INSTANT/PHISICS – RELAP5 coupling
A. Epiney, C. Rabiti, Y. Wang, J. Cogliati, T. Grimmett, P. Palmiotti
Overview
• Adding the PHISICS tool suite to RELAP5-3D– A new transport/diffusion solver: INSTANT– A New cross section model: XS-MIXER
• Examples– Typical PWR– Takeda 4 benchmark– NGNP MHTGR
• Summary and outlook
Vision
Increase of neutronics modeling accuracyModeling flexibilityUncertainty assessment
PHISICSRELAP5-3D
Lean software inter-dependencyLow impact for user
RELAP5-INSTANT vs RELAP5-NESTLEFeatures RELAP5 - NESTLE RELAP5 - PHISICS
Energy group 2-4 Not bounded
Diffusion Yes Yes
Transport No Yes
Triangular Mesh No Yes
Unstructured Mesh No Yes
Adjoint No Yes
Multi-Dimensional Cross Section Tables No Yes
Speed Win Lose (Future ?)
Discontinuity Factors Yes Future ?
Cylindrical Geometry No Future
Perturbation Theory No Future
Depletion No Future
Localized refinement No Future
New transport core solver: INSTANT
• Accessible through new keyword “INSTANT”$------------------------------------------------------------
$ REACTOR KINETICS INPUT
$------------------------------------------------------------
30000000 instant gen
30000001 no-gamma 3600.0e+6 0.0076 6 1.0 0.48
…
• Compatible with RELAP5: cross section models
control rod model
Existing RELAP5 inputs will run just by changing “nodal” to “instant”
• INSTANT control parameters (if different from default) could be provided through separate input file
New cross section model PHISICS• PHISICS gives additional access to:
– Unlimited number of energy groups (memory limit)
– Transport XS vs. Diffusion Coeffs.– Square root vs. linear structure temp. FB– Simple HTML input– Different FB tabulations for different materials
• Table allows to account for cross terms• Multiple points address non linearity• Functional representation in the future
New cross section model PHISICS
• Accessible through new keyword “PHISICS”$------------------------------------------------------------
$ REACTOR KINETICS INPUT
$------------------------------------------------------------
30000000 instant phisics
30000001 no-gamma 3600.0e+6 0.0076 6 1.0 0.48
…
– Compatible with RELAP5 CR model– Kinetic nodes to TH mapping: as in “Gen”
• FB Zones and Regions for:– Structure temperature– Fluid temperature– Fluid density– Poison concentration
The “Gen” feedback structure
• Every kinetic node is assigned to a FB Zone– (Zone figures are assigned to axial meshes like
for compositions)• Every FB Zone has:
– a number of heat structure FB regions• Every HSFB region feeds back one (weighted) structure
temperature
– a number of volume FB regions• Every VFB region feeds back: (weighted) density, temperature
and poison concentration
• Total feedback variables: HSFB + 3*VFB
Implementation (using RELAP5 XS models)
RELAP 5:Plant and TH
INSTANT
XS, Geometry
Power
Compatibility with existing RELAP5 XS and control rod models
Implementation (PHISICS XS)
RELAP 5:Plant and TH
XS-MIXER
INSTANT
Tf, Tc, ρc,…CR positions
XS
Power
Steady state search using several energy group (>4) has been already implemented
GeometryControls…
Software Structure
RELAP Input Reader
Feed input
Branch to a specialinput file
RELAP/PHISICS driver
Data Type
PHISICS input file reader
Construction-destruction
Data Type
INSTANT DRIVER (pointing local data type interface)
Data TypeFeeding
RELAP5 INSTANT
Neutronics TH coupling
Cartesian Geometry: Typical PWR
• Rod in/out cases• Full core model• 17x17 nodes• 13 axial levels• 11 Materials• 36 Feedback zones• 2 Energy group
CR out
CR in
PWR Rod Out
Easy visualization with INSTANT(VTK file)
*surface order 1, volume 4
Convergence evolution
Keff
Initial Converged
INSTANT* 1.01639 1.00348
RELAP 1.01731 1.00483
Delta 0.00092 0.00135
PWR Rod Out: Keff Evolution
PWR without control rods
Series1
Series3
Series5
Series7
Series9
Series11
Series13
Series15
Series17
-6
-4
-2
0
2
4
6
8
10
12
1 2 3 4 5 6 7 89
1011
1213
1415
1617
10-12
8-10
6-8
4-6
2-4
0-2
-2-0
-4--2
-6--4
Series1
Series3
Series5
Series7
Series9
Series11
Series13
Series15
Series17
-6
-4
-2
0
2
4
6
8
10
1 2 3 4 5 6 7 89
1011
1213
1415
1617
8-10
6-8
4-6
2-4
0-2
-2-0
-4--2
-6--4
• Power distribution difference (%) NESTLE/INSTANT
First iteration
Converged
Feedbacks tend to reduce the difference in power distribution
PWR Rod Out
• Comparison Comments– Difference in keff reasonable– Difference in assembly power higher than
expected. Possible reasons:• Higher spatial resolution in INSTANT (NESTLE
mesh refinement study could confirm this)• Different implementation of vacuum BC
PWR Rod Out
• Spatial convergence and computational time– INSTANT P0
Initial conditions Converged Computational time [%]Surface order Volume order
3 4 5 60 1.01736 1.01754 1 1.01639 1.01652 2 1.01645 1.016533 1.01652
S. order Volume order 3 4 5 60 1.00407 1.004401 1.00348 1.003682 1.00361 1.003723 1.00371
S. order Volume order 3 4 5 60 100 1461 182 3282 422 6963 902
• INSTANT converges spatially
• Best computational cost – accuracy ratio for • Surface order 1, Volume order 4
PWR Rod OutComputational times INSTANT vs. NESTLE
• Spatial approximation used 4th order
37 degree of freedom by node, by energy group
Flexibility comes at less computational efficiency• We started at*:
NESTLE 175s INSTANT 13760s (S1,V4)
INSTANT factor ~80 slower• Ways of reducing the computational time
• Cross section threshold gained factor of 10• Parallelization of INSTANT how many cores you have?
*Processor time in kinetics subroutines 1500 iterations
PWR rod Out
• Neutronics inactive if DXS<tolerance Gained a factor of 10
PWR Rod Out
• Using parallelization for INSTANT Þ Scaling is almost perfect on shared memory otherwise
dependent on node to node communication speed Þ factor of 10 or more possible by average users
Þ Using both, TH skipping and parallelization
the initial factor of 80 can be compensated
The real conclusion is…
Now you can choose your trade off between accuracy and computational cost
PWR Rod Out: Multi Group Test• Cross section model test with PHISICS
– 2 groups (Diffusion coefficient / Total cross sect.)– 2 group cross sections expanded to 8 and 20
groups• Energy group i is expanded into j groups• One can show that keff does not change for
Xi,j = ai,jXi X=D, Sfis, Sabs, C
Ssgi,j->gi’j’ = ai,jai’,j’Sgi->gi’
• With some constraints: Sa = 1, a not
ai,j Sabs+sum ai,j sum ai’,j’Sgi->gi’ < 1/ (3Di,j)
PWR Rod Out (PHISCS XS)
• Test confirms functioning of PHISICS XS model and multi-dimensional interpolation
PWR Rod In
• 1 control rod inserted• XS by RELAP CR
model• Steady state calculation
Convergence evolution 2nd group
INSTANT NESTLE
Keffconverged
1.03838 1.03919
Takeda 4 benchmark
• 3D Hexagonal test• 4 energy groups• No TH feedback• Small fast sodium
cooled reactor
• NESTLE vs. INSTANT
CR In CR Out
Takeda 4 benchmark (CR Out)Volume Order
Surface Order
0 1 2 35 1.079956 1.07995 1.073507 1.07995 1.07351 1.073438 1.07344 1.07342
INSTANT Diffusion
NESTLEcoarse mesh diffusion method nodal expansion solution technique
1.10693 1.07427
INSTANT: PN1 Solution converges towards PN2ND SolutionVol 6/ Surf 1 gives best computational time/accuracy ratio
RELAP/NESTLE: coarse mesh method not appropriate,nodal expansion within 90pcm (between INSTANT Surf 0 and
1)
UNIC Diffusion keff = 1.07335
Takeda 4 benchmark (CR)Volume Order
Surface Order
0 1 2 35 0.858666 0.85876 0.852787 0.85876 0.85278 0.852418 0.85242 0.85238
INSTANT PN1
NESTLEcoarse mesh diffusion method nodal expansion solution technique
0.94793 0.85984
INSTANT: PN1 Solution converges towards PN2ND SolutionVol. 6/ Surf 0 gives best computational time/accuracy ratio
RELAP/NESTLE: Coarse mesh diffusion not appropriate; nodal expansion still off by ~800 pcm
UNIC Diffusion keff = 0.85161
MHTGR (NGNP)
for the MHTGR benchmark• Features needed by the
benchmark not supported by RELAP3D-NESTLE– Linear independent feedbacks
not good enough– 26 energy groups– Need of multiple feedback
regions (Tfuel, Tgraph) in each zone– Triangular mesh for CR location
NGNP is supporting the RELAP/INSTANT coupling
NGNP MHTGRReactor vessel
Core barrel
Coolant channels
Central reflector
Fuel blocks
Side reflector
Control rod channels
• Hexagonal geometry• Inner and outer reflector• 3 Fuel rings
• RELAP5 representation for feedback zones
NGNP MHTGR
INSTANT NESTLE
Keffconverged
1.05300 1.03080
• XS by RELAP (2G)• Steady state calculation
Convergence evolution 2nd group
INSTANT: Surf. 1/Vol. 6NESTLE: coarse mesh diffusion method
Conclusion
• RELAP5-3D – PHISICS coupling add the following feature– Spatial/angular mesh refinement– Unlimited number of energy group– Cross section tabulation– In the future: depletion, time dependent, decay
heat, adjoint sensitivity analysis• We can match computational time with higher
accuracy• We preserve compatibility with past input deck
Extra Slides
Simple HTML input
• Different tabulations for different materials
<tabulation ID="1" ND="2" N="2">
<dimension ID="T_mod_VR_1" PT="2" REF="579.75">
540 600
</dimension>
<dimension ID=“T_mod_VR_2" PT="4" REF="712.5">
650 700 750 800
</dimension>
</tabulation>
<tabulation ID="2" ND="1" N="2">
<dimension ID="T_struct_HR_1" PT="5" REF="579.75">
540 555 570 585 600
</dimension>
</tabulation>
• Different tabulations with• Different number of
dimensions and points
• One dimension for each FB variable considered
Simple HTML input<dim TabID="1" ID="T_mod_VR_1" pt="540">
<dim TabID="1" ID="ro_mod_VR_1" pt="650">
<material ID="1" NA="0" fissile="true">
<NuFissionXS> 2.62E-2 2.44E-2 </NuFissionXS>
<DCXS> 6.811648 0.933646 </DCXS>
…
</material>
<material ID="2" NA="0" fissile="false">
…
</material>
</dim>
<dim TabID="1" ID="ro_mod_VR_1" pt="800">
</dim>
</dim>
<dim TabID="1" ID="T_mod_VR_1" pt="600">
<dim TabID="1" ID="ro_mod_VR_1" pt="650">
</dim>
<dim TabID="1" ID="ro_mod_VR_1" pt="800">
</dim>
</dim>
• Dimension 1• Dimension 2
=> Full table input allows
consideration of cross terms