Question

how does a nuclear power plant and a thermal power plant work?each a para

Answer 1

A thermal power plant is a generic category of power plants that convert heat energy generated from a particular source into electrical energy. 

The basic principle involves heating water using either nuclear energy (as used in nuclear power plants) or  through fossil-fuel combustion (such as burning coal). The steam thus produced rotates a turbine which then drives an electrical generator in the thermal power plant, producing electricity.

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The nuclear power plant is thus merely a type of thermal power plant that uses nuclear fission as the source of heat (the nuclear energy here heats the water producing steam). It is this source of the heat energy (nuclear fission wherein splitting of nuclei releases energy) that differentiates it from other thermal power plants (such as those using coal burning to generate heat). 

Answer 2

Both work by production of heat energy which is used to heat water to produce steam and then this steam is used to run large turbines.
In thermal power heat is produced by the means of natural resources like coal, gas and other petroleum products in very large quantities. While in nuclear power uranium is mainly used to get energy for steam production. Uranium is broken by nuclear fission reaction which generates a lot of heat energy.