US President Donald Trump announced the resumption of nuclear tests. Russian President Putin immediately responded in a similar way. What does this mean from a technical point of view? Will there be nuclear explosions again?
On July 16, 1945, at 5:30 in the morning, a powerful explosion shook the New Mexico desert. The shock wave spread up to 160 kilometers, and the cloud, rising to a height of 12 kilometers, was visible for hundreds of kilometers. This was the first test of a nuclear weapon in human history. In the following decades, the United States conducted over 1,000 other tests – initially in the atmosphere, and after the 1960s only underground - until the US Congress banned all nuclear tests in 1992.
Four years later, the Comprehensive Nuclear-Test-Ban Treaty (CTBT) was drafted, which the US and several other countries signed but never ratified. That is why, nearly 30 years later, the treaty has still not entered into force. However, the world has largely adhered to it throughout the 21st century - with the exception of North Korea, no other country has conducted nuclear tests since 1998.
Underground nuclear tests are unlikely
A few days ago, a publication by US President Donald Trump caused a stir after he accused “other countries“ of maintaining “nuclear testing programs“, and announced that because of this, the US would immediately resume nuclear weapons testing. Could this be referring to underground detonations of warheads?
There are some inaccuracies in Trump's publication. It is not the US, but Russia, that maintains the largest nuclear arsenal in the world. Furthermore, the US Department of Energy, not the Pentagon (now renamed the “Department of War“), is responsible for maintaining and managing this arsenal. Its head, Chris Wright, was quick to clarify to Fox News that these are “system tests, not nuclear explosions.” The focus would be on new weapons delivery systems and “other nuclear weapon components,” but not warheads. But is that exactly what the president wants?
The problem: aging nuclear weapons
During the decades of the moratorium, the United States has not stopped maintaining the infrastructure necessary for nuclear testing. In addition to several research laboratories, the Department of Energy still manages the “Nevada National Security Site” (NNSS). More than 900 underground nuclear tests have been conducted there, although the last one was 33 years ago. According to the Washington-based Center for Strategic and International Studies, an underground nuclear detonation would not be possible “immediately” or “within a few months“, and at the earliest in three years.
Not only the United States, but all nuclear powers are faced with the challenge of modernizing and maintaining their arsenals without resorting to nuclear explosions. To this end, in the 1990s, the “Arsenal Monitoring Program” was created in Washington, which costs billions of dollars a year. About 27,500 employees feed countless data from nuclear tests of the 20th century into super-powerful supercomputers in order to simulate as accurately as possible how individual components would behave in an explosion.
Russia and the United States each have over 5,000 nuclear warheads. Many of them have been stored in highly secured warehouses for decades. But nuclear weapons also age: materials such as uranium-235 or plutonium-239 can oxidize or chemically decay, although these processes occur slowly. Batteries, electronic and mechanical components also wear out and must be replaced regularly. Therefore, an atomic bomb inevitably changes if it has been in storage for half a century.
At the limit of what is permitted: “subcritical” tests
To study these processes, the nuclear powers left a loophole when signing the Comprehensive Nuclear-Test-Ban Treaty: the conduct of so-called “subcritical nuclear tests”. Up to half a ton of chemical explosive containing a small amount of plutonium is detonated deep underground. The tests are called “subcritical” because the amount of plutonium does not reach the critical mass necessary for a self-sustaining chain reaction. They allow the behavior of plutonium to be studied, and the data obtained is used in computer simulations.
The Comprehensive Nuclear-Test-Ban Treaty does not specify exactly when an explosion qualifies as a “nuclear test“. A “subcritical test“ does not result in a measurable release of radioactive material into the environment and is therefore not explicitly prohibited. The United States has conducted at least 27 such tests, the last of which was officially recorded on December 5, 2012. It is believed that both China and Russia have conducted similar tests, although there is little information about when and how they were conducted. Because of their low power, these explosions are practically undetectable from the outside.
Want more tests?
Trump may want future tests in which the material would be brought to a self-sustaining chain reaction in controlled laboratory conditions. US State Department reports from 2020 and 2022 indicate that Moscow and Beijing have already conducted such tests. Trump may have been referring to these reports when he told CBS that Russia and China “are testing deep underground, and people don’t know exactly what’s going on.”
Whether such tests can even be conducted without the outside world noticing is debatable among experts. The Nuclear Test Ban Treaty has built hundreds of monitoring stations around the world precisely to prevent such scenarios.
However, Donald Trump may have something else in mind: testing weapons and delivery systems that could be equipped with nuclear warheads in a crisis. Over the past five years, China has built over 300 new silos for intercontinental ballistic missiles capable of reaching the United States in the event of war. Russia is not far behind – President Vladimir Putin tested similar delivery systems a few days ago, and now he says he does not rule out resuming nuclear tests. Russian Defense Minister Andrei Belousov said that given the recent statements and actions of the United States, it is “reasonable to immediately begin preparations for full-scale nuclear tests“