Multi-physics coupling Application on TRIGA reactor
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Transcript of Multi-physics coupling Application on TRIGA reactor
Multi-physics couplingApplication on TRIGA reactor
Student Romain HenrySupervisors: Prof. Dr. IZTOK TISELJ
Dr. LUKA SNOJ
PhD Topic presentation27/03/2012
FMF LJUBLJANA1
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A nuclear reactor is a “boiler” in which heat is produced the fission of some nuclei of atoms having high atomic mass
Reactor principle (1/3)
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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
Reactor principle (2/3)
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Thermal reactor: PWR,BWR Fast reactor: SFR,LFR,GFR
Reactor principle (3/3)
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Pool reactor
thermal spectrum
Water cooled
Pmax=250 kW
TRIGA
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The multiplication factor k describes the evolution of the neutron density between 2 generations
k < 1 : The neutron density decreasesThe power decreasesThe reactor is sub-critical
k = 1 : The neutron density is constantThe reactor is critical
k > 1 : The neutron density increasesThe power increasesThe reactor is super-critical
Neutron physics (1/5)
i
i
nnk 1
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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):
Neutron physics (2/5)
sat
t
iiP
N
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Natural U: 99.3% of U238 +0.7% of U235
Fuel Enriched in U235
Neutron physics (3/5)
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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
Neutron physics (4/5)
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Transport equation :
Core modeling geometry (2D, 3D), isotopic composition (fuel, moderator, …)
Neutron physics (5/5)
),,(),,(),(),,(),(),,(.),,( ''''3 tvrstvrnvvrvvdtvrnvrvtvrnvttvrn
s
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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
Thermal-hydraulics (1/3)
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Navier-Stokes system for incompressible flow with constant Newtonian properties:
◦ Continuity equation
◦ Momentum equation
◦ Energy equation
Fluid velocity Thermal diffusivity
Thermal-hydraulics (2/3)
TuTtT
Puuutu
u
2
2
).(
1).(
0.
)( coolantfuelfissionfuel
p TThPdtdT
mc pc
u
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Example of CFD result
Thermal-hydraulics (3/3)
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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)
Coupling (1/4)
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Coupling (2/4)
Neutronics Thermal-Hydraulics
Tfuel,Tmod
…
Power distribution
…
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Build a neutroniccore model accurate
Full 3D description
3D single phase flowdescription phenomena
2 codes working as 1
Coupling (3/4)
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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
Coupling (4/4)
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Basic example (1/4)
Temperature
reactivity Number of neutron
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Reactivity ρ= (k-1)/k
Temperature increases
Absorption increases
Reactivity decreases
Basic example (2/4)
20 30 40 50 60 70 80 90 100 110
-10-9-8-7-6-5-4-3-2-10
measurement
T(°C)
Δρ/ΔT(pcm/°C)
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Point kinetic (Boltzmann with no space dependence)
C precursorλ decay constant
l Neutron lifetimein critical reactor
β proportion ofdelayed neutron
Thermodynamic law
Basic example (3/4)
iiii
ii
i
Cnldt
dC
Cnldt
dn
)()( coolantfuelfissionfuel
p TTnPdtdT
mc
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Basic example (4/4)
Temperature
reactivity Number of neutron
Δρ/ΔT
Point kinetic
Pfission
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Build a full 3D model of the TRIGA reactor Simpler geometry Data easily available
See which application we can have for a power reactor
Conclusion
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Thank you for your attention