The Vela incident, during which two nuclear explosions were recorded in the South Atlantic, can be called the most famous nuclear mystery.
This happened on September 22, 1979, and much was said that it could be a joint nuclear test of Israel and South Africa. 
However, apart from this incident, in the world of nuclear science there is no shortage of riddles and strange incidents.
10. The death of nuclear scientists in India and Iran
Over the past 10 years, the list of dead nuclear scientists in India has expanded significantly. While the authorities ignore this fact or speak of their deaths as something inexplicable, many local residents testify that the best representatives of their profession are killed, and under doubtful circumstances.

Two senior engineers from India’s first nuclear submarine were found dead on railroad tracks. It is believed that they were poisoned, however, their bodies were left on the rails so that death looked like suicide.

But the police came to a different conclusion. They dismissed the lawsuit, citing the fact that these are "two ordinary incidents."
Another nuclear scientist was strangled in a dream. Some of the investigators tried to attribute the incident to suicide, although there was a lot of evidence to prove that the murder was committed. However, no arrests were made.
Two other scientists were burned in their own laboratory, although they did not work with combustible materials when a fire broke out. One scientist was abducted by a group of armed people, but he managed to escape.

Again, the authorities were quick to dismiss all incidents. A parallel can be drawn with the death of Iranian nuclear scientists, who have attracted much more media attention.
Iranian scientists killed with car bombs. Government officials blame Israel, which categorically denies any involvement. Some experts point to the United States, which also speaks of its complete non-involvement in deaths.

Secrets of Nuclear Weapons

9. Mysterious drones over French nuclear power plants

In 2014, drones of unknown origin were spotted over 13 out of 19 nuclear power plants in France. The air areas over these territories are controlled by the French Air Force, but the aircraft were so small that they went unnoticed initially.
Despite the fact that the French government said there was no threat to power plants, the authorities spent one million euros to create systems for detecting and eliminating any such drones.

However, no one knows who launched these drones. Officials thought they had solved the case when they arrested three people who were preparing to launch a drone near a station in central France. But they had a simple, cheap version of the aircraft.
However, these people are now facing imprisonment and a fine of 75,000 euros.
Detected drones, as expected, cost at least several thousand euros each, and they could not be caught even with the help of coordinated efforts.
An army of helicopters was sent for one of the drones, however, the device turned out to be smart enough to escape from them.

Drones and their creators have raised concerns about the vulnerability of French nuclear facilities. Some point to Greenpeace , who previously used drones in their work, and who openly express their views on France’s nuclear program.
However, an organization is just one of several suspects because there is currently no direct evidence to support any of the theories.

Interesting facts about nuclear weapons

8. What is a ridge of fog?

When the U.S. Navy decided to tackle the restoration of its W76 warheads, which are a significant part of their nuclear arsenal, they faced a serious problem.
After opening the warheads, they discovered secret material, code-named "ridge of fog", which had to be replaced.
However, no one knew how to do this.

A ridge of fog was created in the 1970s and 1980s, and there were very few details about the process itself. Everyone who did this has not worked in this area for a long time. As a result, $ 23 million was spent on trying to create new material to no avail.
But after that, another 69 million was spent to resume the production process of the ridge of fog. Everything ended successfully.

Despite the fact that the ridge of fog is an important enough phenomenon in the navy to invest $ 92 million in taxpayers in the process, no one except the project participants knows exactly what it is.
Experts suspect that this is a kind of airgel that functions as a link in the warhead, helping the parts of the device to communicate with each other and transfer energy to each other.
However, whatever the ridge of fog is, it is a reminder that even the most important part of a technology can be a victim of time.
7. The Secret of Karen Silkwood

In 1974, 28-year-old Karen Silkwood was a laboratory assistant at the Kerr-McGee plutonium plant. It was believed that the plant had problems with quality control, as well as with safety procedures, and it was elected by the trade union committee to address the US Atomic Energy Commission with a status report.

With a folder of documents explaining the issues, Silkwood headed for a meeting with a New York Times journalist on November 13th. However, before reaching the meeting place, she turned off the road and crashed into a concrete wall. The woman died, but no documents were found
As a result of the investigation, the police found alcohol and sedatives in her blood, which led them to conclude that Karen fell asleep at the wheel.
However, the private investigator who studied the case found dents on the back of her car, and suggested that she might be forced to turn off the road.
An autopsy of the girl’s body showed that her body was suffering from severe radiation poisoning. A search of Karen’s apartment revealed that a huge amount of plutonium had accumulated in her kitchen, bathroom, and even on the sandwich in the refrigerator .

Plant lawyers suggested that the girl was emotionally unstable and depended on sedatives, as a result of which she was poisoned.
Nevertheless, regardless of whether Karen was a madwoman who poisoned herself or if she was killed by informants, the plant closed a year after the woman’s death , because the main company, which purchased fuel rods from him, began to complain about the poor quality of products and simply stopped buying them.
The Silkwood case has also been closed.
6. Nuclear alarm of 1969

In 1969, the Nixon administration secretly brought US nuclear forces on high alert without giving any reason. The reason was so highly classified that even the head of the Joint Staff Committee did not know anything.
Even today, no one can really explain why the administration then took such a potentially destabilizing step.
Declassified documents indicate a connection with the Vietnam War, implying that the administration decided to "play with muscles" to demonstrate its willingness to take any measures necessary to end the war.

This is consistent with Nixon’s “crazy theory”, which suggests that the president had a rather dubious approach to foreign affairs.
According to the theory, Nixon controlled in such a way as to look mad from the side so that the hostile communist countries of the bloc would not provoke him because of the fear of a nuclear response. Nuclear alarm looked like Nixon was preparing to attack North Vietnam with the goal of convincing Moscow to enter into negotiations with Hanoi.

According to other sources, the alarm was created in order to deter a Soviet nuclear attack on China during disputes over the Sino-Soviet border. Documents show that Soviet leaders were indeed considering a preemptive strike at Chinese nuclear facilities at that time.
Since even military leaders of the highest echelons were not "shining" then, Henry Kissinger is one of the few survivors who knows what happened. However, even he does not give any clear answers in his memoirs.
However, regardless of the true cause of this anxiety, it appears to have had little impact on external relations.