When do you think a nuclear fusion reactor will be perfected or at least become usable to replace a nuclear fission

Question: When do you think a nuclear fusion reactor will be perfected or at least become usable to replace a nuclear fission reactor?
- Keywords:
  fission,
  fusion
Asked by Cameron to Adrian, Gaia, Jim, Scott, Vicky on 7 Mar 2016.
- Adrian Buzatu answered on 7 Mar 2016:
  
  That is a great question! Scientists promised 50 years ago, and it still is not here. Maybe 50 years in the future … Science has been making progress though. It’s small steps in the right direction.
- Scott Lawrie answered on 8 Mar 2016:
  
  We have lots of experience in nuclear fusion – and with good reason! It’s going to give lots of energy for essentially free and with very few bad sides, unlike fission reactors. When we get it right, it will change the world.
  
  The problem is, though, that we’re essentially trying to harness the power or a star. That is not an easy thing to do and there are LOTS of steps along the way. For example, how do you operate a million-degree plasma just centimeters away from a magnet near absolute zero temperature?!
  
  A new (really crazy-cool shaped) fusion reactor called Wendelstein 7-X has just started up in Germany and another one is being built in France which will be even bigger and really help us understand how to make a real, usable, commercial reactor that could plug into the National Grid.

Question: When do you think a nuclear fusion reactor will be perfected or at least become usable to replace a nuclear fission reactor?