Editing Manhattan Project (section)

=== Hanford reactors ===
{{Main|Hanford Engineer Works}}
Although an air-cooled design was chosen for the reactor at Oak Ridge to facilitate rapid construction, this was impractical for the much larger production reactors. Initial designs by the Metallurgical Laboratory and DuPont used helium for cooling, before they determined that a water-cooled reactor was simpler, cheaper and quicker to build.<ref>{{harvnb|Groves|1962|pp=78–82}}.</ref> The design did not become available until 4 October 1943; in the meantime, Matthias concentrated on improving the Hanford Site by erecting accommodations, improving the roads, building a railway switch line, and upgrading the electricity, water and telephone lines.<ref>{{harvnb|Jones|1985|p=210}}.</ref>

[[File:Hanford B-Reactor Area 1944.jpg|thumb|left|Aerial view of Hanford [[B-Reactor]] site, June 1944|alt=An aerial view of the Hanford B-Reactor site from June 1944. At center is the reactor building. Small trucks dot the landscape and give a sense of scale. Two large water towers loom above the plant.]]
As at Oak Ridge, the most difficulty was encountered while canning the uranium slugs, which commenced at Hanford in March 1944. They were [[pickling (metal)|pickled]] to remove dirt and impurities, dipped in molten bronze, tin, and [[silumin|aluminum-silicon alloy]], canned using hydraulic presses, and then capped using [[arc welding]] under an argon atmosphere. Finally, they were tested to detect holes or faulty welds. Disappointingly, most canned slugs initially failed the tests, resulting in an output of only a handful per day. But steady progress was made and by June 1944 production increased to the point where it appeared that enough canned slugs was available to start [[B-Reactor|Reactor B]] on schedule in August 1944.<ref>{{harvnb|Hewlett|Anderson|1962|pp=222–226}}.</ref>

Work began on Reactor B, the first of six planned 250&nbsp;MW reactors, on 10 October 1943.<ref>{{harvnb|Thayer|1996|p=139}}.</ref> The reactor complexes were given letter designations A through F, with B, D and F sites developed first, as this maximized the distance between the reactors. They were the only ones constructed during the Manhattan Project.<ref>{{harvnb|Hanford Cultural and Historic Resources Program|2002|p=1.16}}</ref> Some {{convert|390|ST}} of steel, {{convert|17400|cuyd}} of concrete, 50,000 concrete blocks and 71,000 concrete bricks were used to construct the {{convert|120|ft|m|adj=on}} high building.

Construction of the reactor itself commenced in February 1944.<ref>{{harvnb|Hewlett|Anderson|1962|pp=216–217}}.</ref> Watched by Compton, Matthias, DuPont's [[Crawford Greenewalt]], [[Leona Woods]] and Fermi, who inserted the first slug, the reactor was powered up beginning on 13 September 1944. Over the next few days, 838 tubes were loaded and the reactor went critical. Shortly after midnight on 27 September, the operators began to withdraw the [[control rod]]s to initiate production. At first all appeared well but around 03:00 the power level started to drop and by 06:30 the reactor had shut down completely. The cooling water was investigated to see if there was a leak or contamination. The next day the reactor started up again, only to shut down once more.<ref>{{harvnb|Hewlett|Anderson|1962|pp=304–307}}.</ref><ref name="Jones, pp. 220-223">{{harvnb|Jones|1985|pp=220–223}}.</ref>

Fermi contacted [[Chien-Shiung Wu]], who identified the cause of the problem as [[neutron poison]]ing from [[xenon-135]], which has a [[half-life]] of 9.2 hours.<ref>{{harvnb|Howes|Herzenberg|1999|p=45}}.</ref> Fermi, Woods, [[Donald J. Hughes]] and [[John Archibald Wheeler]] then calculated the [[nuclear cross section]] of xenon-135, which turned out to be 30,000 times that of uranium.<ref>{{harvnb|Libby|1979|pp=182–183}}.</ref> DuPont engineer George Graves had deviated from the Metallurgical Laboratory's original design in which the reactor had 1,500 tubes arranged in a circle, and had added an additional 504 tubes to fill in the corners. The scientists had originally considered this overengineering a waste of time and money, but Fermi realized that by loading all 2,004 tubes, the reactor could reach the required power level and efficiently produce plutonium.<ref>{{harvnb|Thayer|1996|p=10}}.</ref> Reactor D was started on 17 December 1944 and Reactor F on 25 February 1945.<ref name="Thayer 1996 141">{{harvnb|Thayer|1996|p=141}}.</ref>