Answer to Question #4000 Submitted to "Ask the Experts"

At what facility was the plutonium for the Trinity nuclear device produced?

The first plutonium was manufactured at the Hanford Facility in Washington State. One reactor was the "B" reactor, and it produced plutonium for the first nuclear explosion (a test at the Trinity test site in Alamogordo, New Mexico) as well as for the weapon dropped on Nagasaki, Japan, on 9 August 1945, at the end of World War II. However, by the time the plutonium was being produced in sufficient quantities for the weapons, there were three 250-megawatt reactors running in production mode, two of which were being operated somewhat higher than their rated power levels to meet the demand. Even this produced only about a half pound of plutonium daily—about 250 grams.

Okay—so that's the simple answer. But a little more of the story is a lot more interesting!

First of all, nobody had ever seen plutonium when it was decided to develop nuclear weapons. Scientists had determined by calculations that plutonium would make a more effective weapon than uranium, but these calculations had not been tested. More importantly, however, is that plutonium is a separate chemical element than uranium. To make a uranium bomb required a lot of work because the uranium isotope that fissions nicely (²³⁵U) is very rare in nature, and it had to be concentrated by using a mechanical process such as gaseous diffusion or gas centrifuges. On the other hand, plutonium (once manufactured) could be chemically processed and removed that way; much more efficient.

Plutonium is made by bombarding uranium (specifically, ²³⁸U, which makes up virtually all of natural uranium) with neutrons. The best place to find neutrons is in a nuclear reactor core, so the Manhattan Project scientists realized they needed to build a reactor, and a fairly sizeable one, to crank out the plutonium needed for a weapon. Although very small amounts of plutonium can be found in nature, there simply is not enough of it. The first nuclear reactor, the one Fermi built in a squash court at the University of Chicago, proved that a nuclear reactor could work. Almost immediately after it was successfully operated, engineers and scientists began designing and building the plutonium production reactor at Hanford. To give you an idea of the audacity of this project, it's sort of like the Wright brothers building a WW II bomber as their second airplane.

The first plutonium was manufactured in a particle accelerator and Glenn Seaborg (codiscoverer of plutonium and one of a dozen Nobel Prize winners who participated in the Manhattan Project) was tasked with determining its chemical properties. Since the plutonium was being made an atom at a time, he had very small amounts to work with, usually invisible or nearly so. However, his work was completed, as was the production reactor at Hanford. As a result, the scientists at Los Alamos were able to perform the necessary tests, construct the first test bomb, and manufacture the weapon that was dropped on Nagasaki. Many of these tests were nuclear—the scientists were trying to determine what amount of plutonium they needed to form a critical mass. Many other tests were metallurgical and mechanical in nature—they were trying to find the best metal to alloy plutonium with so that it could be shaped into the core of a nuclear weapon, they were trying to discover how to work with a new and exotic metal, and they were learning how to process a metal that would not only heat up spontaneously from the heat of radioactive decay, but that would also spontaneously burst into flame in its pure form. It was quite a challenge, but obviously one that was overcome.

One other comment seems appropriate here. We often hear that "plutonium is the most deadly chemical known to man." Although plutonium is a toxic heavy metal, this statement is patently false. There are a number of toxins, including nerve agents and even toxins produced by mushrooms, that are far more lethal than plutonium. It is not harmless, but it really does not deserve the exaggerated concerns that are often raised.

For more information you can try one or more of the following references:

Closing the circle on the splitting of the atom. Department of Energy; January 1995.

Rhodes R. The making of the atomic bomb. New York, NY: Simon & Schuster, Inc.; 1995.

Seaborg GT. The plutonium story: The journals of Glenn T. Seaborg 1939-1946. Columbus, OH: Battelle Press; 1994

Serber R. The Los Alamos primer: The first lectures on how to build an atomic bomb. Berkeley, CA: University of California Press; 1992.

P. Andrew Karam, PhD, CHP