The US is spending another $600 million to build its third "exascale" supercomputer, which will be focused on simulating nuclear explosions.

On Tuesday, the Department of Energy announced "El Capitan," a machine designed to achieve 1.5 exaflops, or 1.5 quintillion calculations per second. The processing power will dwarf the capabilities of the top 100 supercomputers combined when it's completed in late 2022 at the Lawrence Livermore National Lab in California.

El Capitan will have a special mission: It'll conduct classified experiments to ensure that the US's nuclear weapons arsenal remains in good working order.

The US government is building the supercomputer to serve the National Nuclear Security Administration (NNSA), the federal agency charged with maintaining the country's nuclear weapons stockpile. In 1992, the US conducted its last live nuclear test, and since then, the country has relied on supercomputers to carry out the detonations virtually.

But creating an accurate simulation isn't easy; it requires a vast amount of computing power when you're trying to predict how a nuclear explosion will unfold at a molecular level. A 3D simulation, as opposed to a 2D simulation, needs even more processing power. The world's second fastest supercomputer, Sierra, is routinely simulating such tests, but at under 0.125 exaflops. In contrast, the upcoming El Capitan system is expected to be about ten times faster.

"It will give us answers about the nuclear stockpile more accurately and more quickly than ever before," Bill Goldstein, director at the Lawrence Livermore National Laboratory, told journalists in a press call.

Specifically, El Capitan promises to help scientists and weapon designers come up with new materials and components to keep the US's nuclear arsenal safe and operational. "Virtually every component to the warhead and delivery systems must be redesigned and remanufactured to maintain the same capabilities we had in 1992," Goldstein added.

To build the exascale supercomputer, the US government has hired high-performance computing vendor Cray. El Capitan will incorporate both CPUs and GPUs into the architecture. However, Cray is still determining which chip vendors, such as Intel, AMD and Nvidia, will supply the silicon to the upcoming supercomputer.

Running El Capitain will also require a lot of electricity. Goldstein said he expects it may end up using as much as 30 megawatts of power, which is more than twice as much electricty as the world's current fastest supercomputer, Summit.

Outside of nuclear testing, El Capitan will be used for research related to national security, including protecting critical infrastructure. Once the supercomputer is completed, it's scheduled to start conducting the nuclear research in 2023.

The US's two other exascale supercomputers, Frontier and Aurora, will arrive earlier in 2021. Combined all three machines will cost an estimated $1.7 billion to build. But the US isn't alone in trying to create an exascale computer. China is also developing its own exascale machines, which could also start arriving in 2021.