Benchmarking the Real-Time Core Model for VVER-1000 Simulator Application on Asymmetric Core Load

The aim of this paper is to summarize authors' experience in adaptation of an existing plant-specific VVER-1000/V320 model for simulation of a rare example of a Kalinin 3 nuclear power plant (NPP) transient of “switching-off of one of the four operating main circulation pumps at nominal reactor power” with an asymmetric core configuration. The fidelity and accuracy of simulation with emphasis on reactor core model is illustrated through comparison with plant-specific data. Simulation results concerning fuel assembly (FA) power and axial power distribution during the transient are compared with records from Kalinin 3 in-core monitoring system (ICMS). Main operating parameters of nuclear steam supply system of a VVER-1000/V320 series units vary to a considerable degree. While Kalinin 3 benchmark specification contains very good description of the transient, as well as record of many parameters of the unit, the document provides only superficial description of the reference unit. In such a case, an approach based on a “generic” V320 model by default introduces deviations which are difficult to quantify. There are several examples which warrant discussion. Some of the most important lessons learned are as follows. (1) individual characteristics of all the main circulation pumps and the reactor coolant loops are quite important for the quality of simulation and should be accounted for in the model; (2) variations in fuel assembly characteristics should be accounted for not only in terms of macroscopic cross section library but also in terms of local pressure loss coefficients and mixing factors in the case of mixed core loads; (3) comprehensive plant-specific model of dynamic response of instrumentation and control (I&C) systems is a necessity; dynamic characteristics of individual measurement channels (nuclear instrumentation, pressure, temperature) should be accounted for; and (4) comprehensive plant-specific model of balance-of-plant equipment, instrumentation, and control is a necessity. Above requirements impose a difficult task to comply with. Nevertheless, any individual nuclear power unit is supposed to maintain a detailed design database and data requirements for plant-specific model development should be considered.