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JoffreyDorvillepaulromano
JoffreyDorville
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paulromano
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Kinetics parameters using Iterated Fission Probability (#3133)
Co-authored-by: Paul Romano <paul.k.romano@gmail.com>
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‎CMakeLists.txt‎

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@@ -343,6 +343,7 @@ list(APPEND libopenmc_SOURCES
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src/geometry.cpp
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src/geometry_aux.cpp
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src/hdf5_interface.cpp
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src/ifp.cpp
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src/initialize.cpp
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src/lattice.cpp
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src/material.cpp

‎docs/source/usersguide/index.rst‎

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@@ -22,6 +22,7 @@ essential aspects of using OpenMC to perform simulations.
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plots
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depletion
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decay_sources
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kinetics
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scripts
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processing
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parallel

‎docs/source/usersguide/kinetics.rst‎

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.. _kinetics:
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===================
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Kinetics parameters
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===================
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OpenMC has the capability to estimate the following adjoint-weighted effective
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generation time :math:`\Lambda_{\text{eff}}` and the effective delayed neutron
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fraction :math:`\beta_{\text{eff}}`. These parameters are calculated using the
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iterated fission probability (IFP) method [Hurwitz_1964]_ based on a similar
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approach as in `Serpent 2 <https://doi.org/10.1016/j.anucene.2013.10.032>`_. The
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implementation in OpenMC is limited to eigenvalue calculations and is described
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in more details in [Dorville_2025]_.
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----------------------------------
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Iterated Fission Probability (IFP)
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----------------------------------
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With IFP, additional information needs to be recorded during the simulation
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compared to a typical eigenvalue calculation. OpenMC stores an additional
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set of values (neutron lifetime or delayed neutron group number for
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:math:`\Lambda_{\text{eff}}` or :math:`\beta_{\text{eff}}`, respectively)
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for every fission neutron simulated. Each set of values corresponds to
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the values that are associated to the :math:`N_{\text{gen}}` direct ancestors
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of any given fission neutron.
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:math:`N_{\text{gen}}` is referred to as the number of generations in the
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IFP method and corresponds to the number of generations between the birth of
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a fission neutron and the time its score is added to the IFP tally. By default,
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OpenMC considers 10 generations but this value can be modified by the user via
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the ``ifp_n_generation`` settings in the Python API::
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settings.ifp_n_generation = 5
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``ifp_n_generation`` should be greater than 0, but should also be lower than
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or equal to the number of inactive batches declared for the calculation.
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The respect of these constraints is verified by OpenMC before any calculation.
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OpenMC will automatically detect the type of data that needs to be stored based
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on the tally scores selected by the user. This guarantees that only information
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of interest are stored during a simulation and avoids using extra memory when
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only one parameter is needed. The following table shows the tally scores that
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are needed to compute kinetics parameters in OpenMC:
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.. table:: **OpenMC tally scores needed to calculate adjoint-weighted kinetics parameters**
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:align: center
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=============================== ============================ ========================== ========
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OpenMC tally score \\ Parameter :math:`\Lambda_{\text{eff}}` :math:`\beta_{\text{eff}}` Both
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=============================== ============================ ========================== ========
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``ifp-time-numerator`` X X
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``ifp-beta-numerator`` X X
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``ifp-denominator`` X X X
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=============================== ============================ ========================== ========
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|
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.. note:: Because the memory footprint of additional data is generally non-negligible
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with IFP, it is recommended to choose the value for ``ifp_n_generation`` carefully.
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For example, using one generation for both kinetics parameters corresponds to store
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one additional integer (for the delayed neutron group number used with
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:math:`\beta_{\text{eff}}`) and one floating point value (for the neutron lifetime
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used with :math:`\Lambda_{\text{eff}}`) for every fission neutron simulated once the
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asymptotic regime is reached.
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-----------------------------
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Obtaining kinetics parameters
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-----------------------------
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Here is an example showing how to declare the three available IFP scores in a
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single tally::
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tally = openmc.Tally(name="ifp-scores")
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tally.scores = [
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"ifp-time-numerator",
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"ifp-beta-numerator",
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"ifp-denominator"
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]
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The effective generation time :math:`\Lambda_{\text{eff}}` is calculated
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by dividing the result of the ``ifp-time-numerator`` score by the one obtained
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for ``ifp-denominator`` and by the :math:`k_{\text{eff}}` of the simulation:
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.. math::
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:label: lambda_eff
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\Lambda_{\text{eff}} = \frac{S_{\text{ifp-time-numerator}}}{S_{\text{ifp-denominator}} \times k_{\text{eff}}}
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The effective delayed neutron fraction :math:`\beta_{\text{eff}}` is calculated
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by dividing the result of the ``ifp-beta-numerator`` score by the one obtained
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for ``ifp-denominator``:
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.. math::
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:label: beta_eff
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\beta_{\text{eff}} = \frac{S_{\text{ifp-beta-numerator}}}{S_{\text{ifp-denominator}}}
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.. only:: html
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.. rubric:: References
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.. [Hurwitz_1964] H. Hurwitz Jr., "Naval Reactors Physics Handbook", volume 1, p. 864.
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Radkowsky, A. (Ed.), Naval Reactors, Division of Reactor Development, U.S.
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Atomic Energy Commission (1964).
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.. [Dorville_2025] J. Dorville, L. Labrie-Cleary, and P. K. Romano, "Implementation
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of the Iterated Fission Probability Method in OpenMC to Compute Adjoint-Weighted
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Kinetics Parameters", International Conference on Mathematics and Computational
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Methods Applied to Nuclear Science and Engineering (M&C 2025), Denver, April 27-30,
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2025 (to be presented).

‎docs/source/usersguide/tallies.rst‎

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| |particle. Note that this score can only be combined|
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| |with a cell filter and an energy filter. |
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+----------------------+---------------------------------------------------+
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|ifp-time-numerator |Adjoint-weighted lifetime of neutron produced by |
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| |fission in units of seconds per source particle. |
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| |This score is used to compute kinetics parameters |
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| |using the iterated fission probability (IFP) |
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| |method. |
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+----------------------+---------------------------------------------------+
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|ifp-beta-numerator |Adjoint-weighted number of delayed fission events |
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| |in units of number of delayed fission event per |
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| |source particle. This score is used to compute |
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| |kinetics parameters using the iterated fission |
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| |probability (IFP) method. |
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+----------------------+---------------------------------------------------+
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|ifp-denominator |Weights corresponding to the number of fission |
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| |events in units of number of fission event per |
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| |source particle. This score is used to compute |
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| |kinetics parameters using the iterated fission |
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| |probability (IFP) method. |
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+----------------------+---------------------------------------------------+
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.. _usersguide_tally_normalization:
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‎include/openmc/bank.h‎

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extern SharedArray<SourceSite> fission_bank;
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extern vector<vector<int>> ifp_source_delayed_group_bank;
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extern vector<vector<double>> ifp_source_lifetime_bank;
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extern vector<vector<int>> ifp_fission_delayed_group_bank;
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extern vector<vector<double>> ifp_fission_lifetime_bank;
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extern vector<int64_t> progeny_per_particle;
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} // namespace simulation

‎include/openmc/constants.h‎

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SCORE_FISS_Q_PROMPT = -14, // prompt fission Q-value
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SCORE_FISS_Q_RECOV = -15, // recoverable fission Q-value
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SCORE_DECAY_RATE = -16, // delayed neutron precursor decay rate
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SCORE_PULSE_HEIGHT = -17 // pulse-height
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SCORE_PULSE_HEIGHT = -17, // pulse-height
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SCORE_IFP_TIME_NUM = -18, // IFP lifetime numerator
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SCORE_IFP_BETA_NUM = -19, // IFP delayed fraction numerator
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SCORE_IFP_DENOM = -20 // IFP common denominator
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};
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// Global tally parameters
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// Miscellaneous
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constexpr int C_NONE {-1};
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// Default value of generation for IFP
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constexpr int DEFAULT_IFP_N_GENERATION {10};
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// Interpolation rules
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enum class Interpolation {
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histogram = 1,

‎include/openmc/ifp.h‎

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#ifndef OPENMC_IFP_H
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#define OPENMC_IFP_H
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#include "openmc/message_passing.h"
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#include "openmc/particle.h"
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#include "openmc/particle_data.h"
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#include "openmc/settings.h"
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namespace openmc {
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//! Check the value of the IFP parameter for beta effective or both.
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//!
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//! \return true if "BetaEffective" or "Both", false otherwise.
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bool is_beta_effective_or_both();
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//! Check the value of the IFP parameter for generation time or both.
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//!
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//! \return true if "GenerationTime" or "Both", false otherwise.
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bool is_generation_time_or_both();
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//! Resize IFP vectors
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//!
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//! \param[in,out] delayed_groups List of delayed group numbers
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//! \param[in,out] lifetimes List of lifetimes
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//! \param[in] n Dimension to resize vectors
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template<typename T, typename U>
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void resize_ifp_data(vector<T>& delayed_groups, vector<U>& lifetimes, int64_t n)
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{
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if (is_beta_effective_or_both()) {
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delayed_groups.resize(n);
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}
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if (is_generation_time_or_both()) {
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lifetimes.resize(n);
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}
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}
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//! Update a list of values by adding a new value if the size
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//! of the list can accomodate the new value or by shifting all
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//! values to the left (removing the first value of the list
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//! and adding the new value at the end of the list).
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//!
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//! \param[in] value Value to add to the list
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//! \param[in] data Initial version of the list
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//! \return Updated list
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template<typename T>
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vector<T> _ifp(const T& value, const vector<T>& data)
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{
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vector<T> updated;
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size_t source_idx = data.size();
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if (source_idx < settings::ifp_n_generation) {
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updated.resize(source_idx + 1);
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for (size_t i = 0; i < source_idx; i++) {
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updated[i] = data[i];
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}
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updated[source_idx] = value;
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} else if (source_idx == settings::ifp_n_generation) {
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updated.resize(source_idx);
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for (size_t i = 0; i < source_idx - 1; i++) {
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updated[i] = data[i + 1];
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}
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updated[source_idx - 1] = value;
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}
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return updated;
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}
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//! \brief Iterated Fission Probability (IFP) method.
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//!
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//! Add the IFP information in the IFP banks using the same index
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//! as the one used to append the fission site to the fission bank.
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//! Multithreading protection is guaranteed by the index returned by the
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//! thread_safe_append call in physics.cpp.
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//!
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//! Needs to be done after the delayed group is found.
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//!
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//! \param[in] p Particle
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//! \param[in] site Fission site
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//! \param[in] idx Bank index from the thread_safe_append call in physics.cpp
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void ifp(const Particle& p, const SourceSite& site, int64_t idx);
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//! Resize the IFP banks used in the simulation
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void resize_simulation_ifp_banks();
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//! Retrieve IFP data from the IFP fission banks.
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//!
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//! \param[in] i_bank Index in the fission banks
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//! \param[in,out] delayed_groups Delayed group numbers
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//! \param[in,out] lifetimes Lifetimes lists
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void copy_ifp_data_from_fission_banks(
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int i_bank, vector<int>& delayed_groups, vector<double>& lifetimes);
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#ifdef OPENMC_MPI
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//! Deserialization information for transfer of IFP data using MPI
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struct DeserializationInfo {
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int64_t index_local; //!< local index
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int64_t n; //!< number of sites sent
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};
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//! Broadcast the number of generation determined by the size of the first
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//! element on the first processor.
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//!
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//! \param[in] n_generation Number of generations
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//! \param[in] delayed_groups List of delayed group numbers lists
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//! \param[in] lifetimes List of lifetimes lists
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void broadcast_ifp_n_generation(int& n_generation,
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const vector<vector<int>>& delayed_groups,
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const vector<vector<double>>& lifetimes);
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//! Send IFP data using MPI.
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//!
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//! \param[in] idx Index of the first site
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//! \param[in] n Number of sites to send
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//! \param[in] n_generation Number of generations
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//! \param[in] neighbor Index of the neighboring processor
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//! \param[in] requests MPI requests
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//! \param[in] delayed_groups List of delayed group numbers lists
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//! \param[out] send_delayed_groups Delayed group numbers buffer
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//! \param[in] lifetimes List of lifetimes lists
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//! \param[out] send_lifetimes Lifetimes buffer
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void send_ifp_info(int64_t idx, int64_t n, int n_generation, int neighbor,
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vector<MPI_Request>& requests, const vector<vector<int>>& delayed_groups,
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vector<int>& send_delayed_groups, const vector<vector<double>>& lifetimes,
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vector<double>& send_lifetimes);
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//! Receive IFP data using MPI.
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//!
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//! \param[in] idx Index of the first site
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//! \param[in] n Number of sites to receive
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//! \param[in] n_generation Number of generations
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//! \param[in] neighbor Index of the neighboring processor
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//! \param[in] requests MPI requests
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//! \param[in] delayed_groups List of delayed group numbers
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//! \param[in] lifetimes List of lifetimes
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//! \param[out] deserialization Information to deserialize the received data
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void receive_ifp_data(int64_t idx, int64_t n, int n_generation, int neighbor,
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vector<MPI_Request>& requests, vector<int>& delayed_groups,
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vector<double>& lifetimes, vector<DeserializationInfo>& deserialization);
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//! Copy partial IFP data from local lists to source banks.
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//!
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//! \param[in] idx Index of the first site
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//! \param[in] n Number of sites to copy
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//! \param[in] i_bank Index in the IFP source banks
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//! \param[in] delayed_groups List of delayed group numbers lists
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//! \param[in] lifetimes List of lifetimes lists
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void copy_partial_ifp_data_to_source_banks(int64_t idx, int n, int64_t i_bank,
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const vector<vector<int>>& delayed_groups,
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const vector<vector<double>>& lifetimes);
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//! Deserialize IFP information received using MPI and store it in
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//! the IFP source banks.
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//!
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//! \param[in] n_generation Number of generations
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//! \param[out] deserialization Information to deserialize the received data
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//! \param[in] delayed_groups List of delayed group numbers
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//! \param[in] lifetimes List of lifetimes
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void deserialize_ifp_info(int n_generation,
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const vector<DeserializationInfo>& deserialization,
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const vector<int>& delayed_groups, const vector<double>& lifetimes);
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#endif
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//! Copy IFP temporary vectors to source banks.
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//!
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//! \param[in] delayed_groups List of delayed group numbers lists
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//! \param[in] lifetimes List of lifetimes lists
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void copy_complete_ifp_data_to_source_banks(
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const vector<vector<int>>& delayed_groups,
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const vector<vector<double>>& lifetimes);
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//! Allocate temporary vectors for IFP data.
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//!
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//! \param[in,out] delayed_groups List of delayed group numbers lists
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//! \param[in,out] lifetimes List of delayed group numbers lists
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void allocate_temporary_vector_ifp(
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vector<vector<int>>& delayed_groups, vector<vector<double>>& lifetimes);
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//! Copy local IFP data to IFP fission banks.
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//!
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//! \param[in] delayed_groups_ptr Pointer to delayed group numbers
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//! \param[in] lifetimes_ptr Pointer to lifetimes
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void copy_ifp_data_to_fission_banks(
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const vector<int>* delayed_groups_ptr, const vector<double>* lifetimes_ptr);
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} // namespace openmc
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#endif // OPENMC_IFP_H

‎include/openmc/particle_data.h‎

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int cell_born_ {-1};
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// Iterated Fission Probability
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double lifetime_ {0.0}; //!< neutron lifetime [s]
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int n_collision_ {0};
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bool write_track_ {false};
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double& time_last() { return time_last_; }
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const double& time_last() const { return time_last_; }
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// Particle lifetime
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double& lifetime() { return lifetime_; }
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const double& lifetime() const { return lifetime_; }
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// What event took place, described in greater detail below
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TallyEvent& event() { return event_; }
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const TallyEvent& event() const { return event_; }

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