Influence of the Crosstalk Effect on the Correct Determination of the Affected SG During Prise Accident in VVER-1000

Abstract

The practical implementation of automated systems for management of primary-to-secondary leakage is a crucial issue for operational safety improvement at Ukrainian nuclear power plants. In this case, one of the main indicators of the primary-to-secondary leakage is the activity concentration increasing in the main steam lines of the affected steam generator. The detailed analysis of the geometrical features, arrangement of the main steam lines of the steam generator in VVER-1000 and radiation detectors allow identifying the crosstalk effect and its influence on the correct determination of the affected steam generator. The paper describes the main components of the developed models in the detection region in MCNP6.2 software. For the correctness of the comparative analysis, the distance between two adjacent main steam lines of the steam generators remains constant in all models. The radiation detectors have been modelled in the regular location and adjacent to the main steam lines of the steam generator. The registration efficiencies of ionizing radiation from 16N by the sensitive elements of the detectors such as BDMG-04-02, SGLM-201-1 and GIM-204 have been assessed. BDMG-04-02, SGLM-201-1 and GIM-204 responses, depending on the activity concentration of 16N in the detection area and considering the nonproportionality features of the devices, have been estimated. The presence of crosstalk effects has been confirmed. The significant influence of the paralyzing and non-paralyzing dead time on the reliable determination of the activity concentration and correct identification of the affected steam generator have been emphasized. The obtained results can be used as initial data for justification of system setpoints for launching the automated algorithm to manage the primary-to-secondary leakage accident without operator’ actions and fulfill its improvement.