Working Party on Scientific Issues and Uncertainty Analysis of Reactor Systems (WPRS)


Under the guidance of the Nuclear Science Committee (NSC), the Working Party on Scientific Issues and Uncertainty Analysis of Reactor Systems (WPRS) studies the reactor physics, fuel performance, and radiation transport and shielding in present and future nuclear power systems. The working party also studies the uncertainties associated with the modelling of these phenomena, particularly the modelling of reactor transient events.  


The WPRS's objective is to provide member countries with up-to-date information to preserve knowledge on and develop consensus in the following areas:

Reactor physics aspects considered include:

Radiation transport and shielding aspects, which are addressed in the Expert Group on Physics of Reactor Systems (EGPRS), include:

Reactor core thermal-hydraulics  aspects include:

  • methodologies for modelling on different scales
  • technics for high to low fidelity/resolution model data exchange (Hi2Lo)
  • fluid structural mechanical interactions for normal and deformed cores
  • preservation of experimental data

Fuel performance aspects include:

Multi-physics aspects include:

  • coupled neutronics/thermal hydraulics transient modelling
  • benchmark comparisons
  • sensitivity analysis.

WPRS and its expert groups co-ordinate several benchmark activities on reactor single- and multi-physics. The annual WPRS Benchmarks Workshops (typically one week with two parallel tracks of technical sessions) serve to exchange on the status of the benchmarks activities and discuss benchmark specification updates.

The WPRS structure of expert groups, technical review groups, and benchmark groups  is shown in the structure graph below

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Publications and reports
WPRS structure

Click on elements in graph above to jump directly to a specific WPRS activity.

WPRS organisation

Chair Kostadin Ivanov (USA)
Vice-Chair Hakim Ferroukhi (SUI)

All NEA member countries 

Full participant European Commission (under the NEA Statute)

Observer (international organisation)

International Atomic Energy Agency (by agreement)



NEA Secretariat: Oliver Buss 


Meetings, workshops and conferences

WPRS and associated Expert Group meetings are held approximately every twelve months. 

Next meeting: 20th Meeting of WPRS, 20 - 24 February 2023

Members' working area

The participants' working area is now hosted on MyNEA SharePoint 

Please follow these steps to sign in to MyNEA SharePoint:

  1. On the SharePoint sign in page, enter your email address as your username. Then type in your NEA password (reminder).
  2. A two-factor authentication is needed to log in. Select ‘MyNEA Access Authentication Agent 3.1’ as next step, which is the service for delegates.
  3. You will receive an email with an additional access code. Enter the access code on the website.

The MyNEA End User Guide is available online here: User's guide: myNEA

Related initiatives

Prior to the creation of the WPRS, a number of reactor physics benchmarks were undertaken.

Reactor types considered include, but are not limited to the following:

  • present generation light water reactors (LWRs) with advanced and innovative fuels, evolutionary and innovative LWRs and heavy water reactors (HWRs)
  • advanced reactor systems
  • accelerator-driven (sub-critical) and critical systems for waste transmutation.

The WPRS liaises closely with other NEA working groups, especially those operating under the guidance of the Committee for Technical and Economic Studies on Nuclear Energy Development and the Fuel Cycle (NDC) and the Committee on the Safety of Nuclear Installations (CSNI) in order to ensure the respective work programmes are complementary and to provide advice and support where required and undertake common work where appropriate. Particularly close working relationships are maintained with the Working Party on Scientific Issues of Advanced Fuel Cycles (WPFC), the Working Party on Multi-scale Modelling of Fuels and Structural Materials for Nuclear Systems (WPMM) and other relevant NSC working parties.


The current structure of the working party and its expert groups results from a major restructuring in 2020 in which the following expert groups were integrated in WPRS:

Benchmark Activities on Reactor Single- and Multi-Physics of the Working Party on Scientific Issues and Uncertainty Analysis of Reactor Systems (WPRS)

The Working Party on Scientific Issues and Uncertainty Analysis of Reactor Systems (WPRS)  and its expert groups co-ordinate benchmark activities on Reactor Single- and Multi-Physics. The benchmark activities serve the WPRS objectives to: 

  • provide Members with up-to-date information, preserve knowledge on, and develop consensus regarding reactor physics, thermal-hydraulics, radiation transport and dosimetry, and multi-physics aspects associated with nuclear power systems, aimed at providing the technical underpinnings of assessment of system performance and safety.
  • provide advice to the nuclear community on the developments needed to meet the requirements (data and methods, validation experiments, scenario studies) for the assessment of different reactor systemsprovide training and educational material to the nuclear community, to assist with developing future technical expertise within member countries. Workshops will be held on WPRS benchmarks
  • provide training and educational material to the nuclear community, to assist with developing future technical expertise within member countries. 

 The activities address the the following reactor types:

  • Current fleet of light-water and heavy water reactors (LWRs/HWRs) as well as present generation of fuel designs.
  • Evolutionary and innovative LWRs/HWRs along with advanced and/or accident tolerant fuel designs.
  • Next generation of reactor systems including water cooled small modular reactors (SMRs), micro-reactors, high temperature gas cooled reactors (HTGR) as well as advanced fast spectrum systems including sodium fast reactors (SFRs) and molten salt reactor systems (MSRs).
  • Accelerator driven (sub-critical) and critical systems for waste transmutation as well as fusion systems.