The Nuclear is one of the more advanced grabs. Reach with your back hand across your body and grab the heel edge between the nose and your front binding. Because your back hand has to travel all the way past your front foot, the board has to come to you - this grab doesn't work by reaching down.
Learn it on heelside straight airs off the L-kicker, where you have enough airtime to set up the grab. Ride in with a progressive heelside edge and pop off the kicker. In the air, keep the handle close to your front hip with your arms bent - if your leading arm gets pulled straight, you'll never reach the grab. Push the handle down, let go with your back hand, then bend your front leg and straighten your back leg. This shifts the nose up toward your free hand. Letting the board turn slightly backside in the air (like a small shifty) brings the heel edge even closer to your back hand.
Here is a good explanation, but executed without a kicker:
Video by Julia Rick
Key tips
- Grab with your back hand on the heel edge, between the nose and your front binding
- Keep the handle close to your front hip with bent arms - this is what makes the reach possible
- Bend your front leg and straighten your back leg to bring the nose up to your hand
- A slight backside shifty in the air makes the grab much easier to reach
- Bring the board to your hand, not your hand to the board
- Build up to it: comfortable grabbed airs first, then shifties, then combine them into the Nuclear
See a map of all grabs here.