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Influence of cooling water temperature on performance of EPR nuclear power plant

100%

Laskowski R. , Smyk A. , Uzunow N.

Rynek Energii

2021

tom Nr 1

57--62

The paper analyses how cooling water temperature affects the performance of an EPR nuclear power plant. At higher cooling water temperatures, the power output and efficiency of the system are lower. One of the factors that influence the performance of a nuclear power plant is its geographical location, since mean water temperatures are lower in the northern part of Europe than in its southern part. Although the nature of changes and the trend related to the effect of cooling water temperatures are known, the quantitative effect has to be determined on a case-by-case basis. A power plant with most likely pressurized water reactors (PWR) is to be built in Poland, which is why a state-of-the-art EPR pressurized water reactor design was selected as a subject of the present analysis. Depending on the location of this power plant, various cooling water temperatures to cool down its condensers, and therefore various operating conditions of the cooling system can be achieved. It is important to note that due to the smaller available enthalpy drop in the turbine of an EPR unit compared to the turbines of conventional units, steam cooling conditions play a vital role in this case. To analyze how the temperature affects the performance of the power unit, a model of an EPR power plant was developed using the Ebsilon software.

W artykule dokonano analizy wpływu temperatury wody chłodzącej na osiągi elektrowni jądrowej z reaktorem typu EPR. Wraz ze wzrostem temperatury wody chłodzącej następuje spadek mocy i sprawności układu. Osiągi elektrowni jądrowej zależą m.in. od położenia geograficznego, ponieważ na północy Europy średnie temperatury wody są niższe niż na południu Europy. Charakter zmian i tendencja wpływu temperatury wody chłodzącej są znane natomiast ilościowy wpływ należy określać indywidualnie dla każdej elektrowni. W Polsce ma zostać wybudowana elektrownia najprawdopodobniej z reaktorami PWR, dlatego do analizy wybrano jedną z najnowszych technologii z reaktorami typu wodno-ciśnieniowego typu EPR. W zależności od lokalizacji tej elektrowni możliwe do osiągnięcia są różne wartości temperatury wody chłodzącej skraplacze EJ a więc i różne warunki pracy układu chłodzenia. Warto podkreślić, iż ze względu na mniejszy rozporządzalny spadek entalpii w turbinie bloku jądrowego EPR, w stosunku do turbin bloków konwencjonalnych, warunki chłodzenia pary odgrywają tutaj istotną rolę. W celu przeprowadzenia analizy wpływu tej temperatury na osiągi bloku został stworzony model elektrowni z reaktorem EPR w programie Ebsilon [1].

Selected aspects of the choice of live steam pressure in PWR nuclear power plant

75%

Laskowski R. , Smyk A. , Jurkowski R. , Ancé J. , Wołowicz M. , Uzunow N.

Archives of Thermodynamics

2022

tom Vol. 43, no 3

85--109

In commercially available generation III and III+ PWR (pressurized water reactor) reactors, pressure of steam produced in steam generators varies in a relatively wide range from 5.7 to 7.8 MPa. Therefore, it is important to ask which value of steam pressure should be used for a specific unit, taking into account different location conditions, the size of the power system and conditions of operation with other sources of electricity generation. The paper analyzes the effect of steam pressure at the outlet of a steam generator on the performance of a PWR nuclear power plant by presenting changes in gross and net power and efficiency of the unit for steam pressures in the range of 6.8 to 7.8 MPa. In order to determine losses in the thermal system of the PWR power plant, in particular those caused by flow resistance and live steam throttling between the steam generator and the turbine inlet, results concerning entropy generation in the thermal system of the power plant have been presented. A model of a nuclear power plant was developed using the Ebsilon software and validated based on data concerning the Olkiluoto Unit 3 EPR (evolutionary power reactor) power plant. The calculations in the model were done for design conditions and for a constant thermal power of the steam generator. Under nominal conditions of the Olkiluoto Unit 3 EPR power unit, steam pressure is about 7.8 MPa and the steam dryness fraction is 0.997. The analysis indicates that in the assumed range of live steam pressure the gross power output and efficiency increase by 32 MW and 0.735 percentage point, respectively, and the net power output and efficiency increase by 27.8 MW and 0.638 percentage point, respectively. In the case of all types of commercially available PWR reactors, water pressure in the primary circuit is in the range of 15.5−16.0 MPa. For such pressure, reducing the live steam pressure leads to a reduction in the efficiency of the unit. Although a higher steam pressure increases the efficiency of the system, it is necessary to take into account the limitations resulting from technical and economic criteria as well as operating conditions of the primary circuit, including the necessary DNBR (departure from nucleate boiling ratio) margin. For the above reasons, increasing the live steam pressure above 7.8 MPa (the value used in EPR units that have already been completed) is unjustified, as it is associated with higher costs of the steam generator and the high-pressure part of the turbine.