Russian state nuclear company Rosatom has suspended work on modernizing a unit of Iran's Fordow nuclear complex due to an issue with uranium compatibility, Rosatom's nuclear fuel cycle unit TVEL said on December 5.
"Uranium enrichment and the production of stable isotopes cannot be carried out in the same room," TVEL said in a statement, adding that the implementation of the project was "technologically impossible" currently.
TVEL said its experts have been working since 2017 on a project to modify centrifuge cascades to produce two stable isotopes that can be used for medicinal purposes.
But it said their efforts have been rendered useless by traces of uranium in the air and on the equipment.
"To resume this work, we must stop and dismantle the cascades, where uranium enrichment takes place, and thoroughly clean the premises and equipment," said TVEL. "Until these conditions are met, works on the project from the Russian side are suspended."
The United States last month said it would cease waiving punitive sanctions related to the Fordow plant from December 15 after Tehran resumed uranium enrichment at the underground site in breach of a nuclear accord it signed with world powers in 2015.
After President Donald Trump last year announced that the United States was withdrawing from the deal under which Tehran pledged to restrain its enrichment program, European countries have tried to salvage the landmark nonproliferation agreement.
But Iran has increasingly distanced itself from the accord after Washington's decision.