Added test of volume calc from MG mode, then corrected 2 issues: the first led to #1698, the second led to the test failing as volume calcs need atom densities but they existed in a different location in MG mode. To fix the former, if blocks were placed to point to the MG nuclide data as necessary, and the latter by calling Material.finalize() at the appropriate spot in the MG code

src/material.cpp

@@ -349,24 +349,26 @@ Material::~Material()
 void Material::finalize()
 {
   // Set fissionable if any nuclide is fissionable
-  for (const auto& i_nuc : nuclide_) {
-    if (data::nuclides[i_nuc]->fissionable_) {
-      fissionable_ = true;
-      break;
+  if (settings::run_CE) {
+    for (const auto& i_nuc : nuclide_) {
+      if (data::nuclides[i_nuc]->fissionable_) {
+        fissionable_ = true;
+        break;
+      }
     }
+
+    // Generate material bremsstrahlung data for electrons and positrons
+    if (settings::photon_transport &&
+        settings::electron_treatment == ElectronTreatment::TTB) {
+      this->init_bremsstrahlung();
+    }
+
+    // Assign thermal scattering tables
+    this->init_thermal();
   }
 
-  // Generate material bremsstrahlung data for electrons and positrons
-  if (settings::photon_transport &&
-      settings::electron_treatment == ElectronTreatment::TTB) {
-    this->init_bremsstrahlung();
-  }
-
-  // Assign thermal scattering tables
-  this->init_thermal();
-
-  // Normalize density
-  this->normalize_density();
+// Normalize density
+this->normalize_density();
 }
 
 void Material::normalize_density()

src/mgxs_interface.cpp

@@ -123,10 +123,14 @@ void MgxsInterface::create_macro_xs()
   // Therefore type(nuclides[mat->nuclide_[0]]) dictates type(macroxs).
   // At the same time, we will find the scattering type, as that will dictate
   // how we allocate the scatter object within macroxs.
+
   for (int i = 0; i < model::materials.size(); ++i) {
+    // First we have to normalize the densities as it has not been called yet
+    // for MG mode
+    auto& mat {model::materials[i]};
+    mat->finalize();
     if (kTs[i].size() > 0) {
       // Convert atom_densities to a vector
-      auto& mat {model::materials[i]};
       vector<double> atom_densities(
         mat->atom_density_.begin(), mat->atom_density_.end());
 

src/volume_calc.cpp

@@ -8,6 +8,7 @@
 #include "openmc/hdf5_interface.h"
 #include "openmc/material.h"
 #include "openmc/message_passing.h"
+#include "openmc/mgxs_interface.h"
 #include "openmc/nuclide.h"
 #include "openmc/output.h"
 #include "openmc/random_lcg.h"
@@ -237,7 +238,8 @@ vector<VolumeCalculation::Result> VolumeCalculation::execute() const
       // Create 2D array to store atoms/uncertainty for each nuclide. Later this
       // is compressed into vectors storing only those nuclides that are
       // non-zero
-      auto n_nuc = data::nuclides.size();
+      auto n_nuc = settings::run_CE ? data::nuclides.size()
+                                    : data::mg.nuclides_.size();
       xt::xtensor<double, 2> atoms({n_nuc, 2}, 0.0);
 
 #ifdef OPENMC_MPI
@@ -442,7 +444,8 @@ void VolumeCalculation::to_hdf5(
 
     vector<std::string> nucnames;
     for (int i_nuc : result.nuclides) {
-      nucnames.push_back(data::nuclides[i_nuc]->name_);
+      nucnames.push_back(settings::run_CE ? data::nuclides[i_nuc]->name_
+                                          : data::mg.nuclides_[i_nuc].name);
     }
 
     // Create array of total # of atoms with uncertainty for each nuclide

tests/regression_tests/volume_calc/test.py

@@ -100,6 +100,8 @@ class VolumeTest(PyAPITestHarness):
             for iso in ['H1', 'O16', 'B10', 'Mo99', 'U235']:
                 mat = openmc.XSdata(iso, groups)
                 mat.order = 0
+                mat.atomic_weight_ratio = \
+                    openmc.data.atomic_mass(iso) / openmc.data.NEUTRON_MASS
                 mat.set_scatter_matrix(scatter)
                 if iso == 'U235':
                     mat.set_nu_fission(np.multiply(nu, fiss))