| Tory II-C | |
|---|---|
 Tory-IIC nuclear ramjet | |
| Reactor concept | homogeneous |
| Location | Jackass Flats |
| Coordinates | 36°48′59″N 116°9′52″W / 36.81639°N 116.16444°W |
| Main parameters of the reactor core | |
| Fuel (fissile material) | highly enriched uranium oxide |
| Fuel state | solid |
| Neutron energy spectrum | slow |
| Primary control method | Boron control drums |
| Primary moderator | Beryllium oxide |
| Primary coolant | air |
| Reactor usage | |
| Primary use | propulsion |
| Power (thermal) | 600 MW |
| Criticality (date) | 20 May 1964 |
| Operator/owner | Lawrence Radiation Laboratory |
Project Pluto was a United States government program to develop nuclear-powered ramjet engines for use in cruise missiles. Two experimental engines were tested at the Nevada Test Site (NTS) in 1961 and 1964 respectively.
On 1 January 1957, the U.S. Air Force and the U.S. Atomic Energy Commission selected the Lawrence Radiation Laboratory to study the feasibility of applying heat from a nuclear reactor to power a ramjet engine for a Supersonic Low Altitude Missile. This would have many advantages over other nuclear weapons delivery systems: operating at Mach 3, or around 3,700 kilometers per hour (2,300 mph), and flying as low as 150 meters (500 ft), it would be invulnerable to interception by contemporary air defenses and carry more and larger nuclear warheads (up to sixteen with nuclear weapon yields of up to 10 megatonnes of TNT (42 PJ)) and deliver them with greater accuracy than was possible with intercontinental ballistic missile (ICBMs) at the time and, unlike them, could be recalled.
This research became known as Project Pluto, and was directed by Theodore Charles (Ted) Merkle, leader of the laboratory's R Division. Originally carried out at Livermore, California, testing was moved to new facilities constructed for $1.2 million on 21 square kilometers (8 sq mi) at NTS Site 401, also known as Jackass Flats. The test reactors were moved about on a railroad car that could be controlled remotely. The need to maintain supersonic speed at low altitude and in all kinds of weather meant that the reactor had to survive high temperatures and intense radiation. Ceramic nuclear fuel elements were used that contained highly enriched uranium oxide fuel and beryllium oxide neutron moderator.
After a series of preliminary tests to verify the integrity of the components under conditions of strain and vibration, Tory II-A, the world's first nuclear ramjet engine, was run at full power (46 MW) on 14 May 1961. A larger, fully-functional ramjet engine was then developed called Tory II-C. This was run at full power (461 MW) on 20 May 1964, thereby demonstrating the feasibility of a nuclear-powered ramjet engine. Despite these and other successful tests, ICBM technology developed quicker than expected, and this reduced the need for cruise missiles. By the early 1960s, there was greater sensitivity about the dangers of radioactive emissions in the atmosphere, and devising an appropriate test plan for the necessary flight tests was difficult. On 1 July 1964, seven years and six months after it was started, Project Pluto was canceled.