Thermal-hydraulic calculations for technical condition and lifetime extension assessment of SUNPP-3 reactor

Abstract

This paper presents the results of thermal-hydraulic calculations performed as part of the technical condition and lifetime extension assessment of SUNPP-3 reactor. Based on the recommendations of the IAEA and the results of previously performed computational analyzes, the main conservative assumptions for the analysis of the selected computational scenarios were identified. These assumptions, in the form of initial and boundary conditions, were used in thermal-hydraulic analysis analyzes. When choosing the initial and boundary conditions for each scenario, were used the results of preliminary variant computational analyzes, engineering assessment of the initial and boundary conditions influence to the results, as well as experience in performing similar work. Thermal-hydraulic analyzes were performed using a computer code RELAP5 using a reactor model with a detailed breakdown of the downcomer and engineering code GRS-MIX to account for stratification in reactor downcomer. The results of analyzes showed that the selected initiating events lead to an intensive cooling down of the reactor pressure vessel and the internals. For scenarios leading to asymmetrical cooling, a different configuration of the ECCS was considered. For scenarios leading to a general cooling down of the coolant, the rupture location was chosen in such a way as to obtain maximum cooling down when the ECCS pumps operate in non-emergency loops. As a result of performing thermal-hydraulic analyzes of the initial events were determined boundary conditions for strength analysis performing. These boundary conditions were distribution of the pressure, the coolant temperature and the heat transfer coefficients.