In a D-T reactor you're not losing energy from neutrons, you're using the neutrons to heat a coolant and turn a turbine. (And also to breed more tritium, but th

In a D-T reactor you're not losing energy from neutrons, you're using the neutrons to heat a coolant and turn a turbine. (And also to breed more tritium, but that still generates heat.) He3 is rare but deuterium is decidedly not. Fusion deuterium is about as easy as fusing He3, and the waste product of D-D is half He3, and half tritium which decays to He3 with a 12-year half-life. Fusion company Helion is building a hybrid D-D/D-He3, and says the combination would release only 5% of its energy as neutron radiation, compared to 80% from D-T. The neutrons would also have lower energy, below the activation energy of common reactor materials.