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Reactor Models for Embalse NPP


Develop reactor physics model of Embalse for use in safety analyses.


As part of the CANDU-6 Embalse refurbishment, most of safety analyses must be performed using the latest safety codes and methodologies.  The reactor core model must be updated to a full 2-group model, including all updated structure material and reactivity mechanisms. 

Specific operation features of Embalse nuclear plant compared to other C6 are the use of Gadolinium as only moderator poison and the use of Cobalt adjuster rods.  For the pre-equilibrium and equilibrium safety analyses, the reactor core models for the different steps of life cycle are performed.  Moreover to allow flexibility in reactor outage frequency, cobalt adjusters were assessed irradiated using ORIGEN-S in core for 18 months irradiation, and their properties updated as a result.The work consists of identifying dimensions and isotopic compositions of all structural materials and reactivity devices, to model them in 3D within DRAGON, and to integrate them into RFSP core models.  

In total, three core models have been developed to represent the reactor life time (fresh core, plutonium peak core, and 20-year crept time-average core).  An additional uncrept core model including irradiated cobalt adjuster rods has been developed.

​The objectives of the work were also to determine the reactivity coefficients for fuel temperature, coolant density and coolant temperature to be used in point kinetics model within thermohydraulics code for safety analyses (e.g. CATHENA).

The work was contracted by NA-SA, Argentina to Candu Energy inc.  Dr Elisabeth Varin was the technical lead. She supervised the work performed in Montréal and in Mississauga

NOTE:  This work was performed / lead by MNS personnel during their previous employment


  • DRAGON models for cobalt adjuster rods (one to four Cobalt pins), and for structural materials,

  • RFSP core model for fresh core, including depleted bundles, RFSP core model for crept time-average conditions,

  • Irradiation calculation of Cobalt adjuster rods composition and properties using DRAGON, RFSP and ORIGEN-S

  • Model report including description of all structural material and reactivity mechanisms, creep information after 20 years, SCM fuel table description for crept and fresh fuel bundles (natural and depleted uranium composition), RFSP models showing channel power distributions, and kinetics parameters for each core model

  • Reactivity coefficients for each core model for fuel temperature, coolant density and coolant temperature to be used in trip coverage analysis

  • Technical note to document irradiation calculation and new properties of cobalt adjuster rods


  • Incremental Cross-sections
  • SCM Fuel Model
  • Neutronics
  • Kinetics Information



Embalse, Argentina 



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