Just an idea how the shielding requirements can be reduced depending on the amount of radiation and safety requirements.
Basically if the reactors would be operated in flight only, special airports would be used and all other planes would be equipped with x-ray detectors then probably only the passenger side could be shielded.
Otherwise the shielding can be still reduced more than normal if the passengers and reactors are separated by wingspan.
Edit. Drawing:
http://imgur.com/vUx5D
It was a hell to paint it with mac trackpad
