant damage states from the fault trees. Frequency computations of plant damage states are performed identically to level 1 computations.


Level 2 modelling is based on the containment event tree (CET) methodology. It links together parametric models describing plant behaviour and probabilistic computations. The CET model consists of a graphical event tree and associated models that are described in specialized CET programming language (CETL). CETs are solved by Monte Carlo simulations. Statistical analyses are performed for the simulation results automatically after the simulations, and the results of different CETs can be integrated into the overall level 2 results.

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Model size restrictions in FinPSA Training: 200 fault trees, 100 event or interface trees, 2000 basic events or gates, 5 columns/event or interface tree, 3 Containment event trees (CET), 6 columns and 15 sequences/CET, CETL code size 10 kB.


A commercial version without the above restrictions is available from VTT.

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FinPSA Training version has the same solver and computational performance as the full FinPSA Business version. Parallel computation is supported both on a single computer and over a network of several computers (shared projects). At the most 64 processes (cores) can perform computations in parallel. The example project is solved in seconds. The business version is used to solve full scope PSA models of nuclear power plants in reasonable time (1-24h).

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FinPSA has several advantageous features compared with many other PSA software.


Level 2: Dynamic containment event tree (CET) approach that supports integrated deterministic and probabilistic safety assessment. Dynamic CETs combine event trees with programmable parametric modelling. In dynamic CETs, the user defines functions to calculate conditional probabilities of CET branches, timings of the accident progression and amounts of releases using CETL programming language.


Task-oriented model for control systems: Complex I&C system models can be isolated from the system fault trees. Fault trees can refer to control tasks and control tasks can be linked to fault trees, e.g. for support functions like electric power or cooling. The I&C model is written in text format and it is based on communication vectors.

Traceability: Each minimal cut set can be traced back to the event tree and interface tree accident sequence. The failure propagation of any minimal cut set can be shown in the fault tree. Level 2 results can be also traced back to level 1 accident sequences.

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Package ID Status date Status
NEA-1916/02 25-AUG-2022 Tested restricted
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  • Tyrväinen, T., Silvonen, T., & Mätäsniemi, T. (2016). Computing source terms with dynamic containment event trees. In 13th International Conference on Probabilistic Safety Assessment and Management (PSAM 13) International Association of Probabilistic Safety Assessment and Management IAPSAM.

  • Björkman, K., Tyrväinen, T., Niemelä, I., & Mätäsniemi, T. (2013). Developing PRA computer code requirements based on probabilistic risk analysis practices. In Proceedings: International Topical Meeting on Probabilistic Safety Assessment and Analysis, PSA 2013 (pp. 1215-1226). American Nuclear Society (ANS).

  • Niemelä, I. 2012. Isolation of I&C model from PRA fault tree model. In: Proc. of 11th International Probabilistic Safety Assessment and Management Conference & The Annual European Safety and Reliability Conference, Helsinki, 25–29.6.2012, 10-We3-4.

NEA-1916/02, included references:
- Tero Tyrvainen, Teemu Matasniemi and Kim Bjorkman:
FinPSA User Guide, Release 2.2.0.x (Apr 27, 2022)
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It is expected that the computers for using the software have a network adapter and at least 2GB of memory per installation. Parallel computation with several cores may require more memory. At least 500MB disc space should be available. (The requirements are rather recommendations than strict requirements.)


Tested at the NEA Data Bank with:

  • Computer: AMD A6-9210 RADEON R4 2.40 GHz CPU Processor, RAM: 4.0 GB

  • Operating system: Microsoft Windows 10

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Package ID Computer language
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Windows 10

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VTT Technical Research Centre of Finland Ltd

P.O. Box 1000, FI-02044 VTT, Finland

Finpsa ( at )  

Contact for commercial use: Matti Paljakka Tel. +358 20 722 6423 matti.paljakka ( at )

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FinPSA - Software Installation - Guide for Training version.pdf -- Start your
study here
L2FinPSA.exe -- Main program
compiler.exe -- Compiler for PSA level 2 model development
FinPSA - Training - Loss of feedwater example.fpb -- FinPSA project/model
backup of the example model
FinPSA - Training - Loss of feedwater example v2.0.fpb-- FinPSA project/model
backup of the example model including PRA level 2 model and integration with
PRA level 1
readme.txt -- File description

/FinPSAUserGuide220x.pdf -- Comprehensive user guide
/FinPSA - Software use - Project basics.pdf -- Step-by-step guide to create your
first project
/FinPSA - Software use - Event tree actions.pdf -- Step-by-step guide to modify
event trees
/FinPSA - Software use - Cut set actions.pdf -- Step-by-step guide to analyse
cut sets
/FinPSA - Education - Concepts and traceability.jpg -- Overview of FinPSA
/FinPSA-VTT-poster training 2020-12-9.pdf -- FinPSA Traning poster

/FinPSA-RA2021-01_Training.doc -- RA (Receipt Acknowledgement) form for
requesting a license
/FinPSA-LA2016-01_v1.pdf -- License Agreement Terms
/FinPSA-PS2021-01_v4.pdf -- Software Product Specification
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  • G. Radiological Safety, Hazard and Accident Analysis
  • K. Reactor Systems Analysis

Keywords: event trees, fault tree analysis, probabilistic sys assessment, probability safety analysis.