A rocket that uses nuclear power to heat a propellent usally liquid to a hight temperature for use as rocket fule.
A solid core nuclear rocket uses a solid reactor core to heat the propelent.
The nerva project buit and tested a nuclear rocket in the 1960s using Uranium 235 in the reactor and Hydrogen for the propellent.
The tested rocket had about 50,000 lbs thrust.
Other propelents were tested also. ISP or specific impulse is a measure of fule efficenct used for rockets. (Higher is better)
Propellent ............ ISP
H2 ............ 811
CH4 .......... 633
NH3 .......... 511
H2O .......... 405
CO2 .......... 331
N2 or CO ...265
Hydrogen and Oxygen in a chemical rocket for comparsion
H2+O2 ...... 453 vacume SSME (Space suttle Engines on back of the orbiter)