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