Radiation shields include an outer composite wall, an inner composite wall, and an enclosed fuel chamber disposed between the inner and outer composite walls. A fuel may be contained within the enclosed fuel chamber. Spacecraft include one or more such radiation shields, and may further include a fuel cell and a conduit providing fluid communication between the fuel chamber of the radiation shield and the fuel cell. Methods of forming a radiation shield system include forming an enclosed fuel chamber between an outer composite wall and an inner composite wall of a radiation shield, and providing fuel within the enclosed fuel chamber.