DESCRIPTION OF THE RADIATION MODULE OF MULTIPHYSICAL CODE FOR ANALYSIS OF THE BAFFLE GEOMETRY DEGRADATION

Abstract

To date, the possibility of lifetime extension for nuclear power units beyond the project period is extremely important, as well as developing new approaches to expand the previously estimated possible years of lifetime extension of power units, for which this period is almost exhausted. According to the design limit of safe operation for power units with VVER type of reactors - the limiting factor in terms of changes in the geometric state is the contact of baffle and peripheral fuel. Preliminary analysis of the geometric changes of reactor internals, which is mandatory during lifetime extension, showed that more expected is the contact of the baffle metal and barrel, which precedes the contact with nuclear fuel assemblies. An additional factor is that due to the design features of the baffle there are radial flows of coolant from the core to bypass. This situation is not foreseen by the project, so there are discussions in the domestic industry about further safe operation. The main reason for the change in geometry is the combination of accumulated radiation dose and the temperature field unevenness. The "classical" analysis, which is used for lifetime extension, consists of successive stages: the assessment of radiation conditions, temperature field calculation and, finally, the stress-strain state estimation. This approach is acceptable only in the case of a weak link between the physical modules (steps), and requires the conservative evaluation at each step. To date, this approach has almost exhausted itself, as the reserve of "guaranteed safe operation" years, which are estimated by the consistent approach, is almost expired. This paper describes the module for radiation loads estimation, which is a component of the multiphysical code for the analysis of baffle state in terms of its geometry degradation. This approach is developed by specialists of IPP-Centre LLC and PhD students and students of the university.