Balanced maximum ATR full power distribution would be 50 MW in each lobe, but power shifting allows a maximum lobe power of 60 MW, a minimum lobe power of approximately 17 MW, and other lobes at powers in between. The major test spaces in the ATR are the nine flux trap positions. Five are equipped with independent test loops and four are used for drop-in capsules. Four of the independent test loops are pressurized water loops through which water circulates at pressures up to 2,500 psi. Sample capsules are also irradiated in vertical holes in the neck shim housing, center flux trap baffle, beryllium reflector, and racks located on the outside of the reflector.
Coolant flows down through the core.
Water enters the vessel through two 24-inch lines at the bottom, flows up outside cylindrical tanks that support and contain the core, passes through concentric thermal shields, and enters the relatively open upper part of the vessel. The water then flows down through the core to a flow distribution tank below the core and exits the vessel through four 18-inch lines. There are four primary coolant circulating pumps. Two or three pumps are operated, depending on the core power distribution. Three pumps yield a flow rate of approximately 49,000 gpm, and two pumps yield approximately 43,000 gpm.