I have a quick question, I've checked the rules but I cannot find any satisfying answer to it.

Psychic Powers, can you use them in close combat? I see that they have a subtype of concentration, and I cannot find what that means?

Concentration merely means that (apart from reaction powers) you can only use them once per round, just like you can only use one action with the attack subtype (meaning you can't for example shoot someone with your boltpistol and then blast them with a psychic bolt).

Otherwise, yes, you can use psychic powers in melee.