According to Ukrinform, the UK Defense Ministry announced this on X (formerly Twitter) with reference to intelligence data.
According to the tweet, on September 10, 2023, Energoatom, Ukraine's nuclear power plant operator, announced it had successfully refueled a reactor at its Rivne Nuclear Power Plant (NPP) using Western-produced nuclear fuel assemblies.
All of Ukraine's NPPs have reactors based on Soviet designs and until February 2022 it relied on Russia for nuclear fuel. Since Russia's full-scale invasion, Ukraine has accelerated plans to diversify its supply.
"With nuclear energy supplying approximately half of Ukraine's electricity, Energoatom's success in sourcing and installing Western fuel is a major waypoint in Ukraine's long-term decoupling from Russia whose influence over Ukraine's energy supply is severely diminished," the ministry said.