By 2030, the construction will begin of an innovative pressurised water reactor with spectral control – the VVER-S, Russian Deputy Prime Minister Alexander Novak said in a presentation concerning the federal project on New Nuclear Energy.
"Design documentation has been developed, a licence has been obtained for the construction of a water-cooled power reactor with spectral regulation," according to the presentation.
The VVER-S is being developed by Rosatom’s OKB Gidropress. The fundamental difference between the VVER-S and conventional VVERs lies in spectral regulation — the replacement of liquid boron regulation and reactor control by changing the water-uranium ratio in the core. This is done through the introduction of displacers into and out of the core during the fuel campaign. In VVER-S, instead of absorption in boric acid, excess neutrons are absorbed on uranium-238. This produces plutonium - a new fissile fuel.
Gidropress says the use of a spectral regulation system has a number of advantages. It saves natural uranium - at the same power, a spectrally controlled reactor will consume 30% less uranium in an open fuel cycle. However, the VVER-S can operate in both an open and closed fuel cycle. Spectral control makes it possible to load into a light water reactor a core consisting entirely of mixed oxide (mox) fuel. Currently, light water reactors can be loaded with a core containing no more than 50% mox. Thus the VVER-S can consume regenerated fuel within the framework of a closed nuclear fuel cycle. In addition, the required level of safety for generation 3+ nulcear power plants is ensured without the need for a boron regulation system. The design service life of the main equipment is at least 60 years.
Initial work on the VVER-S began in 2019 with the aim of developing the main design solutions related to core physics, technological systems and design optimisation.
The use of displaces makes it possible to create a harder neutron spectrum at the beginning of the fuel campaign and to use the neutrons that are normally absorbed in conventional VVERs to produce new fissile materials. As the core burns out, the displacers are removed and replaced by water. At the end of the fuel campaign, VVER-S will operate like a conventional VVER.
The main parameters in the reactor are approximately the same as in the VVER-TOI project, and the materials for the VVER-S will be the same. The only change that might be needed is for the internals. For these, new steel is being developed at the Prometheus Central Research Institute of Structural Materials. The service life of internals made of new steel will be longer.