Warning: Very wonky post, link, and subject matter
Since the United States signed, but did not ratify, the Comprehensive Nuclear Test Ban Treaty (CTBT) in 1996, it has held to a moratorium on nuclear explosive tests. The alternative to making sure nuclear weapons work and doing research to extend the understanding of their processes is a massive program called Stockpile Stewardship.
One of the activities under Stockpile Stewardship is investigate the properties of plutonium under the conditions just preceding a nuclear explosion. Plutonium is rapidly compressed by shaped explosives into a critical mass. What happens during that compression? Atoms are rearranged and smushed closer together. But plutonium has several solid phases that may affect that rearrangement.
The explanations in this interview are pretty good, but they dance around a lot of classification.
The facility is located far underground for physical and classification safety, but all that earth above provides shielding in case any of the subcritical experiments (no nuclear yield) transition to a hydronuclear experiment (with nuclear yield). We’re talking about amounts of energy that add only a tiny increment to the explosive or impact energy involved, not mushroom clouds. The CTBT specifies no nuclear yield, which is unverifiable, but a cudgel with which Republicans like to try to beat Russia with, as they did in the Trump administration.
Here’s the Pollux subcritical experiment, from 2012, to give you an idea of how innocuous an actual experiment can be. Setting one up, however, takes much more time.
I am a bit baffled by the size of what they’re building (football field), along with the need for two of something. The size might be explained by something like the Dual-Axis Radiographic Hydrodynamic Test Facility (DARHT) at Los Alamos, accompanied by perhaps other capabilities. The interview implies that something like this is being built.
Cross-posted to Nuclear Diner