The 70 raids followed a 15-month investigation into the sector. Nabu said it had uncovered a "high-level criminal organisation" in which bribes were linked to contracts awarded by nuclear power company Energoatom.
Around $100 million has passed through the money laundering system used, according to Nabu.
As recently as last summer, President Volodymyr Zelensky's government planned to limit the independence of Nabucco and the Specialized Anti-Corruption Prosecutor's Office (Sapo). However, after widespread protests, the government was eventually forced to back down.
In his evening speech on Monday, Zelenskyy says that anti-corruption efforts are necessary.
Transparency in the company (Energoatom) is a priority, says the president.
Judgments must be issued and state representatives must cooperate with Nabu, and with law enforcement agencies.
Energoatom confirms that the raids have been carried out and states that it is cooperating with investigators, but does not comment on the specific allegations.
The Ukrainian energy sector is also being hit hard by the recurring Russian attacks, and is preparing for another winter of war.
