Two very short videos showing you how the runes recharge, are embedded below.
You can see the lockouts. Runic Empowerment would help give you some randomly recharged runes if you get a rune strike and it procs the RE random chance. Beta 12604. Note in the video, at the beginning, I should say ‘outbreak’ but say something else.
I’m not so comfortable with how it plays out for tanking. I regularly have rune blackouts, where I need to do an attack (usually an AOE situation) and simply have nothing I can do (other than blood tap or ERW).
Next, here’s a video showing the 10s gap between rune recharges and how blood tap works. Basic stuff, but might be helpful to get your head around it.
Here or this forum post.