Nuclear weapons testing was once commonplace, but most countries have not done so for decades, following the adoption of the Comprehensive Nuclear-Test-Ban Treaty in 1996. Now that moratorium may be coming to an end. Politicians, including US President Donald Trump, have called for testing to resume.
The Comprehensive Nuclear-Test-Ban Treaty was signed but not ratified by the United States and some other holdouts, meaning the treaty did not enter into force. So far, however, most countries have complied with its provisions. The last nuclear test was carried out in 2017 by North Korea, the only country to have tested a weapon this century.
American scientists are currently certifying the capabilities of nuclear weapons using a variety of methods. computer experiments and simulations. As part of a program called Stockpile Stewardship, these studies prove that the weapons work – no nuclear detonation is necessary.
Watch the video to learn more about how nuclear weapons are understood scientifically and what a resumption of testing might entail.
Nuclear Weapons, Explained
Transcription
The United States has not tested a nuclear weapon since 1992, but that era of restraint may be about to end. President Donald Trump has said he wants the United States to resume nuclear testing, and the country has an aging nuclear arsenal and a massive modernization effort currently underway. The pressure to test is higher than it has been in decades.
Nuclear weapons are perhaps the most important thing you think about the least. They remain largely out of sight and out of mind in daily life. But if a major nuclear war breaks out, these weapons could cause unprecedented destruction. Such a war could directly kill hundreds of millions of people and disrupt Earth’s climate, causing widespread famine and billions more deaths.
Currently, the United States and Russia each possess more than 5,000 nuclear weapons. A handful of other countries have dozens or even hundreds of weapons. In my report for Scientific newsI explored the history of nuclear testing, the science of how these weapons are studied in the absence of testing, and what makes the physics behind nuclear explosions so complex.
And how a return to testing could have serious consequences on a global scale.
Between 1945 and the 1990s, countries around the world conducted more than 2,000 nuclear tests. But by the mid-1990s, nuclear testing had all but ceased, paving the way for a taboo on testing. The only country to have tested a nuclear weapon this century is North Korea. Nuclear weapons policies are based on deterrence. The idea is this: if your enemy knows that you have nuclear weapons and knows that they work, he will be deterred from attacking you for fear of devastating retaliation.
But if the United States or another country broke the testing taboo, others would likely follow. In short, testing by a single country could trigger a domino effect.
Nuclear weapons rely on two main types of nuclear reactions: fission and fusion. Fission is the splitting of large atomic nuclei. Fusion is the fusion of two small atomic nuclei into one. Nuclear explosions begin with fission. Each fission triggers other fissions in a self-sustaining chain reaction. In modern weapons, this fission helps trigger fusion reactions, greatly amplifying the energy released. In the age of testing, scientists detonated a weapon to ensure that fission and fusion reactions proceeded as expected.
When testing was phased out, scientists had to develop other methods to certify the weapons’ capabilities.
The United States now has a large program called Stockpile Stewardship, which combines sophisticated experiments and computer simulations to determine whether the weapons will work when needed. Some of the most secret experiments are taking place deep within the Nevada National Security Site, the same site where explosive nuclear weapons tests were once conducted.
These experiments are different from the explosive tests of the past. They are subcritical, meaning they do not produce a self-sustaining chain reaction or trigger a nuclear explosion. In a subcritical experiment, scientists study the material at the heart of these weapons: plutonium. In the United States, every nuclear weapon has a pit, a hollow sphere of plutonium. When a weapon detonates, the explosives implode the pit enough that it becomes critical, meaning it can host a self-sustaining fission chain reaction.
In a subcritical experiment, scientists also detonate plutonium with explosives, but not enough to cross this criticality threshold. They then study what’s happening inside the plutonium using X-ray imaging and other diagnostics. One of the biggest concerns that scientists are investigating in these experiments is how weapons age. The US stockpile consists of decades-old weapons. Scientists need to know whether they will work as expected or whether aging plutonium and other components could cause them to fail.
In the early days of nuclear weapons, testing was carried out on the surface, in the open air. This spread radioactive fallout, contaminating land and potentially sickening and displacing nearby populations.
To avoid such adverse effects, the tests were carried out underground. During underground testing, the fallout was largely contained in a cavity formed by the explosion deep below the surface, but occasional accidents could still harm people or the environment.
Nuclear testing on the surface or underground has now largely ceased. Subcritical experiments do not produce a nuclear explosion, so there is no contaminated cavity or risk of major radiation release.
Many scientists argue that subcritical experiments have given us a better understanding of nuclear weapons than in the testing era, making large-scale testing unnecessary. Others believe that while testing could improve our knowledge of the inner workings of these weapons, the risks far outweigh the benefits. A return to nuclear testing could trigger a new arms race and encourage countries without weapons to develop their own arsenals. And that, these scientists say, could bring the world closer to nuclear catastrophe.