Oskarshamn 3 - Optimization after Power Uprate - A heat balance deviation analysis
Sammanfattning: Oskarshamn 3 has undergone a power uprate from 110% to 129.1% of original reactor thermal output in recent ended project PULS (Power Uprate with Licensed Safety). The main objective of this thesis have been to identify deviations in the power plant, explaining the differences in power output between designed and achieved power output after PULS. The investigation has been conducted with the use of classical thermodynamic heat balance calculations using computer software Probera. Prior to the heat balance calculations, a literature study has been done to investigate how wet steam turbines can be modeled with a special focus on the turbine capacity or wideness. The literature study led to an implementation of capacity model Beckmann in Probera which gave a better description of the plants performance and behavior off-design. The heat balance calculations showed that two major differences in the plant has occurred in comparison to what was designed: A wide HP-turbine which leads to a power loss in the region of 9-14 MW Higher condenser pressure than designed which leads to a power loss of 4-8 MW. The loss in power is however variable with a variable temperature in the cooling water, i.e. the Baltic Sea. At higher temperatures, around 15°C the loss in power output is none. The high condenser pressure can be explained by a variable blockage of tubes in the condenser with more tubes blocked with decreeing CW-temperature, which lead to the following reasoning about possible explanations: Problems with ejector system, off-design operation or design flaw. Choking of the steam and/or disturbed flow pattern on shell side. Loss of siphon effect on tube side which leads to a lower water level in water boxes and hence no water will be present in upper tubes. Air flow on tube side causing plugging two-phase flow and decreeing heat transfer coefficient. The explanations don’t stand alone but are even more plausible if one takes all or some of them into account. To confirm or to rule out some of the explanations, suggestions have been made to measure temperature and pressure over the intercondensers in the ejector system and to measure outlet temperature of strategically located tubes in the condenser.
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