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Johann Andreas von Segner trained in medicine and later worked in mathematics, physics and astronomy. His institutional biography emphasizes fluid mechanics and his development of a reaction water wheel, an early hydraulic turbine.^[ref] The apparatus turns a redirected water flow into torque: the exiting fluid carries angular momentum, and its change is balanced by a reaction on the rotor. This makes the device an example of how a conservation law becomes a mechanical design principle.

Homepage: www.catalogus-professorum-halensis.de/segner-johann-andreas.html

A nuclear power plant converts energy from controlled nuclear fission into electrical energy. A nuclear reactor produces heat; a coolant carries it to the working cycle; a turbine drives an electrical generator. A pressurized water reactor transfers heat to a separate steam circuit, whereas a boiling water reactor generates steam in the reactor vessel.^[ref]

If thermal input is $P_{\mathrm{th}}$ and conversion efficiency is $\eta$, gross electrical output is approximately $\eta P_{\mathrm{th}}$; the remaining thermal power must be rejected. The plant also needs its own electrical supply, so gross output differs from net export. After the chain reaction stops, decay heat still requires removal.

A turbine extracts mechanical work from a flowing fluid through interaction with a rotating set of blades. Steam, hot gas or water changes its momentum while passing through the rotor, producing torque on the shaft. A steam turbine can drive an electrical generator in a thermal power station.

For steady axial through-flow in an ideal control-volume model, shaft torque is $\tau =\dot{m}(r_1{v}_{\theta 1}-r_2{v}_{\theta 2})$, the rate at which fluid angular momentum is removed. Here $v_{\theta }$ is the tangential velocity component and $r$ the radius. Shaft power is $P=\tau \Omega$ at angular speed $\Omega$. The relation connects blade-induced changes in flow direction with useful output; losses and operating conditions determine actual conversion efficiency.