During the Manhattan Project, scientists developing the first atomic devices came up with the idea to conduct nuclear and nonnuclear explosives tests inside steel containers. Today, this same approach is used for subcritical and hydrodynamic experiments that help maintain the United States’ nuclear stockpile.
The use of containers during the 1940s came from concerns about squandering weapons-grade plutonium, which was man-made and available in limited quantities. Scientists wanted to be able to recover the plutonium and reuse it if their experiments failed.
However, “no data existed on the subject, and the team faced numerous challenges,” writes Los Alamos National Laboratory engineer Jonathan Morgan in a paper titled “The Origins of Blast Loaded Vessels.”
The team constructed an assortment of small cast-steel spherical vessels, nicknamed Jumbinos. Explosives were detonated inside the vessels, many of which failed to contain the blasts. But even the failed tests had value; scientists used these to calculate how far fragments of a vessel might travel during a nuclear detonation.
The team also explored larger spherical containers, calling their first concept Jumbo #1. They also experimented with cylindrical containers, first testing explosions in barrel-shaped Jumbinos, then building Dumbo: a 6-foot-long cylinder that weighed 10 tons.
The next vessel, Jumbo #2 (and later simply Jumbo), was created to hold the Gadget, the first atomic device, which would be detonated at the Trinity site in southern New Mexico. Jumbo was a steel cylinder 10 feet in diameter and 25 feet long. With walls that were 14 inches thick, the entire device weighed 200 tons. In constructing this 12-million-dollar vessel, manufacturers “adopted cautious welding techniques that produced 100 percent flawless welds” that did not fail or crack, according to Morgan.
However, by the time Jumbo arrived at the Trinity site, scientists had decided not to use it. There were concerns that the thick vessel would prevent them from taking high-speed motion pictures and making other critical data measurements. So, instead of containing the Gadget, Jumbo helped scientists learn how a nuclear blast impacts an object. Morgan writes that Jumbo “was ready to take a beating unlike anything the world had ever seen.”
When the Gadget was detonated on July 16, 1945, “the heavy-duty tower holding the vessel was blown down, and yet Jumbo emerged unscathed—a testament to the strength and durability of the vessel,” Morgan writes.
A few months later, U.S. Army personnel used Jumbo to contain several simultaneous nonnuclear detonations. However, according to Morgan, Jumbo was not sealed correctly and was damaged. The vessel, now missing its ends, remains at the Trinity site today.
Two years later, in 1947, scientists at Los Alamos Scientific Laboratory (formerly Project Y of the Manhattan Project and later Los Alamos National Laboratory) once again found themselves in need of a vessel to contain explosives experiments. So, a third Jumbo vessel was built. For nearly two decades, scientists used Jumbo #3 to carry out high-explosives experiments.
Scientists considered using Jumbo #3 to house cameras on the PHERMEX (Pulsed High Energy Radiographic Machine Emitting X-Rays) project at the Lab. After building a road and transporting the cumbersome Jumbo #3 up the mesa to the site, the project was discontinued, and the vessel remains there today.
As researchers continued to conduct numerous open-air explosives tests at Los Alamos, they kept searching for a way to protect experiments from inclement weather and shield the surrounding forest from flying fragments and fire. In the mid-2000s, they turned to the idea of building smaller high-strength steel confinement vessels that could withstand a great deal of stress and absorb a significant amount of energy. Such vessels have been used since 2007 at the Lab’s Dual-Axis Radiographic Hydrodynamic Test (DARHT) facility, where two linear-induction accelerators produce high-powered x-ray images of materials that implode at more than 2.5 miles per second. Because the experiments conducted at DARHT do not contain special nuclear material (highly enriched uranium or weapons-grade plutonium), the vessels (which are 6 feet in diameter) are cleaned and reused.
Steel confinement vessels are also used for subcritical nuclear tests (tests that use small amounts of special nuclear material but do not create a self-sustaining nuclear reaction). These tests are designed by Los Alamos or Lawrence Livermore national laboratories and take place underground at the Nevada National Security Site (NNSS). After each test, the used vessels (which are 3 feet in diameter) are permanently sealed off, or entombed, in underground chambers. Data from these experiments is an essential part of stockpile stewardship, allowing for the maintenance of the nuclear weapons stockpile without full-scale nuclear testing.
Using confinement vessels also allows scientists to carry out safer and faster experiments, explains Joshem Gibson, a vessel engineer at the Lab. Now, the goal is to extend the life of existing multiuse vessels and produce new ones to meet increased testing needs. “With nearly 80 years of confinement vessel history, present day vessel engineers have a solid foundation to stand on as we continue to refine confinement vessel designs and add to the knowledge base,” Gibson says.
“It was a surprise for me to learn that confinement vessel design and use dated back to the Manhattan project,” says Ty Brooks, lead engineer for vessel procurement at Los Alamos. He adds that he has been inspired by the history and challenges of designing, creating, testing, and transporting the Jumbos.
The Lab’s last major procurement of vessels for both DARHT and NNSS was in 2004. Scientists are now working with production companies to fabricate new vessels and vessel components. Each vessel will cost approximately $2 million. As scientists move forward with these plans, they are also working with the U.S. Navy to explore improved materials and manufacturing processes. Brooks and Gibson say the goal is to develop higher-strength steel alloys that will allow for lighter, thinner, stronger vessels.
“The design and material of our current vessel is decades old,” Brooks says. “Although the design is great and has functioned well, we are always striving for improvements.” ★
