Russian armored vehicles streaked past a nuclear reactor and high-tension electrical lines in the dark. There was a fire. The reactor containment vessel was sprayed with shrapnel.

Operators were horrified in the control room of the reactor.

One begged to stop firing at the facility. You are putting the safety of the world at risk.

The Zaporizhzhia Nuclear Power Plant's sprawl of cooling towers, nuclear reactor, machine rooms and radioactive waste storage sites was graver than those who worked there knew.

A large caliber bullet had pierced an outer wall of Reactor No. 4 but, most worrying and not disclosed at the time, an artillery shell had struck an electrical transformer at Reactor No. Both of the reactor were running.

Standing between the world and a nuclear calamity are the Ukrainian workers who have run the plant for years in a sleepy corner of southern Ukraine where the city and the plant had once lived in a steady and predictable relationship.

ImageRussian soldiers in front of the Zaporizhzhia Nuclear Power Plant in May.
Russian soldiers in front of the Zaporizhzhia Nuclear Power Plant in May.Credit...Sergei Ilnitsky/EPA, via Shutterstock

Under Russian occupation, the plant employees are both hostages and essential workers, with Ukrainian engineers duty bound to prevent disaster while working under the watch of Russian snipers.

The city where they live is under attack. Russian forces have been accused of detaining some 100 plant workers. Ten of them are not found.

It is up to a group of stressed, tired and scared workers.

Serhiy Shvets, a metalworker who was shot by Russian soldiers at his home in May, said that men and women coming to work would face armed soldiers all around. They looked at videos of people who protested in the first days of the war.

Mr. Shvets was able to leave the city and speak from his hospital bed. He is worried about the plant, the city and the world now that the Russian military is in the nuclear station.

He said that they are like a monkey with a grenade.

The Day of the Energy Engineer was celebrated by the community in the shadow of Europe's largest nuclear power plant.

There were a lot of things to do. Olha, an engineer who attended the celebrations and fled the city in May, said it was cool.

Olha spoke only on the condition of anonymity because she was afraid for her safety.

Olha, an engineer at the plant, said its employees “are literally working at gunpoint.”Credit...Lynsey Addario for The New York Times

Ten thousand people worked at the plant in the city. The flag of the city has a blazing sun in it.

The work on Zaporizhzhia started in 1984. Four years after the fall of the Soviet Union, Ukrainians celebrated Zaporizhzhia as an accomplishment.

It became both a source of pride and a symbol of Ukrainian perseverance after the 1986 Chernobyl nuclear disaster when a safety test simulating the effects of a power failure ended in what many considered to be the world's worst nuclear disaster.

After Chernobyl, the authorities issued a brief moratorium on nuclear construction, but it was not long before the country began to build nukes. France is the only country that uses its reactor network to meet its electricity needs.

The Zaporizhzhia site has unique vulnerabilities.

Much of the plant's inner workings are exposed and it is vulnerable to the conflict now raging around it.

On a recent summer afternoon, the cooling towers, smokestacks and containment vessels could be seen from the opposite shore of the Kakhovka dam.

A satellite image showing the six reactors at Zaporizhzhia.Credit...Maxar Technologies, via Associated Press

In 1999 Zaporizhzhia established its own radioactive waste storage system in order to end dependence on Russian reprocessing.

What we consider before using anonymous sources. How do the sources know the information? What’s their motivation for telling us? Have they proved reliable in the past? Can we corroborate the information? Even with these questions satisfied, The Times uses anonymous sources as a last resort. The reporter and at least one editor know the identity of the source.

Today's storage site is an especially dangerous one.

Nuclear power plants are meant to abide by seven pillars of safety, which include ensuring the plant's physical integrity, keeping safety systems fully functional, maintaining a staff free of pressure, and monitoring on-site and off-site radiation.

The International Atomic Energy Agency says that nearly all the principles are being violated.

The main condition for operating a nuclear plant is calm, according to a human resources executive who worked in the plant. He said that it should be calm. Everything calms at home for an employee. A person who is calm is more likely to make better decisions. A person making mistakes in a state of fear.

Mr. Gortenko rose from being an engineer to overseeing the licensing of reactor operators. He liked working at the plant because it was a family affair. His father and mother were both librarians, the same position his wife was in.

The city and plant worked well together. Safety drills were held at the plant for those living and working nearby.

Mr. Gortenko and other employees wore uniforms that were white for scientists, gray for supervisors, blue or black for others when they traveled to work. The workers ate at the cafeteria.

About 600 employees were required for each reactor and machine room complex. They worked in three eight-hour shifts that alternated from morning to evening to night.

Employees worked on electricity networks near the Zaporizhzhia plant on Monday.Credit...Alexander Ermochenko/Reuters

He said that the culture was attentive to detail. Minor accidents were recorded.

The plant was kept free of all disruptions.

The situation at the plant is not an emergency they had anticipated.

The Russians invaded the plant that night. Half the windows in his building were shattered when the shooting ended.

There was a cold wind blowing through the offices.

The workers resumed their work after taping plastic over the broken panes. Russian soldiers showed up from time to time. He didn't think they were threatening workers, but they were armed.

According to messages shared with The Times, the employees were entering the plant under Russian guard by the spring.

The engineer was sent a message saying that Russians were on the roofs of the buildings. Employees are working at gun point.

A Western official and witnesses say 500 Russian soldiers are at the plant. The senior Western official who has a reputation for brutality said they are believed to be members of the Rosgvardya.

The Russian soldiers tore down the town's flag and replaced it with a Russian tricolor and a hammer and sickle of the former Soviet Union.

Ukrainian emergency rescue teams practiced a nuclear disaster drill in Zaporizhzhia this month.Credit...David Guttenfelder for The New York Times

People living in the area say the Russians have been drinking, raiding and detaining people for expressing a hint of protest. People in the close-knit company town shut themselves indoors as their friends went missing.

In one case, a person was taken into the forest and shot at in a mock execution. There was a list of people.

There is no information about a man who went missing in March. A man was taken to the commandant's office and killed.

She said that the Russians called his mother and told her to collect his body after he was killed.

There is a swirl of violence in the town because of the oppression and resistance to the Russians. The Russians installed a new mayor, Andrii Shevchyk, after he was injured in a bombing.

Russian soldiers shot and killed Mr. Shvets at the front door. Mr. Shvets said he had no connection to any organized insurgency but he did staff the barricades as Russians approached the city.

Fearing for their families, employees at the nuclear plant showed up for work in the reactor control rooms, pumping stations and turbine compartment.

As the Russians tightened their grip on the plant and the city, officials at the Ukrainian company that oversees the nation's 15 nuclear reactor decided to allow some non essential staff to leave.

As fighting raged around the nuclear plant, a Ukrainian family joined a convoy of civilians fleeing the area.Credit...David Guttenfelder for The New York Times

The company decided to distribute its entire stock of the drug in April.

About 400,000 people living in Ukrainian-controlled territory are likely to be in the radiation fallout zone if there is a meltdown.

The plant has been hit with shells. Employees say that explosions are heard a lot.

On Monday, Ukrainian officials said that there had been shelling again near the plant and that a man had been killed and several others injured when Russian soldiers opened fire on their car.

The peaceful functioning of the plant depends on the people who live there.

Many of the people who are still working would like to leave.

A housing and care center in Zaporizhzhia for those evacuated from the Russian-occupied area.Credit...David Guttenfelder for The New York Times

There are two people reporting from Zaporizhzhia and Kyiv. Anna Lukinova reported from Kyiv.