Hanford's B Reactor, pivotal in the development of nuclear technology, occupies a footprint of 14 by 12 meters (1,750 sq feet) and is approximately five stories tall. The reactor core itself consisted of an 11-meter-tall (36 ft) graphite box measuring 8.5 by 11 meters (1,008 sq feet) and weighed 1,200 short tons (1,100 tons). It was penetrated horizontally through its entire length by 2,004 aluminum tubes and vertically by channels for the vertical safety rods.
The core is surrounded by a cast-iron thermal shield, enclosed on its top and sides by masonite and steel plates, forming a biological shield for radiation protection. The bottom of the thermal shield is supported by a 7-meter-thick (23 ft) concrete pad topped by cast-iron blocks. The graphite composition was selected to moderate the nuclear reaction fueled by 200 short tons (180 tons) of uranium slugs, each approximately the size of a roll of quarters. The slugs were sealed in aluminum cans and loaded into the aluminum tubes.