Later operation
On 12 December 1942, CP-1's power output was increased to . Lacking shielding of any kind, it was a radiation hazard for everyone in the vicinity, and further testing was continued at 0.5 W. Operation was terminated on 28 February 1943, and the pile was dismantled and moved to Site A in the Argonne Forest, now known as Red Gate Woods. There the original materials were used to build Chicago Pile-2 (CP-2). Instead of being spherical, the new reactor was built in a cube-like shape, about tall with a base approximately square. It was surrounded by concrete walls thick that acted as a radiation shielding, with overhead protection from of lead and of wood. More uranium was used, so it contained of uranium and of graphite. No cooling system was provided as it only ran at a few kilowatts. CP-2 became operational in March 1943, with a k of 1.055. During the war, Walter Zinn allowed CP-2 to be run around the clock, and its design was suitable for conducting experiments. CP-2 was joined by Chicago Pile-3, the first heavy water reactor, which went critical on 15 May 1944.
The Red Gate Woods later became the original site of Argonne National Laboratory, which replaced the Metallurgical Laboratory on 1 July 1946, with Zinn as its first director. CP-2 and CP-3 operated for ten years before they outlived their usefulness, and Zinn ordered them shut down on 15 May 1954. It read as follows: