Author(s): A. Sirca; R. Rajar

Linked Author(s): Andrej Širca

Keywords: Thermal load; Sava River; Run-of-the-river HPPs; Temperature monitoring; Mathematical modeling

Abstract: A 58-km stretch of the Sava River in Slovenia has been studied since 1998 for possible additional thermal load resulting from construction of a HPP chain. 1D and 3D mathematical models were applied and field measurements were analysed. Six run-of-river HPPs were planned and five of them have already been completed on the 58 km long reach of the lower Sava River in Slovenia. Among environmental impacts, also influences on thermal load of the river have been studied between 1998 and 2015. A special emphasis was given on the site analysis of the only Slovenian NPP in Krško, which is situated in the area of the fifth reservoir of the HPP chain. The NPP is cooled by the Sava River. A first integral study of the Sava River was performed in 2003, which forecasted river water temperatures for different stages of the HPP chain development by simplified 1D mathematical models. These models were verified by comparison with results of a 3D model (PCFLOW3D) and by measured data. Following the advancement of the chain construction, automated temperature monitoring of the entire reach of the lower Sava River was established in 2008. After a partial completion of the HPP chain with Blanca stage in 2009, it enabled a review of forecasted river temperature results for the first three upstream reservoirs. At that time, also some meteorological and hydrological influences of supposed climate change were addressed. In 2015, a final analysis of the Sava River thermal load was made for the purpose of obtaining an approval for the Brežice HPP from the Slovenian Nuclear Safety Administration, which is responsible for operation of the Krško NPP. The following conclusions of the Study are essential: Mean monthly river water temperatures will not change following the HPP chain construction. The anticipated changes are of a magnitude order of a simplified 1D model-based error. In the last decade, natural increases of the mean river water temperatures at the beginning of the section were of the same magnitude order as the potential increases due to reservoirs located in the section between the confluence and the Blanca HPP. During hot meteorological events the river water temperatures at the NEK intake will be equal to or lower than those, which would occur under equivalent hydro-meteorological conditions, yet without the reservoirs constructed in the Sava River valley. Changes in natural conditions as regards thermal loads of the Sava River were confirmed by various analyses.

DOI: https://doi.org/10.3850/978-981-11-2731-1_192-cd

Year: 2018