Mutiphysics coupling
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Transcript Mutiphysics coupling
Multi-physics coupling
Application on TRIGA reactor
Student
Supervisors:
Romain Henry
Prof. Dr. IZTOK TISELJ
Dr. LUKA SNOJ
PhD Topic presentation
27/03/2012
FMF LJUBLJANA
1
A nuclear reactor is a “boiler” in which heat is
produced the fission of some nuclei of atoms
having high atomic mass
2
fission products
radioactive
2 to 3 prompt neutrons
High energy photons
The reaction is exo-energetic (~ 200 MeV)
1 fission produce 10^8 times more energy that
burning one atom of carbon
delayed neutrons are emitted
a chain reaction is possible
3
Thermal reactor: PWR,BWR
Fast reactor: SFR,LFR,GFR
4
Pool reactor
thermal spectrum
Water cooled
Pmax=250 kW
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
ni 1
k
ni
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Interaction neutron matter :
Notion of cross section (expressed in barns)
Absorption (fission, capture), scattering
Total cross section:
interaction probability :
t
a
s
P
i
i
t
macroscopic cross section
for a given material (atoms density N):
N
7
Natural U: 99.3% of U238 +0.7% of U235
Fuel Enriched in U235
8
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
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Transport equation :
n(r , v , t )
v .n(r , v , t ) v (r , v )n(r , v , t ) d 3v 'v ' s (r , v ' v )n(r , v ' , t ) s(r , v , t )
t
Core modeling geometry (2D, 3D), isotopic
composition (fuel, moderator, …)
10
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
11
Navier-Stokes system for incompressible flow
with constant Newtonian properties:
◦ Continuity equation
◦ Momentum equation
.u 0
u
1
.(u u ) 2 u
P
t
T
.(Tu ) 2T
t
◦ Energy equation
u
Fluid velocity
Thermal diffusivity
c p
m cp
dTfuel
dt
Pfission h(T fuel Tcoolant )
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Example of
CFD result
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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)
14
Tfuel,
Tmod
…
ThermalHydraulics
Neutronics
Power
distribution
…
15
Build a neutronic
core model accurate
Full 3D description
3D single phase flow
description phenomena
2 codes working as 1
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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
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Temperature
reactivity
Number of
neutron
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Reactivity ρ= (k-1)/k
Temperature increases
0
Absorption increases
-1 0
-2
20
40
60
80
100 T(°C) 120
Δρ/ΔT(pcm/°C)
-3
-4
Reactivity decreases
-5
-6
measurement
-7
-8
-9
-10
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Point kinetic (Boltzmann with no space
dependence)
dn
n i Ci
dt
l
i
C precursor
λ decay constant
l Neutron lifetime
in critical reactor
β proportion of
delayed neutron
Thermodynamic law m cp
dCi i
n i Ci
dt
l
dTfuel
dt
Pfission (n) (T fuel Tcoolant )
20
Temperature
Δρ/ΔT
reactivity
Pfission
Point
kinetic
Number of
neutron
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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
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Thank you for
your attention
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