Russia’s AI Leipunsky Institute of Physics & Power (IPPE, part of Rosatom’s Scientific Division) has begun tests to substantiate the neutron physics characteristics of the core of a VVER-S spectral-controlled reactor.
The VVER-S is a promising light water reactor for power units with a capacity of 600 MWe. The fundamental difference is the spectral regulation of changes in the reactivity reserve of the core during fuel burn-up. This is due to changes in the water-fuel ratio when the reactor is operating at capacity.
Also involved in the tests are Rosatom fuel company TVEL and enterprises of the Rosatom’s Fuel Division – the Siberian Chemical Combine (SSC) , Mashinostroitelny Zavod (MSZ – Machine-Building Plant and the Kurchatov Institute. These participated in various stages of the work including preparation for the experimental studies., development of design documentation, and manufacture of various elements for subsequent experiment, including fuel rods, absorbing elements (PEL – Pogloshayoshie Elementi), various simulators, displacers, etc.
Fuel rods with mixed oxide (MOX) fuel from energy-grade plutonium for experimental research were manufactured at SSC in Seversk and supplied to IPPE. To carry out neutron physics research, changes were made to the design and operational documentation of the BFS-1 critical nuclear stand.
“In anticipation of the physical launch, a mock-up of a critical assembly without nuclear materials inside was fully formed and submitted to the Nuclear Safety Commission, which checked the readiness of all critical stand systems and personnel, the physical launch control programme, and authorised the physical launch control. After receiving permission, the models were portioned out and replaced with real fuel rods containing plutonium,” said Alexander Zhukov, head of the BFS complex.
At the BFS-1 critical stand, large-scale experimental studies of the neutron-physical parameters of the VVER-S reactor core with spectral regulation were initiated by IPPE specialists in 2023. This reactor plant is a development of the VVER reactor, but with the use of MOX fuel and an additional system for spectral regulation of the fission reaction in the core. The work was carried out in several stages. The first stage in 2023-2024 was a critical assembly, assembled in the classic tube-block version for the BFS complex. At the second stage, starting in 2025, after changes were made to the terms of the licence for the operation of the BFS-1 critical stand, a central insert (tank) filled with water and VVER-S fuel rods with MOX fuel was installed.
The VVER-S reactor installation is the result of the consistent development of VVER technologies and is aimed at improving its technical and economic parameters. The first such reactor installations are planned to be built at the Kola-II NPP in the Murmansk region. One of the innovations is the ability to spectrally control the fission reaction instead of using boric acid. With this method of regulation, excess neutrons will be absorbed by U238 nuclei and lead to the formation of PU239, which in turn will extend the fuel campaign, increase the capacity utilisation factor and improve the economic characteristics of the reactor. The study of the neutron-physical characteristics of operating VVER reactors with MOX fuel will make it possible to take another step towards creating a two-component nuclear energy with VVER and BN reactors.
Based on the results of the research, Rosatom scientists intend to substantiate the neutron-physical characteristics and safety of operation in various modes of VVER reactor installations with MOX fuel (including future promising installations.
The BFS rapid physics test facility, which includes two critical test facilities, BFS-1 and BFS-2, provides a unique experimental base for studying physics, primarily of fast reactors, solving safety problems, optimising active zones, and substantiating the parameters of a closed fuel cycle. More than 150 critical assemblies have been assembled and examined at critical stands. The successful operation of BFS-1 and BFS-2 for more than half a century required their technical re-equipment, which was carried out within the framework of the Federal Target Programme for Nuclear Energy for 2012-2016.
