Three innovative fuel cassettes have been loaded into the VVER-1000 reactor at unit 1 of Russia’s Balakovo NPP. Each contains 312 chromium-coated fuel elements over a classic zirconium alloy, 18 of which contain uranium-plutonium mixed oxide (mox) fuel.
The chosen combination of these fuel and structural materials is important for solving the strategic task of involving both fast reactors and classical thermal light water reactors in a closed fuel cycle. Mox technology allows the use of secondary materials from nuclear reprocessing – depleted uranium and plutonium extracted from used nuclear fuel for the production of fresh fuel.
Chromium-plated fuel element cladding, originally developed for accident tolerant fuel, not only improves core stability and safety in the event of severe post-design accidents but due to their surface properties make it possible to move to fully automated fabrication of fuel assemblies avoiding fuel manufacture operations that currently require manual labour. To minimise the radiation impact on production personnel, the industrial fabrication of uranium-plutonium fuel needs to be fully automated.
Rosatom’s first uranium-plutonium fuel for VVER reactors was REMIX fuel – its pilot operation was successfully completed at the Balakovo in March. The plutonium content in the new mox fuel is several times higher than in REMIX fuel. It also contains depleted uranium rather than enriched uranium. This will make it possible to optimise the economics of fuel fabrication, use regenerated nuclear materials more flexibly, and also utilise the reserves of accumulated depleted uranium.
Rosatom specialists calculate that, if the VVER fuel assembly is equipped with 25% fuel rods based on mox fuel, and the remaining 75% with standard fuel rods with enriched uranium (including regenerated material), then the overall plutonium content will be equivalent to REMIX-assemblies
The working name for a similar hybrid fuel assembly with a mixed fuel type is heterogeneous REMIX. Calculations by specialists from Rosatom’s Fuel Division TVEL for power units with VVER-1200 reactors show that the introduction of heterogeneous REMIX fuel will reduce the consumption of natural uranium during the NPP life cycle by more than 20%.
The strategic goal of Rosatom and our image for the future is a two-component nuclear power system in which fast and thermal reactors operate in a closed fuel cycle, and the used fuel of some installations becomes the raw material for fresh fuel for other reactors,” said Alexander Ugryumov, Senior Vice President for Research Activities at TVEL. “Everything we do in scientific and technological projects on fuel for the VVER is devoted mainly to this goal.”
He added: “Today we are already undergoing trial operation of both the design of the fifth-generation fuel assembly for the VVER-1200, and fuel rods with mox fuel and chrome cladding. There is even a project for a new technology for manufacturing fuel pellets for automated fabrication. In the future, we plan to combine all these new solutions for materials, structures and fabrication technologies in one product.”
Vladimir Dergachev, head of the nuclear safety and reliability department at the Balakovo NPP noted: “The trial operation of mox fuel at the Balakovo NPP is being carried out in strict coordination with Rostechnadzor and in accordance with the licence issued by the regulator.”
Before loading the innovative fuel into the VVER-1000 core, Rosatom tested the mox fuel rods at the enterprises of its Scientific Division – in a reactor at the Scientific Research Institute of Atomic Reactors (NIIAR – Nauchno Issledovatelskii Institut Atomnikh Reaktorov) in Dimitrovgrad as well as at the BFS-1 critical stand at the AI Leipunsky Institute of Physics & Power Engineering (IPPE) in Obninsk.
The manufacture of the innovative fuel cassettes involved broad industry cooperation, including the Mining & Chemical Combine (GKhK – Gorno Khimicheskii Kombinat), in Zheleznogorsk, as well various TVEL enterprises including the Chepetsky Mechanical Plant (ChMZ – Chepetskii Mekhanicheskii Zavod) in Glazov, the Machine Building Plant (MSZ – Mashinostroitelny Zavod) in Elektrostal, the Novosibirsk Chemical Concentrates Plant (NZKhK – Novosibirskii Zavod KhimConsentratov) and the Siberian Chemical Combine (SKhK – Sibirskovo Khimicheskovo Kombinata) in Seversk.
