Ukraine has sentenced three officials at the Chernobyl nuclear power station to five years in prison for stealing radioactive pipes worth around $125,000, the country's security service said on Thursday.

Three officials working at the now defunct Chernobyl Atomic Power Station, site of the world's worst nuclear disaster, had stolen 24 tonnes worth of pipes made of copper nickel alloy, the SBU security service said in a statement.

Worth more than 1 million Ukrainian hryvnias ($125,000), the pipes had been stolen from the territory of a sarcophagus around the reactor that exploded on April 26, 1986 contaminating large parts of Europe but especially the then-Soviet republics of Ukraine, Belarus and Russia.

Authorities began a criminal case into the theft last year and investigators established the officials had taken the radioactive pipes from the territory of the plant using forged documents, the SBU security service said.

"The radio-contaminated pipes have been returned to a special storage facility for nuclear waste," the security service said. The officials have been sentenced to five years in prison, it added.

The identity and position of the officials were not disclosed.

Thousands of workers still tend to the now defunct power station to make sure contamination does not spread beyond the exlusion zone.

The Ukrainian authorities are now raising money to complete a permanent shelter to secure the ruins of the exploded power station.