On 14th July 2015 Iran signed the nuclear agreement with five permanent members of the United Nations Security Council, U.S.A, Britain, France, Russia, and China plus Germany, which is known as Joint Comprehensive Plan of Action (JCPOA).
According to that deal, after signing the agreement Iran cannot store more than 130 tons of heavy water during the first year and should sell any excess supply of both heavy water and enriched uranium in the international market. Under the deal Iran is allowed to use heavy water in its modified Arak nuclear reactor. In April 2016 Russia’s foreign ministry announced that Russia was considering purchasing 40 tons of heavy water from Iran.
According to Mr. Sergey Kirienko (former head of Rosatom and actual deputy chief of staff in charge of domestic politics), 38 tons of Iran heavy water was delivered to Russia in two flights on September 13 and September 20 as a part of deal between Russia and Iran.