Fission fragment rockets are nuclear reactors with a core consisting of thin fibers in a vacuum, and which use magnetic fields to extract the fission fragments from the reactor core. As an alternative to ordinary nuclear reactors, fission fragment rockets would have the advantages:

Approximately twice as efficient if one can directly convert the fission fragment energy into electricity;

By reducing the buildup of a fission fragment inventory in the reactor one could avoid a Chernobyl type disaster;

Collecting the fission fragments outside the reactor could simplify the waste disposal problem.