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Multi-physics coupling Application on TRIGA reactor

Multi-physics coupling Application on TRIGA reactor. Student Romain Henry Supervisors: Prof. Dr. IZTOK TISELJ Dr. LUKA SNOJ. PhD Topic presentation 27/03/2012 FMF LJUBLJANA. Reactor principle (1/3).

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Multi-physics coupling Application on TRIGA reactor

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  1. Multi-physics couplingApplication on TRIGA reactor Student Romain Henry Supervisors: Prof. Dr. IZTOK TISELJ Dr. LUKA SNOJ PhD Topic presentation 27/03/2012 FMF LJUBLJANA

  2. Reactor principle (1/3) • A nuclear reactor is a “boiler” in which heat is produced the fission of some nuclei of atoms having high atomic mass

  3. Reactor principle (2/3) • fission products radioactive • delayed neutrons are emitted • 2 to 3 prompt neutrons • a chain reaction is possible • High energy photons • The reaction is exo-energetic (~ 200 MeV) • 1 fission produce 10^8 times more energy that burning one atom of carbon

  4. Reactor principle (3/3) • Thermal reactor: PWR,BWR Fast reactor: SFR,LFR,GFR

  5. TRIGA • Pool reactor • thermal spectrum • Water cooled • Pmax=250 kW

  6. Neutron physics (1/5) • The multiplication factor k describes the evolution of the neutron density between 2 generations • k < 1 : The neutron density decreases The power decreases The reactor is sub-critical • k = 1 : The neutron density is constant The reactor is critical • k > 1 : The neutron density increases The power increases The reactor is super-critical

  7. Neutron physics (2/5) • Interaction neutron matter :Notion of cross section (expressed in barns) • Absorption (fission, capture), scattering • Total cross section: • interaction probability : • macroscopic cross sectionfor a given material (atoms density N):

  8. Neutron physics (3/5) • Natural U: 99.3% of U238 +0.7% of U235 • Fuel Enriched in U235

  9. Neutron physics (4/5) • Moderator: • Very low atomic mass, optimal for the slowing down process • Very low cross section for capture in the thermal range of energy • high concentration of nuclei to favor the probability of neutron scattering • Water

  10. Neutron physics (5/5) • Transport equation : • Core modeling geometry (2D, 3D), isotopic composition (fuel, moderator, …)

  11. Thermal-hydraulics (1/3) • Flow phenomena for the coolant (turbulence ,heat transfer ) • Phenomena of importance in the evaluation of fuel integrity. • CFD is a branch of fluid mechanics that uses numerical methods and algorithms to solve Navier-Stokes system

  12. Thermal-hydraulics (2/3) • Navier-Stokes system for incompressible flow with constant Newtonian properties: • Continuity equation • Momentum equation • Energy equation • Fluid velocity • Thermal diffusivity

  13. Thermal-hydraulics (3/3) • Example of CFD result

  14. Coupling (1/4) • The main goal : describe some behaviors that pure neutron transport equation or pure thermal-hydraulic models are unable to do • Research in neutron physics and nuclear thermal-hydraulics require long computational time on large parallel computer • Coupled models cannot rely on the most accurate and advanced models from both disciplines(simpler models that allow performing simulations in a reasonable time)

  15. Coupling (2/4) Tfuel, Tmod … Neutronics Thermal-Hydraulics Power distribution…

  16. Coupling (3/4) • Build a neutroniccore model accurate • Full 3D description • 3D single phase flowdescription phenomena • 2 codes working as 1

  17. Coupling (4/4) • Validation of the model through measurement with TRIGA reactor: • Detectors devices allowing to measure neutron flux for different configurations of the TRIGA core to deduce the power distribution • The temperature of the moderator is also easily accessible, with thermocouple, from the reactor pool

  18. Basic example (1/4) Temperature reactivity Number of neutron

  19. Basic example (2/4) • Reactivity ρ= (k-1)/k • Temperature increases • Absorption increases • Reactivity decreases

  20. Basic example (3/4) • Point kinetic (Boltzmann with no space dependence) • C precursorλ decay constant • l Neutron lifetimein critical reactor • β proportion ofdelayed neutron • Thermodynamic law

  21. Basic example (4/4) Temperature Δρ/ΔT Pfission reactivity Number of neutron Point kinetic

  22. Conclusion • Build a full 3D model of the TRIGA reactor • Simpler geometry • Data easily available • See which application we can have for a power reactor

  23. Thank you for your attention

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