Operation of WWER-440 reactor units in the variable load regime

The Slovakian distribution system is among the minor ones. The highest load, about 4400 MWe, is attained in winter, the lowest (about 2300 MW), in summer. The structure of power sources in Slovakia is quite favourable: 2640 MW installed in nuclear, 2291 MW in fossil, 2438 MW in hydro and 661 MW in other sources. However, fuel costs of Slovak fossil-fuel fired power plants exhibit a constantly increasing trend, due to the price growth in the world market and to a high primary energy dependence of Slovakian economy. This stimulates a steady improvement in the use of nuclear, which has the second lowest fuel costs (after hydro). If nuclear sources are capable of providing the mandatory grid supporting services (frequency control, grid adjustment ...), then the demand for such services will increase in parallel to the growing fossil fuel prices in the world market. (author)