Most advances in inertial fusion energy (IFE) had their root in DoE nuclear deterrence programs, from NIF to the Z Machine
From 1945 until 1992, the United States performed 1,054 nuclear weapons tests, including 215 atmospheric and underwater tests, to validate the design and manufacture of the US nuclear weapons stockpile. Other than the first 30 of those tests which were fission-type (uranium- or plutonium-fueled), by far most of these tests (1,024) were thermonuclear weapons tests, employing “H-bombs” harnessing fusion energy. Since the signing of the Comprehensive Nuclear Test Ban Treaty in 1992, the United States has relied on theoretical and experimental work (other than full-scale detonation of nuclear weapons) to validate the US nuclear weapons stockpile (Also known as the Stockpile Stewardship Program), much of which has led to the progress that the US (and others) have made in commercial fusion energy. In this article, The Fusion Report examines the positive effect that these efforts have had on the US commercial fusion energy program.
The Basics of Thermonuclear Weapons
Before we get into why it is important to test thermonuclear weapons and/or the mechanisms that make thermonuclear weapons possible, let’s look into the basics of how thermonuclear weapons operate. As a disclaimer, all the information presented here is from public sources, including Wikipedia and government websites. As such, no classified or sensitive information has been utilized in the writing of this article, and the authors are not involved or have access to any classified nuclear weapons information.
Thermonuclear weapons (also known as fusion weapons, hydrogen bombs, or H-bombs) are known as ‘second-generation’ weapons (fission devices are known as ‘first-generation’ weapons), which employ nuclear fusion for their destructive force. The design of all thermonuclear weapons are believed to be of the Teller–Ulam configuration, named after physicists Edward Teller and Stanislaw Ulam. The design utilizes radiation implosion, in which X-rays from the detonation of the primary stage (a small plutonium fission device), are channeled to compress a separate fusion secondary stage containing thermonuclear fuel (primarily lithium-6 deuteride). During detonation, the fission neutrons convert lithium-6 to helium-4 plus tritium. The deuterium and tritium then undergo a reaction that releases energy and fast neutrons. Additionally, most weapons use a natural or depleted uranium tamper and case. This undergoes fast fission from fast fusion neutrons, and is the main contribution to the total yield and radioactive fission product fallout (Wikipedia article on Thermonuclear Weapons).
Why Testing the Mechanics of Thermonuclear Weapons is Important
Unlike bullets, which can last unfired from between 10-40 years stored in good cool/dry conditions, thermonuclear weapons are complex mechanisms that do not necessarily age well over time (a US W88 thermonuclear warhead, first designed in the 1970s and used in the US Navy Trident submarine launched ballistic missile, is shown in the illustration above for reference). Nearly all contemporary thermonuclear devices utilize a plutonium ‘hollow pit’ in their primary, increasing neutron production in the primary and allowing its size and mass to be significantly reduced. For example, one of the chief mechanisms of aging in a thermonuclear weapon is the decay of tritium over time, since tritium has a half-life of roughly twelve and a half years. Not only does this mean that the tritium must be replenished on a regular basis, but as it decays the effect of reduced tritium (and the byproducts that tritium decay produces) must also be modeled and tested. Many other mechanisms of thermonuclear weapons have similar potential ‘aging issues’.
Verifying the effectiveness and safety of America’s stockpile is the responsibility of the US Department of Energy (DoE) National Nuclear Security Administration (NNSA), which must do so annually. To put the NNSA’s work in perspective, the US nuclear stockpile is the smallest it has been since 1960. As of 2023, the stockpile stood at 3,748 warheads—a roughly 88 percent reduction in size since its peak of 31,255 warheads in the late 1960s. Most weapons in the current stockpile were produced during the 1970s and 1980s; at the time they were designed and built, these weapons were not designed or intended to last indefinitely. As such, the NNSA Stockpile Stewardship Program is responsible for ensuring the capabilities of the US nuclear deterrent. Comprising a wide range of scientific activities from modeling and simulation to subcritical nuclear experiments, the NNSA’s programs allow them to assess and certify the stockpile.
It is also for this reason that the NNSA funds high-energy density science facilities that fusion people know well: the Lawrence Livermore National Laboratory National Ignition Facility (NIF), the Sandia National Laboratories Z-Machine, and the University of Rochester Omega Laser Facility. These facilities conduct research not only into the safe aging of nuclear weapons components, but also modernizing of nuclear weapons designs, including performing simulations of the weapon updates via numerical analyses on NNSA super-computers, and high-energy experiments as needed.
The Value to Commercial Inertial Fusion of Modernizing the NNSA
One of the biggest issues of all three facilities is that they’re old. NIF is seventeen years old, having been certified as complete on March 31st of 2009. The Sandia Z machine is even older, having been modified into its current state thirty years ago in 1996. Similarly, the current iteration of the Omega laser facility in its 60-beam configuration was commissioned in 1995 and is 31 years old. In all three cases, not only are their facilities old, but the architecture of their lasers and Marx generators are old as well, and probably obsolete by today’s standards. There are solutions with more efficient lasers and more exchangers are available from commercial fusion energy developments.
Commercial ICF companies and the NNSA could accelerate the development of commercial fusion while jointly accelerating nuclear weapons stewardship through a well-thought out joint program. This is incredibly important when you consider that we are competing with China both on fusion energy and on nuclear security. Contemporary ICF companies are relatively young and could use the funding if it was made available in the right situation. A recent paper by The Hudson Institute defines a reasonable set of plans and milestones for such a program, though its focus needs to increase to increase the value to commercial ICF as well as to nuclear deterrence. While the missions of commercial fusion energy companies in that of the NNSA are different, they can still accomplish both goals if our government and business leader shows some imagination and incentivize the right behaviors.
