Trivia: At the beginning of the scene where Clara persuades Rigsy to give her his chronolock, a poster can be seen on a wall in the background, reading "DeLorean" (a Back to the Future reference) in Aurebesh (the writing system from Star Wars). (00:25:00)
Trivia: The amp that the Doctor is using when he's playing his electric guitar at the beginning is from Magpie Electricals, a recurring brand first introduced in Tenth Doctor episode "The Idiot's Lantern". And if you look closely, you'll see the clockwork squirrel mentioned in the previous episode sitting atop it.
Chosen answer: 1) When Stephen Moffat took over he ignored a lot of what had been developed before (there is not in-universe answer). 2) It would have killed Rose, so the Doctor absorbed the energy. His body regenerated before the energy could do a significant amount of damage that would prevent regeneration.