EBR-I, shown in Fig. 4.38 in cutaway form, was a 1 MWt reactor built in 1948. It was composed of 0.5-in. diameter pins of enriched 235U in a single big assembly which formed the entire 8-in. diameter core. Cooling was provided by NaK at 6 ft/sec increasing in temperature from 250 to 350°C. The vessel and piping were all doubly contained, top inlet being provided

to the vessel, going down through the blanket, and up through the core. The coolant was pumped by EM pumps. Control was provided by bottom operated rods and reflectors for fast control with a movement of the 5 ton bottom blanket to provide slow control. This latter control suffered from poor clearances.