Fusion reactor is theoretically possible...the challenge is to hold a core with a temperature equal to that of the sun in check. Science believes that it can be done with high tech magnets, used to hold the pile stable, and where a thermatic barrier would be introduced to keep it cool. The snag is, how to tap this heat for energy generation. In a current nuke plant, a heat generator is used between the primary and secondary loops meet--the highly radio-active primary loop of super heated steam gives off only heat to the secondary loop, which goes on to power turbines and generate electricity before going on to cooling towers to be condensed back into water. The problem presented with fusion reactors, in a nutshell, is how to get a secondary loop into the magnetized field without breaking the barrier.
I agree the fusion reactor is theoretically possible--the sun does it every day. The problem has always been one of engineering, not theory. That problem has not gone away, and is still a long way from being worked through to functioning, sustained, useable fusion reactors. It's easy to theoretically describe the necessary magnetic fields. Generating them, just the right shape, is the problem.