Nuclear Furnace 1 was a nuclear reactor designed and built as part of the Rover program specifically to test advanced fuel elements with (U,Zr) carbon-graphite composite fuel with ZrC (see zirconium and carbide) coating for use in nuclear space propulsion. The test was the first to be conducted in a closed cycle to control radioactive emissions – all previous tests in the Rover program having been open-cycle, exhausting into the atmosphere.

Nuclear Furnace 1 (NF-1) was tested in July 1972 and achieved 44 megawatts of power for 6,528 seconds. Other reactors developed during the Rover program were KIWI, Phoebus, and Pewee-1.