***called Super Critical steam or Universal Pressure.***
Would that be called a “Once Through” boiler with no reheat system? Lots of pressure and heat in them. Way more than than a regular “two stage” high press-reheat type boiler.
It could be called once through but it definitely has a Reheat Stage. Super Critical Boilers just jam the water in on one end and it comes out as steam on the other. Older types have steam separating headers that recycle hot water through the Boiler section. After this the steam is superheated and sent to the Turbine. This is all about funny properties called Enthalpy and Entropy and how energy can be ripped out of the heat imparted in the steam.
In a Supercitical unit, the water is actually pushed into the unit at 4500psi.. and by the time it gets to the Turbine simple hydraulic resistance decreases the pressure to 3600psi. The water never really flashes to steam, hence supercritical, and instead it just gets hotter. It goes through the water walls to contain the fireball of the furnace, then through the economizer to pick up heat from the last gases leaving the furnace, then through the primary superheater, then the secondary superheater then down to the Turbine.
Steam leaving the turbine is fed back up the the Reheater and then back down to the Turbine one more time and then into the Condenser where it is cooled to near room temperature by the cooling system which creates a vacuum. If you ever heated a gas can with water in the bottom and screwed the lid on, you can see what this does.. schlooop! The suction pulls that last steam across the biggest low pressure turbine blades before it gets cooled. This wrings that last tiny bit of energy out of the steam.