Nuclear energy is released by every fissioning nucleus, about 200 Mev per fission. But as the fission fragments are slowed down and absorbed in the mass of the fuel rods, the nuclear energy is...
thermal energy is heat energy, temperature is a measurement of heatDifferent objects may contain the same heat only at different temperatures. Temperature is more like electric potential in the sense...
Energy=thermal capacity x temperature (assuming thermal capacity is independent of temperature). Just like Electric charge on a capacitor = capacitance x voltage.