The Impossible Astronaut - S6-E2
Audio problem: When the Doctor sits in the Oval Office chair, Secret Service Agents aim their revolvers at him. As they do, the sound of a pistol slide racking is heard. None of them are doing anything except raising and aiming their revolvers at him.
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.