РАСЧЁТ ПО ПРОГРАММАМ MCU-PD И ТВС-М ПОКАЗАНИЙ ДЕТЕКТОРОВ ПРЯМОЙ ЗАРЯДКИ

Abstract

For successful licensing and safe passage of pilot operation of a new type of fuel in the core of an operating VVER-1000 reactor, it is necessary to carry out a preliminary validation of design codes that are routinely used for developing fuel cycles, core safety analysis and calculating maintenance of power unit operation. Validation matrix of the design codes includes problems of calculating transition functions of self-powered neutron detector (SPND). SPNDs are the part of incore monitoring system, which allows to determine power density in the core of an operating power unit. Transition functions from the self-powered detector current to the power density are calculated by means of TVS-M spectrum code. For each type of FA and each instance of self-powered detectors, transition functions are calculated in advance. Transition functions are never corrected during operation, therefore, strict requirements are imposed to the accuracy of their calculation. The main objective of the work is a comparative analysis of the TVS-M spectrum code and the MCU-PD Monte Carlo code as applied to the calculation of transition functions of self-powered neutron detectors for VVER fuel assemblies. During the work, we created calculation models of several types of fuel assemblies, differ in type of fuel, presence of fuel rods with Gd, and placement of SPND. We performed several series of calculations of the created FAs at different burnup steps. The calculations were carried out in states with different coolant parameters, fuel temperatures and presence of control rods. As the target functionals, we considered SPND current, SPND transition function and power density factor of six fuel rods surrounding SPND. We determined maximum relative deviations of TVS-M from MCU-PD in the target functionals calculation. We confirmed acceptable accuracy of calculations of the target functionals by means of TVS-M code for wide range of reactor parameters. We also estimated the influence of homogenization of the SPND structure on the accuracy of transition function calculation.