Modelling of the Radiological Contamination of the RBMK-1500 Reactor Control and Protection System Channels’ Cooling Circuit

Abstract

The article presents results of modelling and analysis of component contamination of the RBMK-1500 reactor Control and Protection System channels' Cooling Circuit (CPSCC) at Ignalina NPP Unit 1. The modelling was performed using a computer code LLWAA-DECOM (Tractebel Energy Engineering, Belgium), taking into consideration CPSCC components characteristics, parameters of the water flowing in the circuits, system work regimes, etc. During the modelling, results on activity of CPSCC components' deposits, nuclide composition of the deposits and dose rates after the final shutdown of the reactor, as well as activity decay of the most contaminated CPSCC components' deposits were obtained. Analysis showed that there is a significant difference in contamination levels between CPSCC components. The rundown header from the channels of the reactor's fast acting scram system is the most contaminated component, and contamination of the least contaminated component is only 0.27% compared to the activity of the most contaminated component. Corrosion nuclides are the nuclides that mostly contribute to contamination of the CPSCC deposits.

Assessment of the Radioactive Contamination of the RBMK-1500 Reactor’s Steam Pipelines and High Pressure Rings

“…At the final shutdown of the reactor, radiation from the deposits on SP-HPR components is mostly determined by Mn-54, Co-58, Fe-59, and Co-60. But due to longer half-life, Co-60 is the most significant contributor to the total dose rate five years after [14], PCS [15], LSWS [16], and CPSCC [17] subsystems components compared to the MCC MCP activity (PCS-i:LSWS-i:CPSCC-i:SP-HPR-i / MCC pump).…”

“…The scattering in the deposit activity ratio (at the final shutdown of the rector) between the most (the top of the bar) and the least (the bottom of the bar) contaminated components of the SP-HPR, MCC [14], PCS [15], LSWS [16], and CPSCC [17] systems compared to the activity of the MCC characteristic component (main circulation pump, MCP) is presented in Figure 5. As is shown in the chart, the activity of SP-HPR is lower than that of MCC and PCS nonpurified water subsystem.…”

“…Figure 5: Comparison of relative deposit activity of SP-HPR, MCC[14], PCS[15], LSWS[16], and CPSCC[17] subsystems components compared to the MCC MCP activity (PCS-i:LSWS-i:CPSCC-i:SP-HPR-i / MCC pump).…”