Current Status and On-Going Development of VTT’s Kraken Core Physics Computational Framework

Jaakko Leppänen (Corresponding Author), Ville Valtavirta, Antti Rintala, Ville Hovi, Riku Tuominen, Jussi Peltonen, Markus Hirvensalo, Eric Dorval, Unna Lauranto, Rebekka Komu

Research output: Contribution to journalArticleScientificpeer-review

6 Citations (Scopus)


The Kraken computational framework is a new modular calculation system designed for coupled core physics calculations. The development started at VTT Technical Research Centre of Finland in 2017, with the aim to replace VTT’s outdated legacy codes used for the deterministic safety analyses of Finnish power reactors. In addition to conventional large PWRs and BWRs, Kraken is intended to be used for the modeling of SMRs and emerging non-LWR technologies. The main computational modules include the Serpent Monte Carlo neutron and photon transport code, the Ants nodal neutronics solver, the FINIX fuel behavior module and the Kharon thermal hydraulics code, all developed at VTT. The core physics solution can be further coupled to system-scale simulations. In addition to development, significant effort has been devoted to verification and validation of the implemented methodologies. The reduced-order Ants code has been successfully used for steady-state, transient and burnup simulations of PWRs with rectangular and hexagonal core geometry. The Ants–Kharon–FINIX code sequence is actively used for the core design tasks in VTT’s district heating reactor project. This paper is a general overview on the background, functional description, current status and future plans for the Kraken framework. Due to the short history of development, Kraken has not yet been comprehensively validated or applied to full-scale core physics calculations. A review of previous studies is instead provided to exemplify the practical use.
Original languageEnglish
Article number876
Issue number3
Publication statusPublished - 25 Jan 2022
MoE publication typeA1 Journal article-refereed


  • core physics
  • coupled simulation
  • neutronics
  • thermal hydraulics
  • fuel behavior
  • Kraken
  • Serpent
  • Ants
  • Kharon
  • Neutronics
  • Fuel behavior
  • Core physics
  • Thermal hydraulics
  • Coupled simulation


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