Chernobyl's power plant managers 'hid' their radiation levels so they could protect cleanup workers, said former deputy director

• Chernobyl was one of the worst nuclear disasters the world has ever seen, resulting in widespread contamination throughout Europe.
• Workers on the cleanup site immediately following the accident had to record their radiation levels using a dosimeter, or device that measures a person's dose of radiation.
• The former deputy director of the Chernobyl Nuclear Power Plant, Alexander Kovalenko, said management officials used to hide their dosimeters in less contaminated areas so they would be permitted to stay on the job site.
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In July 1986, Alexander Kovalenko was called to assist with the cleanup of one of the world's worst nuclear disasters. Three months earlier, the core of a reactor had opened at the Chernobyl Nuclear Power Plant, sending plumes of radioactive material coursing through the air.

As the plant's newly-appointed deputy director, Kovalenko's job was to ensure workers' safety.

Read more: The former deputy director of the Chernobyl Nuclear Power Plant says the HBO series got its villain right, but its hero wrong

By day, he worked tirelessly to protect staffers from radiation released by a steam explosion and subsequent fires. At night, he slept for about three to four hours in an abandoned mental institution. His roommate was Chernobyl's chief scientific investigator, Valery Legasov - now the protagonist of a new miniseries on HBO.

The job was so high-stakes, Kovalenko said, that management officials found ways to under-report their levels of radiation in order remain on the job site.

"I was amazed at people's behavior," he said. "No one was waiting for [an] order. ... People worked not from fear, but from conscience. No one thought about punishment or rewards and money."

Kovalenko's assignment involved exposing himself to radiation, but there were rules to protect his safety.

Each cleanup worker was given a dosimeter to record their levels of radiation exposure. Every other day, staffers had to present their dosimeter to a monitoring service for inspection, he said. Workers that accumulated radiation above a certain threshold (about 25 roentgens) were asked to leave the contaminated area - what Kovalenko called the "dirty zone."

That was a problem, said Kovalenko, since it meant constantly training new specialists, who were hard to come by.

Kovalenko said specialists had to be capable of operating a nuclear reactor and familiar with the aisles, corridors, and galleries of a nuclear power plant. If the cleanup wasn't successful, he said, the Soviet Union might have stopped operating all of its RBMK reactors (the kind used at the Chernobyl plant).

His personal mission became twofold: to prevent staffers from becoming "burned," or irradiated, and to stick around long enough to finish the cleanup. Because of that, he said, managers at the plant were willing to incur higher levels of radiation to protect their staff.

"We did not want to quit what we started," he said. "I, like almost everyone in management, hid the dosimeter in the 'clean zone,' [an area outside the power plant determined to have safe levels of radiation]." This ensured that Kovalenko's dosimeter showed lower doses of radiation than he was actually receiving.

The trick allowed him to continue working in the contaminated area for about five months, until he was eventually caught by monitors who traced his route.

"It became clear that the dose of radiation I adopted was significantly higher," he said. On New Year's Eve 1986, he was withdrawn from the contaminated zone - but his stay in Chernobyl wasn't over.

By that time, Kovalenko had become professionally acquainted with Boris Shcherbina, the chairman of the Chernobyl commission (whose character also appears in the HBO series).

"He was a very strict boss," Kovalenko said. "In Chernobyl, only four people were not afraid of him ... but everyone respected him without exception."

Kovalenko said Shcherbina took pity on him and offered him a job as public relations chief in 1987. In his new role, Kovalenko wound up presenting AZ-5, the infamous emergency response button that set off the explosion, to visitors.

"There were no particular emotions," he said. "If you are a professional and understand what you are doing, everything is OK."

As for the long-term effects of radiation exposure, Kovalenko said working at the Chernobyl cleanup site wasn't a death sentence.

"Radiation has a different effect on everyone," he said. "I know many professionals - scientists, engineers, military personnel - who [acquired high doses] and lived to a very old age."

Kovalenko is now 66 years old and lives in Norway. In 2005, he wrote an open letter criticizing the Russian government's treatment of Chernobyl survivors. Two year later, he said, he was forced to leave the country.

Read more Chernobyl coverage:

Real-life characters in HBO's 'Chernobyl' on the moment they found out about the disaster

HBO's 'Chernobyl' series invented a main character

Russia still has 10 Chernobyl-style reactors that scientists say aren't necessarily safe