openmc.deplete – Depletion

Primary API

The two primary requirements to perform depletion with openmc.deplete are:

  1. A transport operator

  2. A time-integration scheme

The former is responsible for executing a transport code, like OpenMC, and retaining important information required for depletion. The most common examples are reaction rates and power normalization data. The latter is responsible for projecting reaction rates and compositions forward in calendar time across some step size \(\Delta t\), and obtaining new compositions given a power or power density. The Operator is provided to handle communicating with OpenMC. Several classes are provided that implement different time-integration algorithms for depletion calculations, which are described in detail in Colin Josey’s thesis, Development and analysis of high order neutron transport-depletion coupling algorithms.

PredictorIntegrator

Deplete using a first-order predictor algorithm.

CECMIntegrator

Deplete using the CE/CM algorithm.

CELIIntegrator

Deplete using the CE/LI CFQ4 algorithm.

CF4Integrator

Deplete using the CF4 algorithm.

EPCRK4Integrator

Deplete using the EPC-RK4 algorithm.

LEQIIntegrator

Deplete using the LE/QI CFQ4 algorithm.

SICELIIntegrator

Deplete using the SI-CE/LI CFQ4 algorithm.

SILEQIIntegrator

Deplete using the SI-LE/QI CFQ4 algorithm.

Each of these classes expects a “transport operator” to be passed. An operator specific to OpenMC is available using the following class:

Operator

OpenMC transport operator for depletion.

The Operator must also have some knowledge of how nuclides transmute and decay. This is handled by the Chain.

Minimal Example

A minimal example for performing depletion would be:

>>> import openmc
>>> import openmc.deplete
>>> geometry = openmc.Geometry.from_xml()
>>> settings = openmc.Settings.from_xml()

# Representation of a depletion chain
>>> chain_file = "chain_casl.xml"
>>> operator = openmc.deplete.Operator(
...     geometry, settings, chain_file)

# Set up 5 time steps of one day each
>>> dt = [24 * 60 * 60] * 5
>>> power = 1e6  # constant power of 1 MW

# Deplete using mid-point predictor-corrector
>>> cecm = openmc.deplete.CECMIntegrator(
...     operator, dt, power)
>>> cecm.integrate()

Internal Classes and Functions

When running in parallel using mpi4py, the MPI intercommunicator used can be changed by modifying the following module variable. If it is not explicitly modified, it defaults to mpi4py.MPI.COMM_WORLD.

openmc.deplete.comm

MPI intercommunicator used to call OpenMC library

Type

mpi4py.MPI.Comm

During a depletion calculation, the depletion chain, reaction rates, and number densities are managed through a series of internal classes that are not normally visible to a user. However, should you find yourself wondering about these classes (e.g., if you want to know what decay modes or reactions are present in a depletion chain), they are documented here. The following classes store data for a depletion chain:

Chain

Full representation of a depletion chain.

DecayTuple

Decay mode information

Nuclide

Decay modes, reactions, and fission yields for a single nuclide.

ReactionTuple

Transmutation reaction information

FissionYieldDistribution

Energy-dependent fission product yields for a single nuclide

FissionYield

Mapping for fission yields of a parent at a specific energy

The Chain class uses information from the following module variable:

chain.REACTIONS

Dictionary that maps transmutation reaction names to information needed when a chain is being generated: MT values, the change in atomic/mass numbers resulting from the reaction, and what secondaries are produced.

Type

dict

The following classes are used during a depletion simulation and store auxiliary data, such as number densities and reaction rates for each material.

AtomNumber

Stores local material compositions (atoms of each nuclide).

OperatorResult

Result of applying transport operator

ReactionRates

Reaction rates resulting from a transport operator call

Results

Results from a depletion simulation

StepResult

Result of a single depletion timestep

The following class and functions are used to solve the depletion equations, with cram.CRAM48() being the default.

cram.IPFCramSolver

CRAM depletion solver that uses incomplete partial factorization

cram.CRAM16

Solve depletion equations using IPF CRAM

cram.CRAM48

Solve depletion equations using IPF CRAM

pool.deplete

Deplete materials using given reaction rates for a specified time

pool.USE_MULTIPROCESSING

Boolean switch to enable or disable the use of multiprocessing when solving the Bateman equations. The default is to use multiprocessing, but can cause the simulation to hang in some computing environments, namely due to MPI and networking restrictions. Disabling this option will result in only a single CPU core being used for depletion.

Type

bool

pool.NUM_PROCESSES

Number of worker processes used for depletion calculations, which rely on the multiprocessing.pool.Pool class. If set to None (default), the number returned by os.cpu_count() is used.

The following classes are used to help the openmc.deplete.Operator compute quantities like effective fission yields, reaction rates, and total system energy.

helpers.AveragedFissionYieldHelper

Class that computes fission yields based on average fission energy

helpers.ChainFissionHelper

Computes normalization using fission Q values from depletion chain

helpers.ConstantFissionYieldHelper

Class that uses a single set of fission yields on each isotope

helpers.DirectReactionRateHelper

Class for generating one-group reaction rates with direct tallies

helpers.EnergyScoreHelper

Class responsible for obtaining system energy via a tally score

helpers.FissionYieldCutoffHelper

Helper that computes fission yields based on a cutoff energy

helpers.FluxCollapseHelper

Class that generates one-group reaction rates using multigroup flux

Abstract Base Classes

A good starting point for extending capabilities in openmc.deplete is to examine the following abstract base classes. Custom classes can inherit from abc.TransportOperator to implement alternative schemes for collecting reaction rates and other data from a transport code prior to depleting materials

abc.TransportOperator

Abstract class defining a transport operator

The following classes are abstract classes used to pass information from OpenMC simulations back on to the abc.TransportOperator

abc.NormalizationHelper

Abstract class for obtaining normalization factor on tallies

abc.FissionYieldHelper

Abstract class for processing energy dependent fission yields

abc.ReactionRateHelper

Abstract class for generating reaction rates for operators

Custom integrators or depletion solvers can be developed by subclassing from the following abstract base classes:

abc.Integrator

Abstract class for solving the time-integration for depletion

abc.SIIntegrator

Abstract class for the Stochastic Implicit Euler integrators

abc.DepSystemSolver

Abstract class for solving depletion equations