From “Synthesis Problems”: The goal of the synthesis program is to create a reactor with deuterium and tritium, hydrogen isotopes containing one and two additional neutrons. This choice of fuel facilitates the problem of achieving a reaction that produces energy, but also has features that complicate the conversion of this energy source into a useful power plant. The most serious difficulty concerns the high-energy neutrons emitted in the deuterium-tritium reaction. These particles damage the reactor structure and make it radioactive. The chain of side effects ensures that any reactor that uses DT synthesis will be a large, expensive and unreliable source of energy.
As these shortcomings become more widely understood, frustration in the synthesis program will weaken the prospects of other synthesis programs, no matter how wisely redirected, to the coming decades.