OpenMC TRISO example is lagging when the height is increased.

[Sharif Abu Darda]

I am trying to run the TRISO example in https://docs.openmc.org/en/latest/examples/triso.html

I am creating a surrounding water for the box and I increased the height of the box as 200 cm. Now, It takes 35 mins just to generate the xml files with a pf=0.35. Now, When I tried to run the K-effective it is stuck in 

.........................

Initializing source particles...

 ====================>     K EIGENVALUE SIMULATION     <====================

  Bat./Gen.      k            Average k

  =========   ========   ====================

and not goes to first batch even after 30 mins. Below is the code I am using. What am I doing wrong. I first encounter the issue when I tried to generate a TRISO containing cylinder like fuel rods. That code was hanging, I tried the example code as it is, and just increased the height and the pf. But, the issue is still there. Does is possible to design a TRISO fuel rod in OpenMC? how? 

import openmc

from math import pi

from IPython.display import Image

import numpy as np

import matplotlib.pyplot as plt

import openmc.model 

# OpenMC simulation parameters

batches = 120                                                              

inactive = 20

particles = 10000

###############################################################################

#                 Exporting to OpenMC material.xml file

###############################################################################

# Material

water = openmc.Material()

water.set_density('g/cm3', 0.6928)

water.add_nuclide('H1', 0.11190, 'wo')

water.add_nuclide('O16', 0.88810, 'wo')

water.add_nuclide('B10', 1.4e-4, 'wo')

fuel = openmc.Material()

fuel.set_density('g/cm3', 10.5)

fuel.add_nuclide('U235', 4.6716e-02)

fuel.add_nuclide('U238', 2.8697e-01)

fuel.add_nuclide('O16',  5.0000e-01)

fuel.add_element('C', 1.6667e-01)

buff = openmc.Material()

buff.set_density('g/cm3', 1.0)

buff.add_element('C', 1.0)

buff.add_s_alpha_beta('c_Graphite')

PyC1 = openmc.Material()

PyC1.set_density('g/cm3', 1.9)

PyC1.add_element('C', 1.0)

PyC1.add_s_alpha_beta('c_Graphite')

PyC2 = openmc.Material()

PyC2.set_density('g/cm3', 1.87)

PyC2.add_element('C', 1.0)

PyC2.add_s_alpha_beta('c_Graphite')

SiC = openmc.Material()

SiC.set_density('g/cm3', 3.2)

SiC.add_element('C', 0.5)

SiC.add_element('Si', 0.5)

graphite = openmc.Material()

graphite.set_density('g/cm3', 1.1995)

graphite.add_element('C', 1.0)

graphite.add_s_alpha_beta('c_Graphite')

# Instantiate a Materials collection and export to XML

materials_file = openmc.Materials([water, fuel, buff, PyC1, PyC2, SiC, graphite])

materials_file.export_to_xml()

###############################################################################

#                 Exporting to OpenMC geometry.xml file

###############################################################################

########################################################## Instantiate Surfaces 

X_0 = openmc.XPlane(x0=0, name='X_0')

Y_0 = openmc.YPlane(y0=0, name='Y_0')

Z_0 = openmc.ZPlane(z0=0, name='Z_0')

min_x = openmc.XPlane(x0=-0.5)

max_x = openmc.XPlane(x0=0.5)

min_y = openmc.YPlane(y0=-0.5)

max_y = openmc.YPlane(y0=0.5)

min_z = openmc.ZPlane(z0=-108.3, boundary_type='reflective')

max_z = openmc.ZPlane(z0=91.7, boundary_type='reflective')

fuel_B_water = openmc.ZCylinder(x0=0, y0=0, r=3.0, boundary_type= 'reflective')

########################################################### Instantiate Cells 

spheres = [openmc.Sphere(r=1e-3*r)

           for r in [45.0, 51.0, 54.5, 58.0]]

cells = [openmc.Cell(fill=fuel, region=-spheres[0]),

         openmc.Cell(fill=buff, region=+spheres[0] & -spheres[1]),

         openmc.Cell(fill=PyC1, region=+spheres[1] & -spheres[2]),

         openmc.Cell(fill=SiC, region=+spheres[2] & -spheres[3]),

         openmc.Cell(fill=PyC2, region=+spheres[3])]

triso_univ = openmc.Universe(cells=cells)

region = +min_x & -max_x & +min_y & -max_y & +min_z & -max_z

outer_radius = 61.5*1e-3

centers = openmc.model.pack_spheres(radius=outer_radius, region=region, pf=0.35)

trisos = [openmc.model.TRISO(outer_radius, triso_univ, c) for c in centers]

box = openmc.Cell(region=region)

lower_left, upper_right = box.region.bounding_box

shape = (1, 1, 1)

pitch = (upper_right - lower_left)/shape

lattice = openmc.model.create_triso_lattice(trisos, lower_left, pitch, shape, graphite)

box.fill = lattice

Bundle_B_water = openmc.Cell(region= -fuel_B_water & +X_0 & +max_x & +min_z & -max_z | -fuel_B_water &-X_0 & -min_x & +min_z & -max_z | -fuel_B_water &-Y_0 & -min_y & +min_z & -max_z | -fuel_B_water &+Y_0  & +max_y & +min_z & -max_z, fill= water)

########################################################### Instantiate Universes 

root = openmc.Universe(universe_id=0)

root.add_cells([box, Bundle_B_water])

geometry = openmc.Geometry(root)

geometry.export_to_xml()

###############################################################################

#                   Exporting to OpenMC settings.xml file

###############################################################################

# Instantiate a Settings object, set all runtime parameters, and export to XML

settings_file = openmc.Settings()

settings_file.batches = batches

settings_file.inactive = inactive

settings_file.particles = particles

bounds = [-0.5,-0.5,-108.3,0.5,0.5,91.7]

uniform_dist = openmc.stats.Box(bounds[:3], bounds[3:] )#only_fissionable=True)

settings_file.source = openmc.source.Source(space=uniform_dist)

settings_file.export_to_xml()

###############################################################################

#                   Exporting to OpenMC plot.xml file

###############################################################################

plot_6 = openmc.Plot()

plot_6.basis ='xy'

plot_6.origin = [0, 0, 0]

plot_6.width = [4, 4]

plot_6.pixels = [500, 500]

plot_6.color_by = 'material'

plot = openmc.Plot()

plot.basis ='xz'

plot.origin = [0, 0, 0]

plot.width = [50, 450]

plot.pixels = [500, 500]

plot.color_by = 'material'

plots = openmc.Plots()

plots += [plot_6, plot]

plots.export_to_xml()

My fuel rod containing TRISO is below. Here instead of a box region, I used a cylinder region and keep everything else to generate TRISO as same as example. 

fuel_top= openmc.ZPlane(z0= +91.7)

bottom_cap_in= openmc.ZPlane(z0= -108.3)

fuel_B_fuel = openmc.ZCylinder(x0=0, y0=0, r=0.3922)

region_1= -fuel_B_fuel & +bottom_cap_in & -fuel_top

Bundle_B_fuel_1 = openmc.Cell(name='cell 4', region=region_1)

outer_radius_1 = 61.5*1e-3

centers_1 = openmc.model.pack_spheres(radius=outer_radius_1, region=region_1, pf=0.35)

trisos_1 = [openmc.model.TRISO(outer_radius_1, triso_univ_1, c) for c in centers_1]

ll, ur = Bundle_B_fuel_1.region.bounding_box

shape_1 = (1, 1, 1)

pitch_1 = (ur - ll)/shape_1

lattice1 = openmc.model.create_triso_lattice(trisos_1, ll, pitch_1, shape_1, graphite)

Bundle_B_fuel_1.fill = lattice1

Please guide. 

[pshr...@gmail.com]

Hi Sharif,

One thing that jumps out to me is the shape of the TRISO lattice. I'd try creating a TRISO lattice with a shape greater than (1, 1, 1). The lattice is used to accelerate the cell containment search when sourcing and tracking particles by limiting the search to TRISOs in the same lattice cell as the particle. With a shape of (1, 1, 1), all of the TRISOs are in the same lattice cell and in turn all of the TRISOs are in the search list, which is likely why it's taking so long to source those particles.

As a starting point, I've used a shape that is something like the size of the TRISO region divided by 2 diameters of the TRISO particle in each dimension - meaning you'll have ~8-10 TRISOs per lattice cell to search. For your model with a box width of 1 cm and an outer TRISO radius of 0.0613 cm this would result in a shape of (4, 4, 4). This is just a guideline though and something like (8, 8, 8) would be totally reasonable as well. The optimal shape for performance will vary model to model, so feel free to use your best judgement of course.

I hope this helps.

Best regards,

Patrick Shriwise
608-446-8173

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