Abstract: The embodiments relate to a steam turbine with modular inserts that are removably insertable into an inner case. The modular inserts include a seal carrier modular insert located towards a first end of the steam turbine, for carrier seals located between the inner casing the rotor, that is cylindrically shaped and removably insertable into the inner casing, an inlet spiral insert, adjacent the seal carrier modular insert and removably insertable into the inner casing, for introducing steam into the steam expansion flow path so as to circumferentially distribute steam feed into the steam turbine; and a blade carrier modular insert, adjacent the inlet spiral insert, that is also cylindrically shaped and removably insertable into the inner casing, for retaining stationary blades.