The big risk is tritium leakage.

To show the scale of the problem: if the world were powered by Helion's reactors (for all primary energy), and the tritium produced were just released into the environment and mixed completely with all water on the planet (including oceans, lakes, rivers, ground water, and ice), then it would lift all that water above the US regulatory limit for tritium in drinking water. All the water, including everything in every ocean.