From Wiki ...... Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy (in terms of mass in its rest frame) by radiation, such as an alpha particle, beta particle

Which was linked from en.wikipedia.org/wiki/Nuclear_fusion which also mentions the products like - alpha particles.

The problem, as described, with Tokamacs is the science of finding materials that can cope with the temperatures of the plasma and maybe alpha particles. Particularly the ITER being slated for success in 2035, when it is projected to produce 500Mw of excess energy for a few seconds. At an accumulated cost of 50 Billion (currency could be any given it is a guess!).

The NS article is not specific on the radioactive mechanisms, the article is a discussion of 2076 among other articles focusing on other areas of futurology.