DAGMC Cell Override Updates (#3888)

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>
Co-authored-by: Paul Romano <paul.k.romano@gmail.com>

Author: 3 people

docs/source/io_formats/geometry.rst

@@ -406,24 +406,55 @@ Each ``<dagmc_universe>`` element can have the following attributes or sub-eleme
 
     *Default*: None
 
-  :material_overrides:
-    This element contains information on material overrides to be applied to the
-    DAGMC universe. It has the following attributes and sub-elements:
-
-    :cell:
-      Material override information for a single cell. It contains the following
-      attributes and sub-elements:
-
-      :id:
-        The cell ID in the DAGMC geometry for which the material override will
-        apply.
-
-      :materials:
-        A list of material IDs that will apply to instances of the cell. If the
-        list contains only one ID, it will replace the original material
-        assignment of all instances of the DAGMC cell. If the list contains more
-        than one material, each material ID of the list will be assigned to the
-        various instances of the DAGMC cell.
+  :cell:
+    Zero or more ``<cell>`` sub-elements may appear to override properties of
+    individual DAGMC volumes. Each ``<cell>`` element supports the following
+    attributes and sub-elements:
+
+    :id:
+      The integer cell ID in the DAGMC geometry to override. Required.
+
+    :name:
+      An optional string label for the cell.
+
+      *Default*: None
+
+    :material:
+      The material ID to assign to this cell. Use ``void`` for vacuum. Multiple
+      space-separated IDs may be given to specify a distribmat (distributed
+      material) assignment. Required.
+
+    :temperature:
+      Temperature(s) in [K] to assign to the cell. Must be ≥ 0. Multiple
+      space-separated values may be given.
+
+      *Default*: None
+
+    :density:
+      Density in [g/cm³] to assign to the cell. Must be > 0. Requires a non-void
+      material fill. Multiple space-separated values may be given.
+
+      *Default*: None
+
+    :volume:
+      Volume of the cell in [cm³].
+
+      .. note:: DAGMC can compute cell volumes exactly from the triangulated
+                mesh surfaces. Specifying a manual volume risks inconsistency
+                with that capability.
+
+      *Default*: None
+
+    The following standard ``<cell>`` attributes are **not** supported inside
+    ``<dagmc_universe>`` and will raise an error if present: ``region``,
+    ``fill``, ``universe``, ``translation``, ``rotation``.
+
+    .. deprecated::
+      The ``<material_overrides>`` sub-element (containing ``<cell_override>``
+      children with ``<material_ids>``) is deprecated. A deprecation warning is
+      emitted and the overrides are converted to the ``<cell>`` format at parse
+      time. It is an error to specify both ``<material_overrides>`` and
+      ``<cell>`` sub-elements on the same ``<dagmc_universe>``.
 
     *Default*: None
 

include/openmc/cell.h

@@ -145,6 +145,30 @@ class Region {
   bool simple_; //!< Does the region contain only intersections?
 };
 
+//==============================================================================
+// XML parsing helpers for <cell> nodes
+//==============================================================================
+
+//! Parse material IDs from a <cell> XML node.
+//! \param node XML node containing a "material" attribute or child element
+//! \param cell_id Cell ID used in error messages
+//! \return Vector of material IDs (MATERIAL_VOID for "void")
+vector<int32_t> parse_cell_material_xml(pugi::xml_node node, int32_t cell_id);
+
+//! Parse temperatures in [K] from a <cell> XML node.
+//! Validates that all values are non-negative and the list is non-empty.
+//! \param node XML node containing a "temperature" attribute or child element
+//! \param cell_id Cell ID used in error messages
+//! \return Vector of temperatures in [K]
+vector<double> parse_cell_temperature_xml(pugi::xml_node node, int32_t cell_id);
+
+//! Parse densities in [g/cm³] from a <cell> XML node.
+//! Validates that all values are positive and the list is non-empty.
+//! \param node XML node containing a "density" attribute or child element
+//! \param cell_id Cell ID used in error messages
+//! \return Vector of densities in [g/cm³]
+vector<double> parse_cell_density_xml(pugi::xml_node node, int32_t cell_id);
+
 //==============================================================================
 
 class Cell {

include/openmc/dagmc.h

@@ -94,6 +94,10 @@ class DAGCell : public Cell {
 class DAGUniverse : public Universe {
 
 public:
+  using MaterialOverrides = std::unordered_map<int32_t, vector<int32_t>>;
+  using TemperatureOverrides = std::unordered_map<int32_t, vector<double>>;
+  using DensityOverrides = std::unordered_map<int32_t, vector<double>>;
+
   explicit DAGUniverse(pugi::xml_node node);
 
   //! Create a new DAGMC universe
@@ -112,6 +116,9 @@ class DAGUniverse : public Universe {
   //! Initialize the DAGMC accel. data structures, indices, material
   //! assignments, etc.
   void initialize();
+  void initialize(const MaterialOverrides& material_overrides,
+    const TemperatureOverrides& temperature_overrides,
+    const DensityOverrides& density_overrides = {});
 
   //! Reads UWUW materials and returns an ID map
   void read_uwuw_materials();
@@ -146,7 +153,8 @@ class DAGUniverse : public Universe {
 
   //! Assign a material overriding normal assignement to a cell
   //! \param[in] c The OpenMC cell to which the material is assigned
-  void override_assign_material(std::unique_ptr<DAGCell>& c) const;
+  void override_assign_material(std::unique_ptr<DAGCell>& c,
+    const MaterialOverrides& material_overrides) const;
 
   //! Return the index into the model cells vector for a given DAGMC volume
   //! handle in the universe
@@ -187,7 +195,9 @@ class DAGUniverse : public Universe {
   void set_id();        //!< Deduce the universe id from model::universes
   void init_dagmc();    //!< Create and initialise DAGMC pointer
   void init_metadata(); //!< Create and initialise dagmcMetaData pointer
-  void init_geometry(); //!< Create cells and surfaces from DAGMC entities
+  void init_geometry(const MaterialOverrides& material_overrides,
+    const TemperatureOverrides& temperature_overrides,
+    const DensityOverrides& density_overrides);
 
   std::string
     filename_; //!< Name of the DAGMC file used to create this universe
@@ -201,11 +211,6 @@ class DAGUniverse : public Universe {
                              //!< generate new material IDs for the universe
   bool has_graveyard_; //!< Indicates if the DAGMC geometry has a "graveyard"
                        //!< volume
-  std::unordered_map<int32_t, vector<int32_t>>
-    material_overrides_; //!< Map of material overrides
-                         //!< keys correspond to the DAGMCCell id
-                         //!< values are a list of material ids used
-                         //!< for the override
 };
 
 //==============================================================================