Numerical investigations of protective shells of NPP evergy units with pressurized water reactor (VVER)

Abstract

Most of the energy units of nuclear power plants in Ukraine are at the stage of exhausting their design lifespan. Therefore, the issue of extending the lifespan of energy units of nuclear power plants (NPP) and, consequently, assessing the residual life of protective shells is very acute. State Enterprise "The State Research Institute of Building Constructions" developed universal computer models of NPP energy units from VVER-1000 type V-302 and V-338, taking into account all the design features of protective shells, load connections and the possibility of varying the level of pre-tensioning of ropes. The developed models made it possible to evaluate the operability of a localizing safety system - a hermetic enclosure system in all operating modes, including a combination of loads during a design basis accident and a maximum design earthquake. The purpose of this work is: on the basis of numerous studies of the load-bearing capacity of the protective shells of energy units in all operating modes, to develop a methodology for determining the rational tension of the ropes in rows, at which the forces in the ropes of all three rows under the action of emergency load coupling during normal operation plus design basis accident plus the maximum design earthquake (NO + DBA + MDE) is distributed most evenly and, as a result, the probability of breaking the ropes of the outer row during an accident is reduced.
 As a result of numerous studies of the load-bearing capacity of the protective shells of energy units in all modes of operation and the determination of the rational tension of the ropes in rows under the action of NO+DBA+MDE, the following has been established: minimum allowable tensile force of reinforcing ropes in the cylindrical part of the protective shell of the energy unit in the absence of two ropes; minimum allowable tensile force of reinforcing ropes in the cylindrical part of the protective shell of the energy unit in the absence of three ropes. The rational distribution of rope tension between the rows is determined, in which the efforts in the reinforcing ropes of all three rows under the action of NO+DBA+MDE are distributed most evenly and, as a result, the probability of breaking the ropes of the outer row in case of an accident is reduced.