diff --git a/docs/source/methods/neutron_physics.rst b/docs/source/methods/neutron_physics.rst index fe8b8ad8500..2b797e3dbcf 100644 --- a/docs/source/methods/neutron_physics.rst +++ b/docs/source/methods/neutron_physics.rst @@ -290,7 +290,10 @@ create and store fission sites for the following generation. First, the average number of prompt and delayed neutrons must be determined to decide whether the secondary neutrons will be prompt or delayed. This is important because delayed neutrons have a markedly different spectrum from prompt neutrons, one that has a -lower average energy of emission. The total number of neutrons emitted +lower average energy of emission. Furthermore, in simulations where tracking +time of neutrons is important, we need to consider the emission time delay of +the secondary neutrons, which is dependent on the decay constant of the +delayed neutron precursor. The total number of neutrons emitted :math:`\nu_t` is given as a function of incident energy in the ENDF format. Two representations exist for :math:`\nu_t`. The first is a polynomial of order :math:`N` with coefficients :math:`c_0,c_1,\dots,c_N`. If :math:`\nu_t` has this @@ -306,8 +309,8 @@ interpolation law. The number of prompt neutrons released per fission event :math:`\nu_p` is also given as a function of incident energy and can be specified in a polynomial or tabular format. The number of delayed neutrons released per fission event :math:`\nu_d` can only be specified in a tabular -format. In practice, we only need to determine :math:`nu_t` and -:math:`nu_d`. Once these have been determined, we can calculated the delayed +format. In practice, we only need to determine :math:`\nu_t` and +:math:`\nu_d`. Once these have been determined, we can calculate the delayed neutron fraction .. math:: @@ -335,8 +338,14 @@ neutrons. Otherwise, we produce :math:`\lfloor \nu \rfloor + 1` neutrons. Then, for each fission site produced, we sample the outgoing angle and energy according to the algorithms given in :ref:`sample-angle` and :ref:`sample-energy` respectively. If the neutron is to be born delayed, then -there is an extra step of sampling a delayed neutron precursor group since they -each have an associated secondary energy distribution. +there is an extra step of sampling a delayed neutron precursor group to get the +associated secondary energy distribution and the decay constant +:math:`\lambda`, which is needed to sample the emission delay time :math:`t_d`: + +.. math:: + :label: sample-delay-time + + t_d = -\frac{\ln \xi}{\lambda}. The sampled outgoing angle and energy of fission neutrons along with the position of the collision site are stored in an array called the fission diff --git a/examples/pincell_pulsed/run_pulse.py b/examples/pincell_pulsed/run_pulse.py new file mode 100644 index 00000000000..b6a61ad3d81 --- /dev/null +++ b/examples/pincell_pulsed/run_pulse.py @@ -0,0 +1,101 @@ +import matplotlib.pyplot as plt +import numpy as np +import openmc + +############################################################################### +# Create materials for the problem + +uo2 = openmc.Material(name="UO2 fuel at 2.4% wt enrichment") +uo2.set_density("g/cm3", 10.29769) +uo2.add_element("U", 1.0, enrichment=2.4) +uo2.add_element("O", 2.0) + +helium = openmc.Material(name="Helium for gap") +helium.set_density("g/cm3", 0.001598) +helium.add_element("He", 2.4044e-4) + +zircaloy = openmc.Material(name="Zircaloy 4") +zircaloy.set_density("g/cm3", 6.55) +zircaloy.add_element("Sn", 0.014, "wo") +zircaloy.add_element("Fe", 0.00165, "wo") +zircaloy.add_element("Cr", 0.001, "wo") +zircaloy.add_element("Zr", 0.98335, "wo") + +borated_water = openmc.Material(name="Borated water") +borated_water.set_density("g/cm3", 0.740582) +borated_water.add_element("B", 2.0e-4) # 3x the original pincell +borated_water.add_element("H", 5.0e-2) +borated_water.add_element("O", 2.4e-2) +borated_water.add_s_alpha_beta("c_H_in_H2O") + +############################################################################### +# Define problem geometry + +# Create cylindrical surfaces +fuel_or = openmc.ZCylinder(r=0.39218, name="Fuel OR") +clad_ir = openmc.ZCylinder(r=0.40005, name="Clad IR") +clad_or = openmc.ZCylinder(r=0.45720, name="Clad OR") + +# Create a region represented as the inside of a rectangular prism +pitch = 1.25984 +box = openmc.model.RectangularPrism(pitch, pitch, boundary_type="reflective") + +# Create cells, mapping materials to regions +fuel = openmc.Cell(fill=uo2, region=-fuel_or) +gap = openmc.Cell(fill=helium, region=+fuel_or & -clad_ir) +clad = openmc.Cell(fill=zircaloy, region=+clad_ir & -clad_or) +water = openmc.Cell(fill=borated_water, region=+clad_or & -box) + +# Create a model and assign geometry +model = openmc.Model() +model.geometry = openmc.Geometry([fuel, gap, clad, water]) + +############################################################################### +# Define problem settings + +# Set the mode +model.settings.run_mode = "fixed source" + +# Indicate how many batches and particles to run +model.settings.batches = 10 +model.settings.particles = 10000 + +# Set time cutoff (we only care about t < 100 seconds, see tally below) +model.settings.cutoff = {"time_neutron": 100} + +# Create the neutron pulse source (by default, isotropic direction, t=0) +space = openmc.stats.Point() # At the origin (0, 0, 0) +energy = openmc.stats.delta_function(14.1e6) # At 14.1 MeV +model.settings.source = openmc.IndependentSource(space=space, energy=energy) + +############################################################################### +# Define tallies + +# Create time filter +t_grid = np.insert(np.logspace(-6, 2, 100), 0, 0.0) +time_filter = openmc.TimeFilter(t_grid) + +# Tally for total neutron density in time +density_tally = openmc.Tally(name="Density") +density_tally.filters = [time_filter] +density_tally.scores = ["inverse-velocity"] + +# Add tallies to model +model.tallies = openmc.Tallies([density_tally]) + + +# Run the model +model.run(apply_tally_results=True) + +# Bin-averaged result +density_mean = density_tally.mean.ravel() / np.diff(t_grid) + +# Plot particle density versus time +fig, ax = plt.subplots() +ax.stairs(density_mean, t_grid) +ax.set_xscale("log") +ax.set_yscale("log") +ax.set_xlabel("Time [s]") +ax.set_ylabel("Total density") +ax.grid() +plt.show() diff --git a/include/openmc/settings.h b/include/openmc/settings.h index 069d94c3b28..9a1a7a98384 100644 --- a/include/openmc/settings.h +++ b/include/openmc/settings.h @@ -150,6 +150,7 @@ extern double source_rejection_fraction; //!< Minimum fraction of source sites extern int max_history_splits; //!< maximum number of particle splits for weight windows +extern int max_secondaries; //!< maximum number of secondaries in the bank extern int64_t ssw_max_particles; //!< maximum number of particles to be //!< banked on surfaces per process extern int64_t ssw_max_files; //!< maximum number of surface source files diff --git a/openmc/settings.py b/openmc/settings.py index ce3743ff5d1..04bb4fbc71f 100644 --- a/openmc/settings.py +++ b/openmc/settings.py @@ -128,6 +128,10 @@ class Settings: Maximum number of times a particle can split during a history .. versionadded:: 0.13 + max_secondaries : int + Maximum secondary bank size + + .. versionadded:: 0.15.3 max_tracks : int Maximum number of tracks written to a track file (per MPI process). @@ -1137,6 +1141,16 @@ def max_history_splits(self, value: int): cv.check_greater_than('max particle splits', value, 0) self._max_history_splits = value + @property + def max_secondaries(self) -> int: + return self._max_secondaries + + @max_secondaries.setter + def max_secondaries(self, value: int): + cv.check_type('maximum secondary bank size', value, Integral) + cv.check_greater_than('max secondary bank size', value, 0) + self._max_secondaries = value + @property def max_tracks(self) -> int: return self._max_tracks @@ -1673,6 +1687,11 @@ def _create_max_history_splits_subelement(self, root): elem = ET.SubElement(root, "max_history_splits") elem.text = str(self._max_history_splits) + def _create_max_secondaries_subelement(self, root): + if self._max_secondaries is not None: + elem = ET.SubElement(root, "max_secondaries") + elem.text = str(self._max_secondaries) + def _create_max_tracks_subelement(self, root): if self._max_tracks is not None: elem = ET.SubElement(root, "max_tracks") @@ -2073,6 +2092,11 @@ def _max_history_splits_from_xml_element(self, root): if text is not None: self.max_history_splits = int(text) + def _max_secondaries_from_xml_element(self, root): + text = get_text(root, 'max_secondaries') + if text is not None: + self.max_secondaries = int(text) + def _max_tracks_from_xml_element(self, root): text = get_text(root, 'max_tracks') if text is not None: diff --git a/src/finalize.cpp b/src/finalize.cpp index e38b0b251cb..25b471a8bd2 100644 --- a/src/finalize.cpp +++ b/src/finalize.cpp @@ -92,6 +92,7 @@ int openmc_finalize() settings::max_lost_particles = 10; settings::max_order = 0; settings::max_particles_in_flight = 100000; + settings::max_secondaries = 10000; settings::max_particle_events = 1'000'000; settings::max_history_splits = 10'000'000; settings::max_tracks = 1000; diff --git a/src/physics.cpp b/src/physics.cpp index 3c06e543de1..509dce7c18f 100644 --- a/src/physics.cpp +++ b/src/physics.cpp @@ -115,7 +115,7 @@ void sample_neutron_reaction(Particle& p) // Make sure particle population doesn't grow out of control for // subcritical multiplication problems. - if (p.secondary_bank().size() >= 10000) { + if (p.secondary_bank().size() >= settings::max_secondaries) { fatal_error( "The secondary particle bank appears to be growing without " "bound. You are likely running a subcritical multiplication problem " @@ -210,13 +210,23 @@ void create_fission_sites(Particle& p, int i_nuclide, const Reaction& rx) site.particle = ParticleType::neutron; site.time = p.time(); site.wgt = 1. / weight; - site.parent_id = p.id(); - site.progeny_id = p.n_progeny()++; site.surf_id = 0; // Sample delayed group and angle/energy for fission reaction sample_fission_neutron(i_nuclide, rx, &site, p); + // Reject site if it exceeds time cutoff + if (site.delayed_group > 0) { + double t_cutoff = settings::time_cutoff[static_cast(site.particle)]; + if (site.time > t_cutoff) { + continue; + } + } + + // Set parent and progeny IDs + site.parent_id = p.id(); + site.progeny_id = p.n_progeny()++; + // Store fission site in bank if (use_fission_bank) { int64_t idx = simulation::fission_bank.thread_safe_append(site); @@ -1069,6 +1079,10 @@ void sample_fission_neutron( // set the delayed group for the particle born from fission site->delayed_group = group; + // Sample time of emission based on decay constant of precursor + double decay_rate = rx.products_[site->delayed_group].decay_rate_; + site->time -= std::log(prn(p.current_seed())) / decay_rate; + } else { // ==================================================================== // PROMPT NEUTRON SAMPLED diff --git a/src/physics_mg.cpp b/src/physics_mg.cpp index 5ebef9c1417..4c28cb1795a 100644 --- a/src/physics_mg.cpp +++ b/src/physics_mg.cpp @@ -139,8 +139,6 @@ void create_fission_sites(Particle& p) site.particle = ParticleType::neutron; site.time = p.time(); site.wgt = 1. / weight; - site.parent_id = p.id(); - site.progeny_id = p.n_progeny()++; // Sample the cosine of the angle, assuming fission neutrons are emitted // isotropically @@ -165,6 +163,24 @@ void create_fission_sites(Particle& p) // of the code, 0 is prompt. site.delayed_group = dg + 1; + // If delayed product production, sample time of emission + if (dg != -1) { + auto& macro_xs = data::mg.macro_xs_[p.material()]; + double decay_rate = + macro_xs.get_xs(MgxsType::DECAY_RATE, 0, nullptr, nullptr, &dg, 0, 0); + site.time -= std::log(prn(p.current_seed())) / decay_rate; + + // Reject site if it exceeds time cutoff + double t_cutoff = settings::time_cutoff[static_cast(site.particle)]; + if (site.time > t_cutoff) { + continue; + } + } + + // Set parent and progeny ID + site.parent_id = p.id(); + site.progeny_id = p.n_progeny()++; + // Store fission site in bank if (use_fission_bank) { int64_t idx = simulation::fission_bank.thread_safe_append(site); diff --git a/src/settings.cpp b/src/settings.cpp index afa42a3c5e6..03d42bb9da1 100644 --- a/src/settings.cpp +++ b/src/settings.cpp @@ -114,6 +114,7 @@ int max_order {0}; int n_log_bins {8000}; int n_batches; int n_max_batches; +int max_secondaries {10000}; int max_history_splits {10'000'000}; int max_tracks {1000}; ResScatMethod res_scat_method {ResScatMethod::rvs}; @@ -1144,6 +1145,11 @@ void read_settings_xml(pugi::xml_node root) weight_windows_on = get_node_value_bool(root, "weight_windows_on"); } + if (check_for_node(root, "max_secondaries")) { + settings::max_secondaries = + std::stoi(get_node_value(root, "max_secondaries")); + } + if (check_for_node(root, "max_history_splits")) { settings::max_history_splits = std::stoi(get_node_value(root, "max_history_splits")); diff --git a/src/tallies/tally_scoring.cpp b/src/tallies/tally_scoring.cpp index e73fb90f311..e88fd36c4cb 100644 --- a/src/tallies/tally_scoring.cpp +++ b/src/tallies/tally_scoring.cpp @@ -1624,8 +1624,7 @@ void score_general_mg(Particle& p, int i_tally, int start_index, tally.estimator_ == TallyEstimator::COLLISION) { if (settings::survival_biasing) { // Determine weight that was absorbed - wgt_absorb = p.wgt_last() * p.neutron_xs(p.event_nuclide()).absorption / - p.neutron_xs(p.event_nuclide()).total; + wgt_absorb = p.wgt_last() * p.macro_xs().absorption / p.macro_xs().total; // Then we either are alive and had a scatter (and so g changed), // or are dead and g did not change diff --git a/tests/unit_tests/test_settings.py b/tests/unit_tests/test_settings.py index 7f202bcdc73..6611e4227e0 100644 --- a/tests/unit_tests/test_settings.py +++ b/tests/unit_tests/test_settings.py @@ -67,6 +67,7 @@ def test_export_to_xml(run_in_tmpdir): ) } s.max_particle_events = 100 + s.max_secondaries = 1_000_000 s.source_rejection_fraction = 0.01 # Make sure exporting XML works @@ -144,4 +145,5 @@ def test_export_to_xml(run_in_tmpdir): assert s.random_ray['distance_active'] == 100.0 assert s.random_ray['ray_source'].space.lower_left == [-1., -1., -1.] assert s.random_ray['ray_source'].space.upper_right == [1., 1., 1.] + assert s.max_secondaries == 1_000_000 assert s.source_rejection_fraction == 0.01