Radiation And Reactor Theory (RRT)

Radiation And Reactor Theory (RRT)

RRT aims to act as a centre of excellence with regards to reactor physics and radiation transport knowledge and capability, with focus on:

  • Reactor physics and radiation analysis services to Necsa, as well as to national and international clients and collaborators; and
  • Research in the area of nuclear reactor calculational method and code development, with a specific focus on the creation of industry-relevant reactor calculational code systems.

The RRT Department is divided into three research groups: Radiation and Reactor Analysis (RRA), Reactor Dynamics (RD) and Methods And Code Development (MACD). The primary responsibility within RRT is offering calculational and theoretical support to the SAFARI-1 nuclear reactor and its related activities.

RRT regularly hosts training workshops on dedicated computational code packages. This photo was taken during the April 2018 training workshop on the thermal hydraulics code RELAP.

Research Programs

RRT conducts research in the areas of:

  • Design, development and implementation of computational methods in neutronics and thermal-hydraulics of research reactors, pressurized water reactors and high-temperature reactor;
  • Development, verification and validation of multi-physics computational schemes for high fidelity reactor modelling;
  • Development of state-of-the-art computational analysis schemes for activation, source-term, criticality and shielding assessments.

New area of active research recently involve

  • Development and implementation of computational methods for multi-objective optimization of research reactor utilization;
  • Incorporation of Artificial Intelligence (AI) and Machine Learning (ML) techniques in reactor analysis;
  • Development and implementation of methods for verification, validation uncertainty quantification in modelling;
  • Integration of plant data, simulation and experimental data;
  • Radiation damage modelling and analysis.


RRT continuously improves and develops the OSCAR reactor analysis code system for reactor analyses. The fifth generation of reactor analysis code system the (OSCAR-5) is currently being developed by RRT. OSCAR-5 was released to national and international interested parties in 2019. OSCAR-5 is a reactor calculational platform providing multi-code, multi-physics support for research, power and high-temperature reactor analyses. This code system will provide state of the art and innovative methods for reactor analyses. The capabilities of OSCAR are well in-line with international best-practice and novel work within the field of method and code development is ongoing in RRT. In this regard, some important projects include the development of time-dependent solvers in OSCAR, improvement of the OSCAR nodal solver, the coupling of the OSCAR nodal solver with state of the art thermal-hydraulics codes and the development of high performance, massively parallel full core transport solution methods.

The in-house developed OSCAR code suite has been used over many years for research reactor analyses by several institutions. The system is primarily used to support the operation of SAFARI-1 but is also applied at various other international research reactors such as HOR (at TU-Delft, the Netherlands), HFR (at NRG, the Netherlands) and MNR (at McMaster University, Canada) as a reactor analysis tool.

The OSCAR-5 reactor analysis platform

The OSCAR-5 system aims to allow for multi-code, multi-physics support for reactor analysis, with the primary aim to allow the use of fit-for-purpose tools in support of reactor operations. This implies finding a balance between the nature of a specific calculational application and the level of detail and fidelity utilized in achieving the result. The OSCAR-5 system is built around the concept of a code-independent, consistent reactor core model. This model is deployable to an extendable set of integrated target codes and manages the passing of data between these target codes. Currently fully coupled to the system is our in-house OSCAR nodal package, Serpent and MCNP.

To better serve the nodal package, OSCAR-5 also introduces a number of improvements to the front end of the calculational path. This includes additional lattice code options and a theoretically consistent step by step approach to move from a detailed heterogeneous model to an energy condensed homogeneous model. The system gives feedback at each step, to help the user improve the nodal model and to quantify the final error estimate associated with the model.

The OSCAR-5 package includes an extensive user guide and tutorials which cover multi-code applications to analysis scenarios such as detailed flux analysis, core-follow analysis, reload and core design calculations, as well as equilibrium and core optimization analysis. A constantly growing database of research and power reactor models is also distributed with the code, to illustrate the way in which the system can be used to model various plant configurations and how the multi-code approach allows for powerful and synergistic reactor modelling support.

Visualization of SAFARI-1 model developed in OSCAR-5 reactor analysis suit.


RRT provides a wide array of nuclear analysis services to both internal and external clients. In particular, we offer:

  • The deterministic and stochastic reactor core neutronic and thermal-hydraulic analysis
    • Core-follow, core design and core reload analysis
    • Core safety and thermal-hydraulic analysis
    • Isotope production planning

Tools: MCNP, Serpent 2, OSCAR (in-house deterministic package), RELAP, CTF, PLTEMP

  • Source term and activation analysis using tools such as:
    • Spent fuel inventory analysis, waste characterization
    • Fuelled target inventory, heat release and dose calculations
    • Activation of ex-core materials
    • The analysis in support of nuclear facility decommissioning


  • Shielding design and characterisation using tools such as:
    • Shielding design and optimization
    • Dose rate determination and shielding verification
    • Transport and storage cask heat deposition and shielding design verification


  • Criticality assessment using tools such as:
    • Criticality safety design and optimization of amongst others storage and transport vessels
    • Criticality accident alarm system analysis

Tools: MCNP, SCALE/KENO and Serpent

  • Development and implementation of RG-0016 regulatory compliance plans for calculational support

Result of neutron flux calculation in SAFARI-1 research reactor obtained with Serpent code.


RRT has a strong focus on training of staff both from the perspective of academic development as well as ensuring regulatory compliance by developing suitably qualified and experienced personnel for nuclear safety-related analysis. In particular, we provide:

  • In-house training programs to develop suitably qualified and experienced scientists and engineers in the areas of reactor physics, computational methods, thermal-hydraulics and nuclear engineering analysis
  • Lecturing and post-graduate supervision at various post-graduate university programs locally and internationally, for in-house staff and external students
  • Regular hosting of training workshops on dedicated computational code packages
  • Development and technical supervision of Masters and Doctoral topics in relevant fields

In staff development, RRT partners with universities locally and abroad, including the North-West University, University of Pretoria, Stellenbosch University, University of the Witwatersrand, University of Johannesburg, Penn State University and North Carolina State University.

In June 2018, Linina Bedhesi was featured in the magazine Public Sector Manager, as a young nuclear professional.
Photo credit: More Matshediso from Public Sector Manager

Link to the article: https://issuu.com/topcomedia/docs/public_sector_manager_june_2018_iss/28


  • In 2010, the OSCAR-4 development team received the prestigious National Science and Technology Forum (NSTF) award in the category of research for innovation.
  • In 2014, Dr Djordje Tomašević was awarded a certificate of outstanding contribution in reviewing, for the journal Progress in Nuclear Energy.
  • In 2015, Mr Saymore Chifamba, then graduate student at University of Johannesburg (UJ) who was supervised by RRT members, received the prestigious Chancellor’s Medal for the best Master’s student in the Faculty of Science at UJ.
  • In 2016, Mr Bernard Schlünz who was awarded the Category IV recognition award: To an upcoming member of age 35 or below for excellence in Operations Research practice by the Operational Research Society of South Africa (ORSSA) at their recent annual conference.
  • In 2019, Dr Pavel Bokov was appointed Adjunct Professor at the North Carolina State University
  • As of 2022, two RRT researchers hold C1 National Research Foundation (NRF) Ratings
  • Many RRT members have received awards for best student presentations at both local and international conferences.


In May 2010, the OSCAR-4 code development team won the prestigious NSTF (National Science and Technology Forum) award in the category of Research and Innovation. The photo shows Dr Djordje Tomašević receiving the NSTF trophy from the Minister of Science and Technology, Ms Naledi Pandor, on behalf of the OSCAR-4 team (which he leads).

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