What are Subcritical Experiments?

Subcritical experiments are designed to mimic key aspects of a nuclear weapon’s fission stage without triggering a self-sustaining nuclear chain reaction. Researchers detonate high explosives around a small sample of plutonium – typically less than eight ounces – contained within a robust steel vessel. This controlled detonation allows scientists to observe how plutonium behaves under extreme pressure, providing invaluable data for assessing weapon performance. As explained in a 2021 Cipher Brief column, the process relies heavily on advanced computer simulations to extrapolate findings and predict behavior in real-world scenarios.

The Evolution of Stockpile Stewardship

The focus of these experiments has evolved over time. Initially, the primary goal was to reduce uncertainties in the performance of existing weapons, particularly as the U.S. adhered to the moratorium on full-scale nuclear testing. However, with the development of new warheads like the W93 – slated for deployment on U.S. submarines by 2040 – subcritical experiments are now also crucial for validating designs that rely on previously tested components. The NNSA has stated that the W93 “will not require additional nuclear testing,” highlighting the confidence placed in the subcritical testing program and advanced modeling capabilities.

The U.S. isn’t alone in conducting these tests. Russia has reportedly carried out at least 25 subcritical experiments at its Novaya Zemlya test site, while the U.S. has completed 34 at the Nevada Test Site as of May 2024. These activities occur within the framework of the 1996 Comprehensive Nuclear Test Ban Treaty (CTBT), which prohibits “any nuclear weapon test explosion or any other nuclear explosion,” but explicitly allows for subcritical experiments.

Recent Developments and Presidential Statements

Recent statements by former President Trump have injected uncertainty into the discussion surrounding nuclear testing. His claims regarding the need to “test our Nuclear Weapons on an equal basis” with other nations sparked confusion and prompted varied responses from his own administration. These statements even appeared to encourage Russia to consider resuming full-scale testing, leading to a Kremlin meeting where Russian national security officials discussed the possibility.

The ambiguity surrounding Trump’s remarks – whether he referred to delivery systems or warheads themselves – fueled further debate. While some officials suggested he was referring to system tests, others interpreted his words as a potential return to explosive testing. Energy Secretary Chris Wright clarified that any planned tests would be “non-critical explosions” focused on new systems, leveraging the nation’s advanced simulation capabilities. He emphasized that the U.S. possesses a significant advantage in nuclear weapons design due to decades of prior testing and sophisticated modeling.

Despite the rhetoric, the current schedule at LANL indicates subcritical experiments are planned through 2032. This ongoing commitment suggests a continued reliance on this method for maintaining the integrity of the U.S. nuclear stockpile. But what does this mean for the future of arms control and international security? And how will the U.S. balance the need for a credible deterrent with the desire to avoid escalating tensions with Russia and China?

The debate surrounding nuclear testing underscores the complex challenges facing the U.S. in the 21st century. Maintaining a safe, secure, and reliable nuclear deterrent requires a delicate balance of scientific innovation, strategic planning, and international diplomacy.

Frequently Asked Questions About Subcritical Experiments

• What is the primary purpose of subcritical experiments?

  The main goal of subcritical experiments is to evaluate the behavior of nuclear materials under conditions similar to a nuclear detonation, without actually creating a nuclear explosion. This helps ensure the safety and reliability of existing and future nuclear weapons.

• Are subcritical tests allowed under the Comprehensive Nuclear Test Ban Treaty?

  Yes, the CTBT specifically allows for subcritical experiments, as they do not involve a self-sustaining nuclear chain reaction and therefore do not constitute a “nuclear weapon test explosion.”

• How does the U.S. use subcritical experiments to develop new warheads like the W93?

  The W93 utilizes components based on previously tested designs. Subcritical experiments help validate the performance of these components and ensure the new warhead meets safety and security requirements without requiring a full-scale nuclear test.

• What is the difference between a subcritical test and a full-scale nuclear test?

  A full-scale nuclear test involves detonating a complete nuclear weapon, resulting in a nuclear explosion. A subcritical test uses high explosives to compress a small amount of plutonium, but does not achieve criticality and therefore does not produce a nuclear explosion.

• Why is there concern about Russia and China potentially increasing their nuclear testing activities?

  Increased testing by other nations could lead to an arms race and undermine the global non-proliferation regime. It also raises concerns about the development of new and more dangerous nuclear weapons.