Can a player have these kind of spells or are they limited to NPC´s? I remember that the corresponding mentor spirits and tradition are limited to NPC´s, but does this prevent me from using the spells too?

In theory, the only thing stopping a player from taking a Threat tradition is the fact that the GM should bop him on the nose and say "stop being a stupid."

Also in theory, there's no reason a player can't research and use the radiation spells and the like, and that should be easier (for a hermetic or something, anyway,) than the spirits and traditions, but again, bop him on the nose and tell him not to be a stupid. For one thing, the radiation rules are pain-in-the-ass annoying, for anything, a dude who goes around murdering people with magically-induced ionized radiation is going to get himself ganked fast.

I'm pretty sure Radiation sells are restricted to Toxic shamans, but honestly, whether I'd let a player take a Toxic tradition depends on the player. If they're the kind of person who can play a deep character with a complex psyche, then let them play a Toxic on the path to madness, then revoke their character when they truly reach the abyss. That sounds like an interesting story to me, and isn't that what RPGs are all about? That being said, if they're not the right kind of player, don't let them.

Ditto for Blood magic. If you only practice sacrifices on the evil, theoretically you can keep your morals; until it twists you on the inside, that is.