The secondary circuit of Iran's Arak heavy water nuclear reactor will become operational on Monday, the country's semi-official Mehr news agency reported.
The starting of the secondary circuit will not violate restrictions placed on Iran's nuclear program under a 2015 deal with world powers, but shows Iran is continuing work to develop the reactor amid renewed tensions with the United States.
As part of the deal, the core of the Arak reactor was removed and filled with concrete to make it unusable, but Iran was able to continue to produce heavy water.
"The first circuit is tasked with removing heat from the heart of the reactor, and the secondary circuit is responsible for transferring the heat from the first circuit to cooling towers and finally to the outside environment," Mehr reported.