Advanced Neutronics: PHISICS project

C. Rabiti, Y. Wang, G. Palmiotti, A. Epiney, A. Alfonsi, H. Hiruta, J. Cogliati, T. Grimmett

What is PHISICS?

Parallel and Highly Innovative Simulation for INL Code System

• PHISICS was started two years ago• The idea behind the project is to provide state of the art

simulation capability to reactor physics designers

Key features are

Modeling flexibilityHardware/software flexibilityLong term maintainabilityUncertainty analysis

Focuses

Neutronic designFluxes, burn up, fuel cycleCore feedback to system codes

PHISICS & RELAP5 !?!?

• PHISCS was born under one constrain:

increasing accuracy should not come at the expense of user time

• How?– Take advantage of parallel computing available to

the average user– Introduce a more complete representation of the

physical phenomena

These are the reasons why we believe PHISICS is a good candidate to move RELAP5 forward

PHISICS Structure• Modular infrastructure to ensure easy upgrade of

components and maintenance. No deep interdependence of modules

Kernel

Interface Kernel

Interface

Data Type

Data Type

Data Type

Data Type

Inpu

t

Inpu

t

Driver

PHISICS-RELAP5: Coupling

RELAP 5:Plant and TH

XS-MIXER

INSTANT

Tf, Tc, ρc,…

XS

Power

BatemanSolver

Flux

Nuclide Densities

Fission Power

Time DriverDecay heat

XS Source

Following the arrow clockwise, the loop reproduces an operator split approach

Overview of the Components

• INSTANT: Transport/Diffusion Solver

• MRTAU: Bateman Solver

• Adjoint Perturbation Theory Module

• Time Dependent Driver

INSTANTIntelligent Nodal and Semistrucured Treatment for Advanced

Neutron Transport

• INSTANT is in continuous development to extend its capability

• Code is designed to take full advantage of middle to large cluster (10~1000 processors)

• Code is designed to focus on method adaptation while also mesh adaptation will be possible

INSTANT: General Features• Boundary condition

– Reflective (exact) Vacuum Periodic• Number of energy group: unlimited (memory)• Anisotropic order of the scattering: up to P33• Number of thermal groups (up-scattering): unlimited• Problem type:

– fundamental mode, forward and adjoint– Source, forward and adjoint

• Outer iteration: power iteration scheme accelerated with Chebyshev

• Inner iteration acceleration: diffusion partitioning

INSTANT: Nodal Mesh/Geometry

• INSTANT has the capability to treat (with a nodal approach) the following geometry/mesh capability

• 2/3D Cartesian• 2D triangular, Z extruded• 2D hexagonal, Z extruded

Takeda 1 Benchmark (Rod In)

PN order Keff

1 (diffusion) 0.93238

3 0.96117

5 0.96214

7 0.96230

Takeda 1 Benchmark (Rod In)

MHTGR 2D Triangular Geometry

Unstructured Mesh

• C5G7

INSTANT: Inner Iteration Algorithms

• INSTANT has 3 different inner iteration schemes:

• The Krylov space based solvers (CG, and GMRES), since based on a residual formulation, are suitable for multi-physics coupling using Jacobian Free Newton Krylov methods

Multi-color by axial layers

Conjugate Gradient

Generalized Minimal RESidual

• Speed• Memory

• Scalability

Parallel Implementation of INSTNAT

Number of processors

Total computing time (s)

Speed up

1 35.70 1.00

2 17.98 1.99

3 11.11 3.21

4 8.39 4.26

6 5.93 6.02

9 4.03 8.86

• 36x36 cells with quadratic shape functions used to discretize the problem• Computing time on a single desktop with P9

SN-PN Coupling• One of the middle term goals of

INSTANT is to provide the capability to use different algorithms and mesh structures in the same geometry

• The theoretical developments needed are under development in cooperation with Texas A&M University

• Implementation in the code will start in FY12

Perturbation ModuleThe tasks of the perturbation module are

• Compute the uncertainty due to cross section in– Keff– Reactivity feedbacks– Reaction rates

• Requirements– Classical perturbation theory (adjoint in fundamental

mode)– Generalized Perturbation Theory (source adjoint in critical

problems)– Cross section manipulation tools– Perturbation integral computation

Adjoint Capability

• The adjoint solution has been already implemented in INSTANT and a perturbation module is under development

• the perturbation module will provide sensitivity analysis of input parameters (cross sections) toward several figure of merit:

• Keff• Power peak • Control rod worth• Reaction rates• Etc.

Unstructured Mesh Adjoint

MRTAU: Deacy/Depletion

Multi-Reactor Transmutation Analysis Utility• This module solves the Bateman equation• Two solution methodologies are available

– Arbitrary order of Taylor development– Arbitrary Chebyshev Rational Approximation

Method order (CRAM)• CRAM is the default methodology• Comparison of CRAM and Taylor have been

performed to confirm the correct implementation of algorithms

MRTAU Test Case

• MOX (10% NpPu/HM, 50 MWD/kg) directly recycled from spent UO2 (4.2% 235U/U, 50 MWD/kg, 5 years decay storage

• CRAM 14th order• Taylor 2nd order• Depletion Burn-Up Sequence

– 100 days cool down– 100 days core– 100 days cool down

• Reference CRAM at 3000 time step (TS)• Results for few representative isotopes

100 Days Error (%)Out of range

200 Days Error (%)Out of range

300 Days Error (%)Out of range

MRTAU remarks

• The two implemented algorithms offers the needed flexibility to model either burn up and decay

• Study are on going to assess best trade of between computational time and accuracy for transient analysis using different methodologies and orders of accuracy

Time Driver

• The module is at the design stage• The algorithm is based on the same scheme

implemented in ERANOS/KIN3D• Adaptation of the original algorithms are under

study to increase speed for very short time step

• We promised it by the end of September

ConclusionPHISICS will bring a new set of capabilities to RELAP5• Pre depletion of the core• Multi group in energy• Cross section tabulation• More flexibility in the neutronic mesh• Transport• Exact decay heat and isotopic tracking

Our goal is to deliver higher accuracy without impacting usability and computational time

Seeking Your Input

Please let us know….• what more you would like to add from the

neutronics standpoint

• Why you think what we are doing is or is not beneficial to your work

Question?