In 2019, Russia and China signed a contract for the supply of HEU fuel for the first seven years of operation of the CFR-600 fast neutron reactor. The reactor, located at Xiapu, started operations in December 2023. The second reactor, which is under construction at the same site, is expected to begin operations in 2026.
Fast neutron reactors can produce high-quality weapon-grade plutonium in the uranium blanket surrounding the active zone. China has maintained that this material will be used exclusively in its peaceful program. And indeed, the terms of the fuel supply agreement appear to restrict the use of the plutonium produced when the reactor uses the HEU fuel supplied by Russia.
Two key documents that regulate the issue are the Russian Regulations on the Export and Import of Nuclear Materials, first issued by the Russian government in 2000 and last amended in February 2023, and the Agreement on Cooperation in the Area of Peaceful Use of Nuclear Energy, which Russia and China signed in 1996.
According to paragraph 6 of the Regulations, export of materials like HEU to nuclear weapon states is allowed only if
exported items and items produced based on them will not be used for the production of nuclear weapons and other nuclear explosive devices or for any military purposes.
The Regulations requires the recipient state to provide written guarantees of peaceful use, which is then assessed by Rosatom (paragraph 8).
Article 4 of the Agreement on Cooperation contains similar language:
The parties assume that the items of nuclear export transferred under this Agreement will not be used for the production of nuclear weapons and other nuclear explosive devices or for any military purposes.
These two documents clearly prohibit the use "for any military purpose" of the plutonium that would be produced by any reactor that uses HEU fuel supplied by Russia.
UPDATE: The agreement on cooperation regarding CFR-600 specifies that Russia will provide MOX fuel or MOX fuel fabrication technology as well, further prohibiting the military use of plutonium produced by the CFR-600 reactors.