DIDO was a materials testing nuclear reactor at the Atomic Energy Research Establishment at Harwell, Oxfordshire in the United Kingdom.
It used enriched uranium metal fuel, and heavy water as both neutron moderator and primary coolant.
DIDO was designed to have a high neutron flux, largely to reduce the time required for testing of materials intended for use in nuclear power reactors.
In all, six DIDO class reactors were constructed based on this design: HIFAR was the last to shut down, in 2007.
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