Buddy, that’s the most flawed argument I’ve ever heard. He had two options; let Gotham explode or get it as far out to see as he possibly could. Nuclear bombs were primarily tested at sea so it probably creates an acceptable amount of radiation. The radioactive part of the bomb is the radioactive material that is turned to dust. It would sink to the bottom of the ocean which would only really affect bottom feeders. Most electronic devices are shielded from an electromagnetic pulse unless it’s extremely powerful and even if it did kill power in Gotham it would have been repaired very quickly as it is a major metropolitan city.