They will make the He-3 using D-D fusion reactors (which is not aneutronic) and waiting for collected tritium to decay into He-3 (12 years). In each shot, they have to remove the he3 and T to prevent them from reacting.
In the D-he3 reactors, they cannot fully prevent the side reactions of DD and DT. But they can minimize them by controlling the mixture of he3 and D in each shot and constantly extracting the T byproduct of D-he3. Basically, they will have high ratio of he3 to D ions so that all the D ions are likely to be used in D-he3 reactions. Removing and collecting the T in each shot removes the opportunity for D-T. It will probably work to an extent, but there will still be side reactions. The overall neutronicity will likely be in the 2-5 range in the D-He3 reactors.