# Inconsistent Flux Results in Multi-group Mode **URL:** \ **Category:** User Support\ **Created:** [April 2, 2024, 12:25pm UTC](https://openmc.discourse.group/t/inconsistent-flux-results-in-multi-group-mode/4122 "2024-04-02T12:25:59Z")\ **Posts on this page:** 1\ **Page:** 1
**Author:** ![Visionary](https://avatars.discourse-cdn.com/v4/letter/v/13edae/32.png) [@Visionary](https://openmc.discourse.group/u/Visionary)\ **Post date:** [April 2, 2024, 12:25pm UTC](https://openmc.discourse.group/t/inconsistent-flux-results-in-multi-group-mode/4122/1 "2024-04-02T12:25:59Z")
When using multi-group mode in OpenMC, where I provided a set of cross sections and obtained flux distribution results. However, I encountered an unexpected inconsistency in the flux results when using two different enrichment levels of fuel. When simulating with a single fuel enrichment, the flux distribution appeared reasonable. However, when I simulated with two different enrichments, the flux results did not exhibit the expected variation between the two fuel types. This discrepancy is contrary to both fine modeling expectations and deterministic results. Could anyone provide insights or suggestions on what might be causing this issue? Thanks very much！ * * * ## Here are my codes import numpy as np import openmc %matplotlib inline from IPython.display import Image import numpy as np import matplotlib.pyplot as plt import openmc # Create a 2-group structure with arbitrary boundaries (the specific boundaries are unimportant) groups = openmc.mgxs.EnergyGroups([1e-5, 1e6, 20.0e6]) #lowEnrichmentAssembly\_xsdata lowEnrichmentAssembly\_xsdata = openmc.XSdata(‘lowEnrichmentAssembly’, groups) lowEnrichmentAssembly\_xsdata.order = 0 lowEnrichmentAssembly\_xsdata.set\_total([0.170114542, 0.377481276], temperature=294.) lowEnrichmentAssembly\_xsdata.set\_absorption([0.007605099,0.007113863], temperature=294.) lowEnrichmentAssembly\_xsdata.set\_fission([0.006416398, 0.002631272], temperature=294.) lowEnrichmentAssembly\_xsdata.set\_nu\_fission([0.016645917, 0.007355224], temperature=294.) lowEnrichmentAssembly\_xsdata.set\_chi([0.6981436,0.3018564], temperature=294.) scatter\_matrix1 = [[[0.117544123, 0.0451495759], [0.0, 0.370351157]]] scatter\_matrix1 = np.array(scatter\_matrix1) scatter\_matrix1 = np.rollaxis(scatter\_matrix1, 0, 3) lowEnrichmentAssembly\_xsdata.set\_scatter\_matrix(scatter\_matrix1, temperature=294.) #up\_xsdata upAssembly\_xsdata = openmc.XSdata(‘upAssembly’, groups) upAssembly\_xsdata.order = 0 upAssembly\_xsdata.set\_total([0.170259603, 0.370522199], temperature=294.) upAssembly\_xsdata.set\_absorption([0.008095127, 0.007957804], temperature=294.) upAssembly\_xsdata.set\_fission([0.006900317, 0.003546659], temperature=294.) upAssembly\_xsdata.set\_nu\_fission([0.019165554, 0.008389694], temperature=294.) upAssembly\_xsdata.set\_chi([0.6990006,0.3009994], temperature=294.) scatter\_matrix3 = [[[0.117426756,0.0449167458], [0.0, 0.363264991]]] scatter\_matrix3 = np.array(scatter\_matrix3) scatter\_matrix3 = np.rollaxis(scatter\_matrix3, 0, 3) upAssembly\_xsdata.set\_scatter\_matrix(scatter\_matrix3, temperature=294.) #down\_xsdata downAssembly\_xsdata = openmc.XSdata(‘downAssembly’, groups) downAssembly\_xsdata.order = 0 downAssembly\_xsdata.set\_total([0.170259603, 0.370522199], temperature=294.) downAssembly\_xsdata.set\_absorption([0.008095127, 0.007957804], temperature=294.) downAssembly\_xsdata.set\_fission([0.006900317, 0.003546659], temperature=294.) downAssembly\_xsdata.set\_nu\_fission([0.019165554, 0.008389694], temperature=294.) downAssembly\_xsdata.set\_chi([0.6990006,0.3009994], temperature=294.) scatter\_matrix4 = [[[0.117426756,0.0449167458], [0.0, 0.363264991]]] scatter\_matrix4 = np.array(scatter\_matrix4) scatter\_matrix4 = np.rollaxis(scatter\_matrix4, 0, 3) downAssembly\_xsdata.set\_scatter\_matrix(scatter\_matrix4, temperature=294.) #upAxialReflector\_xsdata upAxialReflectorAssembly\_xsdata = openmc.XSdata(‘upAxialReflectorAssembly’, groups) upAxialReflectorAssembly\_xsdata.order = 0 upAxialReflectorAssembly\_xsdata.set\_total([0.174079875, 0.424901412], temperature=294.) upAxialReflectorAssembly\_xsdata.set\_absorption([0.000711852, 0.001298070], temperature=294.) upAxialReflectorAssembly\_xsdata.set\_fission([0.0, 0.0], temperature=294.) upAxialReflectorAssembly\_xsdata.set\_nu\_fission([0.0, 0.0], temperature=294.) upAxialReflectorAssembly\_xsdata.set\_chi([0.0,0.0], temperature=294.) scatter\_matrix6 = [[[0.140148556, 0.0331868293], [0.0, 0.423591766]]] scatter\_matrix6 = np.array(scatter\_matrix6) scatter\_matrix6 = np.rollaxis(scatter\_matrix6, 0, 3) upAxialReflectorAssembly\_xsdata.set\_scatter\_matrix(scatter\_matrix6, temperature=294.) #downAxialReflector\_xsdata downAxialReflectorAssembly\_xsdata = openmc.XSdata(‘downAxialReflectorAssembly’, groups) downAxialReflectorAssembly\_xsdata.order = 0 downAxialReflectorAssembly\_xsdata.set\_total([0.174079875, 0.424901412], temperature=294.) downAxialReflectorAssembly\_xsdata.set\_absorption([0.000711852, 0.001298070], temperature=294.) downAxialReflectorAssembly\_xsdata.set\_fission([0.0, 0.0], temperature=294.) downAxialReflectorAssembly\_xsdata.set\_nu\_fission([0.0, 0.0], temperature=294.) downAxialReflectorAssembly\_xsdata.set\_chi([0.0,0.0], temperature=294.) scatter\_matrix7 = [[[0.140148556, 0.0331868293], [0.0, 0.423591766]]] scatter\_matrix7 = np.array(scatter\_matrix7) scatter\_matrix7 = np.rollaxis(scatter\_matrix7, 0, 3) downAxialReflectorAssembly\_xsdata.set\_scatter\_matrix(scatter\_matrix7, temperature=294.) mg\_cross\_sections\_file = openmc.MGXSLibrary(groups) mg\_cross\_sections\_file.add\_xsdata(lowEnrichmentAssembly\_xsdata) mg\_cross\_sections\_file.add\_xsdata(upAssembly\_xsdata) mg\_cross\_sections\_file.add\_xsdata(downAssembly\_xsdata) mg\_cross\_sections\_file.add\_xsdata(upAxialReflectorAssembly\_xsdata) mg\_cross\_sections\_file.add\_xsdata(downAxialReflectorAssembly\_xsdata) mg\_cross\_sections\_file.export\_to\_hdf5(‘mgxs.h5’) lowEnrichmentAssembly1 = openmc.Material() lowEnrichmentAssembly1.add\_macroscopic(‘lowEnrichmentAssembly’) upAssembly1 = openmc.Material() upAssembly1.add\_macroscopic(‘upAssembly’) downAssembly1 = openmc.Material() downAssembly1.add\_macroscopic(‘downAssembly’) upAxialReflectorAssembly1 = openmc.Material() upAxialReflectorAssembly1.add\_macroscopic(‘upAxialReflectorAssembly’) downAxialReflectorAssembly1 = openmc.Material() downAxialReflectorAssembly1.add\_macroscopic(‘downAxialReflectorAssembly’) materials\_file = openmc.Materials([downAxialReflectorAssembly1,upAxialReflectorAssembly1,downAssembly1,upAssembly1,lowEnrichmentAssembly1]) mg\_cross\_sections\_file.export\_to\_hdf5(‘mgxs.h5’) materials\_file.export\_to\_xml() #geometry top1 = openmc.ZPlane(z0=+52.5) top2 = openmc.ZPlane(z0=+52.5+25) top3 = openmc.ZPlane(z0=+52.5+25+20, boundary\_type=‘vacuum’) bottom1 = openmc.ZPlane(z0=-52.5) bottom2 = openmc.ZPlane(z0=-52.5-25) bottom3 = openmc.ZPlane(z0=-52.5-25-20, boundary\_type=‘vacuum’) assembly = openmc.model.hexagonal\_prism(edge\_length=17.15/1.732, orientation=‘x’, boundary\_type=‘reflective’) lowEnrichmentAssembly\_cell = openmc.Cell() lowEnrichmentAssembly\_cell.region = assembly & -top1 & +bottom1 lowEnrichmentAssembly\_cell.fill = lowEnrichmentAssembly1 upAssembly\_cell = openmc.Cell() upAssembly\_cell.region = assembly & -top2 & +top1 upAssembly\_cell.fill = upAssembly1 downAssembly\_cell = openmc.Cell() downAssembly\_cell.region = assembly & -bottom1 & +bottom2 downAssembly\_cell.fill = downAssembly1 upAxialReflectorAssembly\_cell = openmc.Cell() upAxialReflectorAssembly\_cell.region = assembly & -top3 & +top2 upAxialReflectorAssembly\_cell.fill = upAxialReflectorAssembly1 downAxialReflectorAssembly\_cell = openmc.Cell() downAxialReflectorAssembly\_cell.region = assembly & -bottom2 & +bottom3 downAxialReflectorAssembly\_cell.fill = downAxialReflectorAssembly1 u\_root = openmc.Universe() u\_root.add\_cells([lowEnrichmentAssembly\_cell,downAxialReflectorAssembly\_cell ,upAxialReflectorAssembly\_cell,downAssembly\_cell,upAssembly\_cell]) geom=openmc.Geometry(u\_root) geom.export\_to\_xml() # Instantiate an empty Tallies object tallies = openmc.Tallies() # Create mesh which will be used for tally mesh = openmc.RegularMesh() mesh.dimension = [1, 1, 196] mesh.lower\_left = [-17.15/1.732, -17.15/2,-97.5] mesh.upper\_right = [17.15/1.732, 17.15/2,97.5] # Create mesh filter for tally mesh\_filter = openmc.MeshFilter(mesh) tally = openmc.Tally(name=‘flux’) tally.filters = [mesh\_filter] tally.scores = [‘flux’] tallies.append(tally) tallies.export\_to\_xml() settings = openmc.Settings() settings.batches = 300 settings.inactive = 10 settings.particles = 10000 settings.energy\_mode = ‘multi-group’ settings.export\_to\_xml() openmc.run()