The NRU reactor at Chalk River Laboratories of AECL Research, has provided intense neutron beams since it began operation in 1957. The reactor uses D2O as both moderator and coolant and operates at 125 MW. It presently uses 93% enriched fuel. It has a large core contained in a vessel that is 12 ft in diameter and 10 ft high. The core contains ninety fuel sites and has eight reactor loops and thirty isotope irradiation sites. It also has beam tubes, seven of which are for neutron scattering instruments and one for neutron radiography. The on-line fueling capability of NRU means the reactor does not operate on a fixed-fueling cycle. Rather, shut-downs are scheduled as required by the scientific, engineering or maintenance needs.