Improve subchannel mesh generator validation

  Guard quad and tri assembly mesh generators against invalid axial grids,
  zero-length domains, and malformed spacer/blockage inputs before mesh
  construction. Keep quadrilateral assemblies consistent by rejecting only
  1x1 layouts while allowing valid 1xN and Nx1 subchannel meshes.

  Fix triangular assembly block-id fallback handling so the deprecated
  block_id parameter is still honored when subchannel_block_id is not set.
  Also add a quad mesh-object guard so pin index lookup on no-pin 1xN/Nx1
  meshes reports a clear error instead of evaluating unsigned underflow
  arithmetic.

  Add detailed quad coverage for the 1x1 rejection while preserving 1x2
  and Nx1 generation behavior. Refs idaholab#32847

Author: kyriv1980

modules/subchannel/src/mesh/QuadSubChannelMesh.C

@@ -97,6 +97,9 @@ QuadSubChannelMesh::channelIndex(const Point & pt) const
 unsigned int
 QuadSubChannelMesh::getPinIndexFromPoint(const Point & p) const
 {
+  if (_n_pins == 0)
+    mooseError(name(), ": Cannot compute a pin index because this mesh has no pins.");
+
   Real offset_x = (_nx - 2) * _pitch / 2.0;
   Real offset_y = (_ny - 2) * _pitch / 2.0;
   unsigned int i = (p(0) + offset_x) / _pitch;
@@ -107,6 +110,9 @@ QuadSubChannelMesh::getPinIndexFromPoint(const Point & p) const
 unsigned int
 QuadSubChannelMesh::pinIndex(const Point & p) const
 {
+  if (_n_pins == 0)
+    mooseError(name(), ": Cannot compute a pin index because this mesh has no pins.");
+
   Real offset_x = (_nx - 2) * _pitch / 2.0;
   Real offset_y = (_ny - 2) * _pitch / 2.0;
   unsigned int i = (p(0) + offset_x) / _pitch;

modules/subchannel/src/meshgenerators/SCMDetailedQuadAssemblyMeshGenerator.C

@@ -63,14 +63,31 @@ SCMDetailedQuadAssemblyMeshGenerator::SCMDetailedQuadAssemblyMeshGenerator(
     _n_cells(getParam<unsigned int>("n_cells")),
     _nx(getParam<unsigned int>("nx")),
     _ny(getParam<unsigned int>("ny")),
-    _n_channels(_nx * _ny),
+    _n_channels(0),
     _side_gap(isParamValid("side_gap") ? getParam<Real>("side_gap") : getParam<Real>("gap")),
     _num_radial_parts(getParam<unsigned int>("num_radial_parts")),
     _subchannel_block_id(getParam<unsigned int>("subchannel_block_id")),
     _pin_block_id(getParam<unsigned int>("pin_block_id")),
     _elem_id(0)
 {
   const Real L = _unheated_length_entry + _heated_length + _unheated_length_exit;
+
+  if (_n_cells == 0)
+    mooseError(name(), ": The number of axial cells must be greater than zero");
+
+  if (L <= 0.0)
+    mooseError(name(), ": Total bundle length must be greater than zero");
+
+  if (_nx == 0 || _ny == 0)
+    mooseError(name(), ": The number of subchannels must be greater than zero in each direction");
+
+  if (_nx < 2 && _ny < 2)
+    mooseError(name(),
+               ": The number of subchannels cannot be less than 2 in both directions. "
+               "Smallest assembly allowed is either 2X1 or 1X2.");
+
+  _n_channels = _nx * _ny;
+
   const Real dz = L / _n_cells;
   for (unsigned int i = 0; i < _n_cells + 1; i++)
     _z_grid.push_back(dz * i);

modules/subchannel/src/meshgenerators/SCMDetailedTriAssemblyMeshGenerator.C

@@ -55,7 +55,7 @@ SCMDetailedTriAssemblyMeshGenerator::SCMDetailedTriAssemblyMeshGenerator(
     _n_rings(getParam<unsigned int>("nrings")),
     _flat_to_flat(getParam<Real>("flat_to_flat")),
     _num_radial_parts(getParam<unsigned int>("num_radial_parts")),
-    _subchannel_block_id(isParamValid("subchannel_block_id")
+    _subchannel_block_id(parameters.isParamSetByUser("subchannel_block_id")
                              ? getParam<unsigned int>("subchannel_block_id")
                              : getParam<unsigned int>("block_id")),
     _pin_block_id(getParam<unsigned int>("pin_block_id")),
@@ -65,12 +65,19 @@ SCMDetailedTriAssemblyMeshGenerator::SCMDetailedTriAssemblyMeshGenerator(
     _verbose(getParam<bool>("verbose_flag")),
     _elem_id(0)
 {
+  const Real L = _unheated_length_entry + _heated_length + _unheated_length_exit;
+
   if (_n_rings < 2)
     mooseError(name(),
                ": 'nrings' must be at least 2. In this mesh generator, the center pin counts as "
                "the first ring, so a 7-pin bundle uses nrings = 2.");
 
-  Real L = _unheated_length_entry + _heated_length + _unheated_length_exit;
+  if (_n_cells == 0)
+    mooseError(name(), ": The number of axial cells must be greater than zero");
+
+  if (L <= 0.0)
+    mooseError(name(), ": Total bundle length must be greater than zero");
+
   Real dz = L / _n_cells;
   for (unsigned int i = 0; i < _n_cells + 1; i++)
     _z_grid.push_back(dz * i);

modules/subchannel/src/meshgenerators/SCMQuadAssemblyMeshGenerator.C

@@ -83,24 +83,46 @@ SCMQuadAssemblyMeshGenerator::SCMQuadAssemblyMeshGenerator(const InputParameters
     _n_cells(getParam<unsigned int>("n_cells")),
     _nx(getParam<unsigned int>("nx")),
     _ny(getParam<unsigned int>("ny")),
-    _n_channels(_nx * _ny),
-    _n_gaps((_nx - 1) * _ny + (_ny - 1) * _nx),
-    _n_pins((_nx - 1) * (_ny - 1)),
+    _n_channels(0),
+    _n_gaps(0),
+    _n_pins(0),
     _side_gap(getParam<Real>("side_gap")),
     _subchannel_block_id(getParam<unsigned int>("subchannel_block_id")),
     _pin_block_id(getParam<unsigned int>("pin_block_id"))
 {
-  if (_spacer_z.size() != _spacer_k.size())
-    mooseError(name(), ": Size of vector spacer_z should equal size of spacer_k");
+  const Real total_length = _unheated_length_entry + _heated_length + _unheated_length_exit;
 
-  if (_z_blockage.size() != 2)
-    mooseError(name(), ": Size of vector z_blockage must be 2");
+  if (_n_cells == 0)
+    mooseError(name(), ": The number of axial cells must be greater than zero");
+
+  if (total_length <= 0.0)
+    mooseError(name(), ": Total bundle length must be greater than zero");
+
+  if (_nx == 0 || _ny == 0)
+    mooseError(name(), ": The number of subchannels must be greater than zero in each direction");
 
   if (_nx < 2 && _ny < 2)
     mooseError(name(),
                ": The number of subchannels cannot be less than 2 in both directions. "
                "Smallest assembly allowed is either 2X1 or 1X2.");
 
+  _n_channels = _nx * _ny;
+  _n_gaps = (_nx - 1) * _ny + (_ny - 1) * _nx;
+  _n_pins = (_nx - 1) * (_ny - 1);
+
+  if (_spacer_z.size() != _spacer_k.size())
+    mooseError(name(), ": Size of vector spacer_z should equal size of spacer_k");
+
+  for (const auto spacer_z : _spacer_z)
+    if (spacer_z < 0.0 || spacer_z > total_length)
+      mooseError(name(), ": Spacer locations must be between zero and total bundle length");
+
+  if (_z_blockage.size() != 2)
+    mooseError(name(), ": Size of vector z_blockage must be 2");
+
+  if (_z_blockage.front() > _z_blockage.back())
+    mooseError(name(), ": z_blockage inlet location must not exceed outlet location");
+
   if (!_index_blockage.empty() &&
       *std::max_element(_index_blockage.begin(), _index_blockage.end()) > (_n_channels - 1))
     mooseError(name(), ": Blocked subchannel index exceeds valid subchannel range");
@@ -122,10 +144,6 @@ SCMQuadAssemblyMeshGenerator::SCMQuadAssemblyMeshGenerator(const InputParameters
   SubChannelMesh::generateZGrid(
       _unheated_length_entry, _heated_length, _unheated_length_exit, _n_cells, _z_grid);
 
-  if (_spacer_z.size() &&
-      _spacer_z.back() > _unheated_length_entry + _heated_length + _unheated_length_exit)
-    mooseError(name(), ": Location of spacers must be less than total bundle length");
-
   initializeChannelData();
 }
 

modules/subchannel/src/meshgenerators/SCMTriAssemblyMeshGenerator.C

@@ -63,7 +63,7 @@ SCMTriAssemblyMeshGenerator::SCMTriAssemblyMeshGenerator(const InputParameters &
     _unheated_length_entry(getParam<Real>("unheated_length_entry")),
     _heated_length(getParam<Real>("heated_length")),
     _unheated_length_exit(getParam<Real>("unheated_length_exit")),
-    _subchannel_block_id(isParamValid("subchannel_block_id")
+    _subchannel_block_id(params.isParamSetByUser("subchannel_block_id")
                              ? getParam<unsigned int>("subchannel_block_id")
                              : getParam<unsigned int>("block_id")),
     _pin_block_id(getParam<unsigned int>("pin_block_id")),
@@ -88,21 +88,32 @@ SCMTriAssemblyMeshGenerator::SCMTriAssemblyMeshGenerator(const InputParameters &
     _n_gaps(0),
     _elem_id(0)
 {
+  const Real total_length = _unheated_length_entry + _heated_length + _unheated_length_exit;
+
   if (_n_rings < 2)
     mooseError(name(),
                ": 'nrings' must be at least 2. In this mesh generator, the center pin counts as "
                "the first ring, so a 7-pin bundle uses nrings = 2.");
 
+  if (_n_cells == 0)
+    mooseError(name(), ": The number of axial cells must be greater than zero");
+
+  if (total_length <= 0.0)
+    mooseError(name(), ": Total bundle length must be greater than zero");
+
   if (_spacer_z.size() != _spacer_k.size())
     mooseError(name(), ": Size of vector spacer_z should be equal to size of vector spacer_k");
 
-  if (_spacer_z.size() &&
-      _spacer_z.back() > _unheated_length_entry + _heated_length + _unheated_length_exit)
-    mooseError(name(), ": Location of spacers should be less than the total bundle length");
+  for (const auto spacer_z : _spacer_z)
+    if (spacer_z < 0.0 || spacer_z > total_length)
+      mooseError(name(), ": Location of spacers should be between zero and total bundle length");
 
   if (_z_blockage.size() != 2)
     mooseError(name(), ": Size of vector z_blockage must be 2");
 
+  if (_z_blockage.front() > _z_blockage.back())
+    mooseError(name(), ": z_blockage inlet location must not exceed outlet location");
+
   if (*max_element(_reduction_blockage.begin(), _reduction_blockage.end()) > 1)
     mooseError(name(), ": The area reduction of the blocked subchannels cannot be more than 1");
 
@@ -117,7 +128,7 @@ SCMTriAssemblyMeshGenerator::SCMTriAssemblyMeshGenerator(const InputParameters &
       _unheated_length_entry, _heated_length, _unheated_length_exit, _n_cells, _z_grid);
 
   // Defining the total length from 3 axial sections
-  Real L = _unheated_length_entry + _heated_length + _unheated_length_exit;
+  Real L = total_length;
 
   // Defining the position of the spacer grid in the numerical solution array
   std::vector<int> spacer_cell;

modules/subchannel/test/tests/mesh/detailed_quad_assembly/tests

@@ -9,6 +9,13 @@
     recover = false
     requirement = 'The system will create a detailed mesh of the subchannels and fuel pins for quadrilateral assemblies (3x3)'
   []
+  [subchannel_number]
+    type = 'RunException'
+    input = 'coords.i'
+    cli_args = 'Mesh/assembly/nx=1 Mesh/assembly/ny=1'
+    expect_err = "The number of subchannels cannot be less than 2 in both directions\. Smallest assembly allowed is either 2X1 or 1X2\."
+    requirement = 'The system shall check the minimum number of subchannels for detailed quadrilateral assemblies'
+  []
 
   [1x2]
     type = Exodiff