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.
Highlights
On December 31, 2009, after the final shut-down of Unit 2 (Unit 1 was closed down on December 31, 2004), the Ignalina Nuclear Power Plant (INPP) terminated generation of electricity
CPSCC-37 is the inner surface of the heat exchanger pipes, it is washed by non-contaminated water
After 35 years, contamination of the CPSCC components is highly determined by a long-lived nuclide Ni-63 since short-lived nuclides decay in a short time (Fe-55, Co-60, Mn-54, Fe-59)
Summary
On December 31, 2009, after the final shut-down of Unit 2 (Unit 1 was closed down on December 31, 2004), the Ignalina Nuclear Power Plant (INPP) terminated generation of electricity. Contamination of the systems’ components with radioactive particles is a result of the contaminated cooling water circulating within these systems during operation of the reactor. The corrosion products of the systems’ components are transferred by the coolant to the reactor active zone. They form deposits on the surfaces of the equipment and are activated by high neutron fluxes. Due to erosion, these activated particles pass to the coolant and, due to its circulation, are deposited on the surfaces of the equipment located outside the reactor active zone. In order to facilitate determination of the circulation pumps’ radioactive contamination, a conservative assumption was made presuming that two of the pumps work all the time during INPP operational time and the contamination of the remaining items is the same
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