https://www.turbinegenerator.org/steam/types-steam-turbines/reaction/

http://www.mechanicalengineeringsite.com/impulse-turbine-reaction-turbine-principle-working-difference/

http://www.explainthatstuff.com/turbines.html

http://www.mechanicalbooster.com/2018/01/reaction-turbine.html

Hope this will help....thank you

A reaction turbine develops torque by reacting to the pressure or weight of a fluid and its operation is described by Newton's third law of motion (action and reaction are equal and opposite).In a reaction turbine, the nozzles that discharge the working fluid are attached to the rotor. The acceleration of the fluid leaving the nozzles produces a reaction force on the pipes, causing the rotor to move in the opposite direction to that of the fluid (so it takes reaction not action of fluid pressure). As flow goes through the nozzle and rotor rows, the flow’s static pressure is continually decreasing. Some of that drop in static pressure takes place in the nozzle row, and most takes place in the rotor row. It so happens that pressure decreases that happen in the rotor row are referred to as ‘reaction’ .

Of course the torque on the turbine wheel is the result of steam reaction on the blades. One may think black box, i.e. torque as difference of moment of momentum in versus moment of momentum out. Alternatively, one may think pressure distribution on the trubine blade. In common language, one speaks of "action" turbine stage versus "reaction turbine stage". In the action turbine stage all the fluid expansion occurs in the stator while, correspondingly, in the reaction turbine stage would occur in the rotor. Actually there is no pure action or reaction stage, both due to the radius distribution and to change in regime. It's better to use the term "degree of reaction". In my domain, gas turbines, the typical range is close to 0 for the high pressure stage and around 0.5 for the low pressure stage(s). It's very rare to have conditions with degree of reaction close to 1.0, i.e. "reaction turbine", except maybe during starting. Although the duality action/reaction is mostly a matter of language stretching, it's still simple and not misleading for the ones with minimal understanding in the domain.

Of course, it works by reducing the pressure but here one newton law works called newton third law which is based on reaction equal to action. for example, in impulse turbine , they work on newton second law which is the rate of change of momentum which is also known as impulse and for the same reason this turbine is called impulse turbine.

As a result of pressure drop in the moving blade, a reaction force will be produced. This force will make the blades to rotate.