They’re using D-H3, which is aneutronic. There are also side-reactions which do produce neutrons, but perhaps it’s not enough to result in degradation.
Extracting tritium between pulses seems to be the key approach to reducing degradation. One of the company's patents [1] explains:
"The D-3He fusion reaction produces no neutrons as well (D+3He→4He (3.6 MeV)+H (14.7 MeV). However the D-D side reaction, while not as frequent, can generate 14.1 MeV neutrons through one of its fusion product reactions (D+T→4He+n+14.1 MeV). There is also the D-D reaction itself that produces a lower energy neutron (2.45 MeV) which is below the threshold for activation of most nuclear materials and is thus far less detrimental...Example systems and methods described herein may employ a 3He fuel cycle which may reduce or suppress a dangerous D-T side reaction by extracting the tritium ions as they are created. The extracted tritium is unstable and may beta decay in a relatively short period of 11 years to 3He, a primary fuel for the D-3He reaction. Accordingly, example systems, reactors and methods described herein may enjoy a self-sustaining fuel cycle where the required 3He to operate the reactor may be generated by the decay of tritium ions extracted from the reactor itself..."
The FAQ on the website [2] acknowledges their process "does create some 'activated materials' over the operating life of a power plant. Helion’s plants have been specifically designed to only use materials that would result in low activation, similar to what might be created by medical devices or other particle accelerators.
Our expectation is that a Helion plant could be fully decommissioned within a week without any lasting environmental impact."
