The problem is shielding all of the people. When you land the plane all of that ionizing radiation bounces back at the people inside giving bathing them in fata

The problem is shielding all of the people. When you land the plane all of that ionizing radiation bounces back at the people inside giving bathing them in fatal or near fatal levels. The shielding is just too heavy and the physics of shielding make it very unlikely we can develop anything lighter. Also should the plane have an accident you now have radioactive material spread over miles. Which is also not an easily solved problem.