Nuclear materials may be hazardous if not properly handled or disposed of. Experiments of near critical mass sized pieces of nuclear material can pose a risk of a criticality accident. David Hahn serves as an excellent example of a nuclear experimenter who failed to develop or follow proper safety protocols. Such failures raise the specter of radioactive contamination.

Even when properly contained, fission by-products which are no longer useful generates radioactive waste, which must be properly disposed of. In addition, instruments exposed to nuclear materials may become radioactive, or become contaminated with nuclear waste.