We're not there yet, hence the goal of ITER to hopefully demonstrate the feasibility.
Achievements of TFTR - http://www.pppl.gov/projects/pages/t...ievements.html
TFTR did identify some instability issues, e.g. ballooning, but they also identified an enhanced reversed-shear mode during 1995, but TFTR was shutdown in 1997, so it's not clear that enhanced confinement methods are fully vetted.
- note Plasma Parameters for Shot 80539. While it achieved 10.7 MW of generated fusion power, the confinement time [itex]\tau[/itex] was 0.21 sec. One needs to achieve continuous operation on the order of 3.156 E7 sec, or a 90% CF to approach performance of current LWRs.
Hopefully ITER will demonstrate or perfect some of the processes developed with TFTR.
For reference - http://www.pppl.gov/projects/pages/tftr_docs.html