It’s been almost 80 years since the first atomic bomb was detonated, and scientists say there’s still much to learn about how nuclear devices function as they reach the point of exploding.

The estimated 1,054 explosive tests conducted in the U.S. before they were banned in 1992 and the 33 subcritical or non-explosive tests done since 1997 have given scientists a good idea of what works.

But being able to analyze precisely how the bombs worked is a different matter.

Los Alamos National Laboratory teams are assembling components for a giant, high-tech machine that researchers say will give them a much more detailed look at what happens as a nuclear device approaches criticality — a self-sustaining nuclear chain reaction that releases high amounts of heat and radiation.

In particular, the machine, dubbed Scorpius, will provide greater insight into plutonium, the essential ingredient in detonating a nuclear device.

“Plutonium is a weird material,” said Mike Furlanetto, a lab scientist and the project’s director. “We understand it well enough to be confident our [nuclear] stockpile works, but there are a lot details where it’s sort of mysterious. So this will be a new window into how it behaves.”

The $1.8 billion project will aid in stockpile stewardship, a program designed to ensure the safety and reliability of the nation’s nuclear weapons without the use of underground explosive testing.

Testing for the stockpile is now conducted using computer simulations, which draw from data collected from past nuclear tests, and through subcritical experiments, which measure the plutonium’s viability without pushing a device to criticality. Scorpius will offer technological improvements to those experiments.

Scorpius is scheduled to begin operating in 2030, Furlanetto said, noting it’s an immense undertaking to bring a machine of this magnitude online.

The machine will be housed 1,000 feet underground at the Nevada National Security Site, formerly known as the Nevada Test Site, and will have a 400-foot-long accelerator, made up of 102 cells, that will generate radiographic images of the experiments.

How it essentially works: An injector will send high-energy electron beams in four or more pulses down the accelerator, with each of the cells boosting the pulsing energy, which then collides with metal targets, producing X-rays.

The X-rays are converted into images recorded by a high-speed camera.

Capturing a series of images of plutonium approaching criticality will create a fuller picture of the phenomenon than the single images taken now, Furlanetto said.

The technology also can read how larger amounts of plutonium act at more extreme temperatures and pressure, he said, crediting the machine’s sheer size and power with offering researchers a glimpse into something new.

Previously, they were limited to smaller quantities of plutonium, he said. “We didn’t have a tool like this accelerator that could see through a big chunk of plutonium at very extreme conditions.”

Taking radiographs of plutonium at these more intense conditions will provide more accurate data for computer simulations, he added.

Building the accelerator is part of a larger effort to improve subcritical tests. The National Nuclear Security Administration, which oversees the nuclear weapons stockpile, is funding both Scorpius and Zeus, a machine that will measure the rate of the nuclear chain reaction.

The Los Alamos lab is collaborating with the Nevada National Security Site as well as the Lawrence Livermore and Sandia national labs on Scorpius. Livermore is developing the pulse-power systems, and Sandia is supplying the device that injects the electron beams.

Los Alamos lab crews are building six cells that will be housed in two modules, with the work expected to be completed by the end of the year.

Each module is a 100-square-foot vacuum chamber with magnets, power connection, vacuum pumps, cooling water and controls that must be precisely aligned.

The lab will deliver the finished cell modules to Nevada to be tested. A vendor then will build the other 96 cells at that site.

The more sophisticated testing will allow the lab to ensure the new plutonium pits it plans to manufacture to equip warheads will be effective — and whether any adjustments in design or shape will be needed, Furlanetto said.

“This is a test that will give us more confidence,” he added.

Scorpius also will provide valuable information about plutonium’s aging, he said.

A big reason the lab is working toward producing 30 fresh plutonium cores is some federal scientists and nuclear security officials contend the Cold War pits have grown too old to be reliable, partly because of radioactive decay.

JASON, an independent group of scientists that advises the federal government, has said the legacy pits may be good for decades longer than the government estimates, so there may be no need to fashion new ones. At the least, more research is required, the group argues.

Scorpius could settle that debate, though the pits will be at least five years older by the time it’s operating.

“So if ... aging plutonium behaves differently from new plutonium, we want to measure what that change is and make sure it’s understood,” Furlanetto said.

Another innovative feature will be how flexible the machine will be, Furlanetto said. Technicians will be able to quickly modify the energy pulses’ size, number or trajectory.

In the past, an accelerator was locked into particular settings, forcing scientists to work experiments around the machine, he said.

“It’s really going to be a big step forward in accelerator science, which is pretty cool,” Furlanetto said.