Phoebus (nuclear reactors)

comparison of the KIWI and Phoebus reactors

Comparison of the KIWI and Phoebus assemblies.

Phoebus was a series of nuclear reactors, designed and built in the 1960s as part of the Rover program, to meet the needs of an interplanetary mission (see nuclear propulsion), in particular a manned mission to Mars. The design requirements were a thrust of 250,000 pounds, a specific impulse (Isp) of 840 second, and a reactor power level of 5,000 MWt.


The Phoebus-1 series was intended to study increasing the reactor power density and proved successful. When the power density was increased still further in the Phoebus-2 series, however, cooling of the aluminum pressure vessel was found to be a limiting factor. The Phoebus series demonstrated: 1) basic core and fuel configuration technology, 2) control of rocket parameters over a wide range of operating conditions, 3) the niobium carbide-molybdenum (NbC-Mo) coating could protect the fuel elements from hydrogen corrosion, 4) a two-pass regeneratively-cooled support structure allows full core performance, and 5) large nozzles for nuclear thermal rocket application were feasible. Other reactors developed during the Rover program were KIWI, Peewee-1, and Nuclear Furnace 1.


Phoebus series summary
project date max. power
burn time
Phoebus-1A Jun 25, 1965 1,090 630
Phoebus-1B Feb 23, 1967 1,450 1,800
Phoebus-2A Jun 26, 1968 4,082 750


Phoebus-2A performance parameters
reactor power (MWt) 4,082
flow rate (kg/s) 119.2
fuel exit temp (K) 2,283
chamber temp (K) 2,256
chamber pressure (MPa) 3.83
core inlet temp (K) 137
core inlet pressure (MPa) 4.73
reflector inlet temp (K) 68
reflector inlet pressure (MPa) 5.39
periphery & structural flow (kg/s) 2.3