Belgacen Hizoum

Belgacem Hizoum

Senior Software engineer Thermal-hydraulic

  • Belgacem Hizoum is a Senior thermal hydraulic engineer at ORNL responsible for subchannel code CTF closure models development and improvement for BWR application.  He received his master’s degree in (1992) in nuclear engineering at Development Center of Energetic Systems Institute, Algiers, Algeria and another master's degree (2000) in mechanical engineering from university of New Orleans (UNO). His areas of research are in thermal-hydraulics system modeling, multi-phase flows closure model development and improvement, computational fluid dynamics, and improvement of numerical methods for solving engineering problem. He posited a vast experience in application of numerical methods for solving engineering problems, with deep knowledge of finite element method, finite differencing, and finite volume methods for code development. He is also proficient in debugging huge undocumented legacy FORTRAN code, maintenance, enhancement, development, testing, and documentation preparation. Prior to ORNL, Belgacem was a senior engineer at General Electric where he made a lot of contribution to the development of the GE subchannel code COBRAG and other codes such as core monitoring code AETNA, system thermal hydraulic code (TRACG), ISCORE.  He is the author of several papers geared toward development of new models related to mechanistic film dryout, void drift, mixing, liquid split at the transition to annular flow, deposition/entrainment, interfacial shear, and transition to annular flow criteria.


  • Master’s Degree in Mechanical Engineering- Focused on Numerical Methods (Finite Elements, Finite Difference, Boundary elements, Finite Volume, Discontinuous Galerkin Finite element method) Applied to; Heat Transfer, Fluid Dynamic, and Solid Mechanics, University of New Orleans, Louisiana, 1998-November 2000.
  • Master’s Degree in Nuclear Engineering- Focused on Stress analysis, Development Center of Energetic Systems Institute, Algiers, Algeria- Oct. 1992
  • Bachelor’s Degree in Mechanical Engineering, Majoring in stress analysis and Minor in combustion Engine Design, University of Sciences and Technology Houari Boumediene, Algiers, Algeria- July 1991.
  • Certificate of Nuclear Reactor Operator- Chinese Institute of Atomic Energy Beijing, China- June 1995.
  • Certificate of Nuclear Reactor Management and Maintenance- Chinese Institute of Atomic Energy Beijing, China- March 1993.

Professional Experience:


Senior Software engineer Thermal-Hydraulic, ORNL, Knoxville, Tn, 2020 to present

  • Reviewed and assess CTF closure models to improve the code capability to predict correctly void fraction.  The review revealed deficiency in the interfacial shear model and flow regime map.   A drift flux approach was derived and implemented into the code for redistribution of the vapor produced by boiling across the channel, which incorporates a novel correction for the subcooled boiling region.  Additionally, the flow regime map used by CTF has been significantly improved to provide more mechanistic predictions of changes in local flow conditions and topology.  Testing of the code showed that the modifications incorporated to the code significantly improve the void fraction prediction.  This work is being published in Nureth19 conference. 
  • Revised CTF numeric to resolve convergence issue and limited simulation time step. This includes Implementation of fast numeric’s through enforcing fully implicit discretization of all terms in the conservation equations and introducing an outer iteration to ensure convergence before marching to new time step.  The initial assessment of the improvement looks promising however still development is needed to contain numerical pressure spike due to condensation of vapor which is currently leading to limiting the time step.
  • Added to CTF pressure stretching model to contain pressure numerical spike and virtual mass model to preserve the hyperbolicity of conservation  equations
  • Provided support to expand code capability to handle simulation of bypass, water, and part length rods
  • Led a team to Develop and implement a new two-phase flow multiplier correlation for the wall shear model to improved CTF pressure drop prediction.  Assessment of the correlation showed remarkable improvement of CTF in pressure drop prediction.  This work is schedule to be published.
  • Contribute to the development and integration of a drift flux base subchannel code Alternate Non-linear Two-phase Solver (ANTS), into the CTF environment for future VERA applications and design scoping.
  • Successfully interacted with outside company (Ge) and obtained void fraction experimental Data. The data was added to CTF test matrix and is being used for benchmarking and improvement of the subcooled boiling model and void drift & mixing.
  • Reviewed CTF wall & Interface heat transfer, Grid loss, Mixing & Void drift.  Recommendations were made to these models to improve the overall CTF predictive capability.
  • Contributed to several proposals and provided Technical Support to CTF development and general thermal hydraulic consulting to resolve on timely manners challenging problems.

Senior Engineer, Thermal Hydraulic, GNF, Wilmington, NC, 2006 to 2020

COBRAG Subchannel code Development:

  • Responsible engineer of sub-channel code COBRAG. This included error correction, enhancement and documentation preparation.
  • Led a team effort to improve the overall predictive capability of COBRG01A with most of the investigations centered toward removing COBRAG empirical correlation and replace them with better first principal models.  This included:
  • Successfully Improved COBRG Film spreading to reduce the spread in the predicted critical film thickness at higher mass flux.
  • Implement, tested and Enhanced heat flux-based entrainment to improve COBRG02P critical power prediction at high mass flux.
  • Developed and implement a new deposition Model: Benchmarking of COBRAG showed weakness of COBRAG deposition model to predict accurately entrainment fraction. Several publicly open correlations have been tried, and testing.  Results showed that these correlations although may give satisfactory result for entrainment fraction but failed to predict correctly critical power. Thus, led us to develop a new deposition correlation that satisfies prediction of both entrainment fraction and critical power.
  • Improved COBRG01A void drift model. Assessment of COBRG showed weakness of void drift model to predict correctly local subchannel void fraction.  The improved void drift proposed in showed good agreement with the data.
  • Successfully, derived, implemented, and tested a mechanistic film dryout correlation based on selected non-dimensional conditions parameters at which the liquid film in annular flow breaks down. Results of comparison to experimental data improves the accuracy of dryout predictions
  • Diligently contribute to development of customer CTQ for COBRAG application methodology.  The development envisaged establishing high level acceptance criteria to each application categories and incorporates these in COBRG02P Software Requirements Document (SRD) and/or Software Test Plan (STP). The proposed CTQ was presented, reviewed and approved at Special Purpose Technical Design Review meeting.
  • Established scientifically demonstrated COBRAG validation process through expanding its test matrix to provide sufficient of the predictive capabilities of the code for separate effect and integrated systems.
  • Developed and implement a liquid partition model: Scrutiny of COBRAG predictions showed shortcoming of COBRGA in the partition of liquid at the onset of annular flow regime which is very important to obtain good prediction of critical power.   To overcome this, a new in-house correlation based on experimental data was developed and implemented into the code. Assessment of the code indicates that this model gave satisfactory results.
  • Implemented and tested GNF3 Subchannel pattern for use in optimization of the GNF3 design.
  • Successfully Converted COBRG02P to Intel compiler. Implemented OpenGE source control utilizing Git modern source control platform. This provided a streamlined process to archive and truck code changes and hence cut time in finding root cause of unexpected problems. 
  • Provided consulting and support in development and implementation of a new method-D correlation for accurate prediction of local loss pressure drop at high power.
  • Corrected number of errors and resolved on timely manner unexpected challenging problems such as convergence due to introduction of new model, modeling issue or existing problems such as asymmetry in void in both developmental version and the current level 2 codes and file a problem report.
  • Provide Support to COBRAG post-processing Code CABALT and participate in the level 2 processes. This included testing, documentation and verification.
  • Successfully implemented and tested Transient capability in the subchannel code COBRA.

COBRAG Application:

Provided Support to COBRAG users for its application to fuel design improvement and other special projects. This included:

  • The use of COBRG02P to limit the testing on the most suitable 5x5 configuration with cold rods that can best simulates steam vent around the water rod. The results were used for design optimization of the GNF3 bundle. 
  • Analyzing the mal distribution of the sub-channel flow of GNF2 and GE14 fuel bundles. The results were used to improve the design of the GNF3 bundle.
  • COBRAG simulation of a variety of part length rod locations for wide range of mass flux to determine the optimum design (better flow distribution) of the Gnf3 design.

Development of Core Simulator Thermal hydraulics (AETNA):

  • Responsible engineer for the thermal hydraulic model review, enhancement, testing and deployment of the BWR Core Simulator (AETNA).
  • Participated in reviewing and revising AETNA level one documentations (HSSS, SMP). Established AETNA thermal hydraulic software requirements (SRD).
  • Assessed the adequacy, improved and implement several Models in AETNA. This included Prime, Niter 24, Single channel T.H, non Ge water rod, code convergence, void fraction effect on pin power, bypass modeling options, heat transfer, self-identified and corrected several flaws. Peer reviewed T.H code changes and implementation of some iscore functionality, Gesam and P11 errors correction and enhancement.
  • Reviewed and revised AETNA MDD and STP related to the TH. solution. Established scientifically demonstrated validation process for AETNA TH. Through expanding its test matrix using experimental data for pressure drop and void fraction which will provide sufficient of the predictive capabilities.

Dryout Model (GEXL) Development and Deployment:

  • Designed, tested and delivered two GEXLMODULES on x32 and x64 Platforms along with the required documentations STP, STR and Interface Specification. Manage to involve customer in the preliminary testing, which helped reducing handover time of two MODULES to half time of  delivering one module.


Other Publications

[1] B. Hizoum, D. Miranda, K. Kang, S. Oh, J.G.M. Andersen, S. Bowman, “Transient Subchannel Analysis of BWR Fuel Thermal Hydraulic Performance”, The 19th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, NURETH-18, Portland, OR, August 18, 2019
[2] S. Oh*, B. Hizoum, P. Saha, B. Dooies, D. Miranda, “Film-droplet split model at the onset of annular-mist”, the 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (Nureth (16)\
[3] B. Hizoum, P. Saha, J. G. M. Andersen and K. Whitlow, “Droplet Entrainment and Deposition rate Models for Determination of Boiling Transition in BWR Fuel Assembly”, NURETH-14-387, September 2011.
[4] B. Hizoum, Jens Andersen, Asuka Sakoda, Scott Bowman, COBRG Subchannel Analysis of BWR fuel thermal Hydraulic Performance, Proceedings of 2010 LWR Fuel Performance/TopFuel/WRFPM, September 2010.
[5] Martin J Guillot and Belgacem Hizoum, “Application of a Discontinuous Galerkin Method to the 1-D Shallow Water Equations”, ASCE Manuscript number: HY/2002/023043, journal of Hydraulic
[6] S. Oh, B. Hizoum, K. Kang, D. Miranda, J. Andersen, S. Bowman, “Application of the COBRAG Subchannel Code to Fuel Design,” 18th Int. Topical Meeting on Nuclear Reactor Thermal Hydraulics, Portland, Oregon, USA (2019). Engineering.