When Discrete ordinates method is selected, this node enables intensity conservation across internal boundaries. It is the default boundary condition for all interior boundaries. For P1 approximation and Rosseland approximation this boundary condition is not available since it is not needed.

More locations are available if the Radiation in participating media check box is selected under the Physical Model section. For example:
Heat Transfer in Solids>Radiation in Participating Media>Continuity on Interior Boundary

Physics Tab with Heat Transfer, Heat Transfer in Solids, Heat Transfer in Fluids, Heat Transfer in Porous Media, Heat Transfer in Building Materials, Bioheat Transfer, Heat Transfer with Surface-to-Surface Radiation, Heat Transfer with Radiation in Participating Media or Radiation in Participating Media selected:
Boundaries>Radiation in Participating Media>Continuity on Interior Boundary