| Name | Lifetime | Building | Output | |
| GLEEP | 1947-1990 | H8 | 3kW |
Graphite Low Energy Experimental Pile
100kW graphite pile. First reactor built in Western Europe. Used for routine graphite and uranium quality testing, biological irradiation. Maintained as standard reference (at 3kW). Decommissioned 2005. |
| BEPO | 1948-1968 | H10 | 6MW |
British Experimental Pile Operation (or O for zero)
6MW graphite pile. First large reactor outside of North America and the USSR. Used for isotope production and as a general radiation source. Forerunner of all UK air and gas-cooled power reactors. |
| DIMPLE | 1954-1969 | B401.1 | 100W |
Deuterium Moderated Pile, Low Energy
Low power reactor used to examine different core arrangements. Transferred to Winfrith. |
| ZEPHYR | 1954-1958 | B401.1 | few watts |
Zero Energy Fast Fission Reactor
The first "fast" fission reactor built in the UK. Clad plutonium metal fuel rods surrounded by clad natural uranium rods. Also used to assess the breeding potential of Thorium-232. Decommissioned 1958. |
| ZETR | 1955-1957 | B351 | negligible |
Zero Energy Thermal Reactor
Used to study the physics of homogenous aqueous systems. Equipment transferred to Dounreay. |
| ZEUS | 1955-1957 | B401.4 | 100W |
Zero Energy Uranium System
100W unmoderated, uncooled, low energy fast fission breeder reactor built to obtain information for Dounreay reactors. Used highly enriched uranium surrounded by a natural uranium breeding blanket. The second Harwell fast reactor. Decommissioned 1957. |
| LIDO | 1956-1974 | B451 | 340kW | 340kW "swimming pool" reactor built for shielding studies. Used highly enriched uranium fuel with ordinary (light) water as a moderator and coolant. Decommissioned 1974-1995. |
| DIDO | 1956-1990 | B443 | 26MW |
Deuterium Oxide (D2O, heavy water)
26MW High flux heavy water moderated reactor. Used for isotope production, neutron physics, radiation chemistry, nuclear reactor material studies, neutron doping of silicon, neutron radiography. First of six similar "DIDO Class" reactors: PLUTO, DMTR (Dounreay), HIFAR (Lucas Heights), FRJ-2 (Julich) and DR 3 (Riso). |
| PLUTO | 1957-1990 | B775 | 26MW | 26MW High flux heavy water moderated reactor. Used for isotope production, neutron physics, radiation chemistry, nuclear reactor material studies, neutron doping of silicon. Pluto was the brother of Zeus and Neptune. |
| NEPTUNE | 1957-1959 | B451.3 | 100W | The Admiralty's low energy experimental reactor used to study behaviour of neutrons in water moderated core designs for submarine propulsion. Moved to Derby in 1963. Neptune was the brother of Zeus. |
| NERO | 1957-1959 | B401.4 | 100W |
New Experimental Reactor
Low energy reactor used to investigate physics design problems of graphite moderated reactors including sodium-cooled fast reactors. Transferred to Winfrith and renamed JUNO. |
| ZETA | 1957-1968 | H7 | fusion |
Zero Energy Thermonuclear Assembly
Demolished and work moved to Culham 2005/6. |
| HAZEL | 1958-1958 | B351 | 1W |
Homogenous Aqueous Zero Energy Level
Continuation of ZETR studies using Uranium-233, Uranium-235 and Plutonium solutions. Briefly considered as reactor type for OECD Project but eventually an alternative reactor design was chosen - DRAGON at Winfrith. Decommissioned in 1958. |
| DAPHNE | 1962-1967 | B451 | 100W |
DIDO and PLUTO's Handmaiden for Nuclear Experiments
Zero-energy heavy water moderated reactor designed as an auxiliary to DIDO and PLUTO. Highly enriched uranium-aluminium alloy. Decommissioned in 1967. |
| DELPHI | 1968-1968 | B451 | 100W | Conversion of DAPHNE as a model for a High Flux Beam Reactor. Enriched Uranium fuel. Used as planning rig for MTR in-pile experiments. Dismantled 1980. |
This list is based on information provided in 2010 by Ed Abel (Harwell Reactors Manager) and a list in Harwell: The Enigma Revealed by Nick Hance, published in 2006 and which is based in turn on an old poster currently in the shell of DIDO.
GLEEP
BEPO
DIDO
Cherenkov Radiation
ZETA
