US lab sets up new supercomputer to test nuclear stockpile

It is expected to deliver performance up to eight times faster than its predecessor.
Ameya Paleja
Crews install Crossroads components at the Lab's Strategic Computing Complex.
Crews install Crossroads components at the Lab's Strategic Computing Complex.


The Los Alamos National Laboratory (LANL) is in the final stages of setting up a new supercomputer dubbed Crossroads that will allow it to test the US nuclear stockpile without major tests, a press release said. The system has been supplied by Hewlett Packard and installation began in June of this year.

The Department of Energy (DoE) has been tasked with the responsibility of ensuring that the US nuclear stockpile can be relied upon if and when it needs to be used. For this purpose, the federal agency does not actually test the warheads but carries out simulations to determine the storage, maintenance, and efficacy of the weapons.

Crossroads is the third supercomputer in the Advanced Technology Systems (ATS) deployed to help carry out these simulations. The first in the series, Trinity (ATS-1), was also installed at LANL, while the second in the series, Sierra (ATS-2), was installed at Lawrence Livermore National Laboratory (LLNL).

Not focused on exaFLOPS

The Trinity system was installed in 2015 and boasted a computing prowess of 41.46 petaFLOPS. For its successor at LANL, though, the team wasn't keen on the exaFLOP benchmark most supercomputers are trying to breach these days.

Instead of trying to pack the system with graphic processing units (GPUs), the team focused on memory size and memory access, which are crucial to solving the problems faced during simulations.

The system has been supplied by the Hewlett Packard Enterprise Cray Division, which has also delivered other supercomputers around the world. The assembly began in June this year, and the system is now in the final stages of being put together.

Initial tests suggest that Crossroads will be able to deliver over four to eight times the efficiency of the Trinity system. This is made possible by the high-bandwidth memory that brings memory directly to the chip for processing and allows for quicker data transfers between CPU and memory.

US lab sets up new supercomputer to test nuclear stockpile
Crews deliver Crossroads components to the Lab's Strategic Computing Complex.

“It hardly ever happens in computing that you can move to a new system and see huge gains without changing the codes,” said Gary Grider, leader of the High Performance Computing Division at LANL. “But the switch from Trinity to Crossroads will do just that.”

Supercomputer subsystems

Crossroads isn't just one massive computer but also comprises three smaller supporting subsystems called Rocinante, Razorback, and Tycho, each tasked to perform a particular function.

Although data about the nuclear stockpile simulations are highly secretive, the code used to carry them out is not necessarily developed in classified environments. Code developers need access to Crossroads architecture at a smaller scale in an application regression system. This role is played by Rocinate.

Razorback is a similar test bed but for system administrators who can prepare and test upgrades and patches on a smaller system before applying them to the main machine.

Tycho, named after a spacecraft from the science fiction series The Expanse, had the same architecture as Crossroads but featured a more conventional memory. The system is now available for three national laboratories under DoE: the LLNL, LANL, and Sandia National Laboratory.

Even as Crossroads is preparing to come online for the three laboratories this fall, the next iterations, El Captain (ATS-4) to be installed at LLNL and unnamed ATS-5, are already in the works, the news release stated.

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