Sure, those are problems if the Orion method is used inside the orbital region. However, if used after escaping from Earth's gravity well to accelerate towards

Sure, those are problems if the Orion method is used inside the orbital region. However, if used after escaping from Earth's gravity well to accelerate towards distant destinations, the only remaining issue is international law. Electromagnetic pulses decay as the inverse square law, radioactive fallout would be outside the Earth's gravity well and disperse harmlessly in space, the Van Allen belts are also not near enough to be affected. The only real risk would be from accidents while lifting that much fissile material to space, which could be mitigated by proper containment vessels (which do add weight and reduce effective payload, but the total lift may still be worth the cost)