Systems and methods for controlling a clearance between a rotor and a stator of a steam turbine during transient operations rely upon heating or cooling a shell support structure of the steam turbine that supports the stator of the steam turbine. Selectively heating or cooling the shell support structure makes it possible for thermal growth/contraction rates and magnitudes of the shell support structure to better match the thermal growth/contraction rates and magnitudes of a bearing support structure of the steam turbine during transient operations. As a result, the clearance between the rotor and the stator of the steam turbine can be maintained.