Uprate project under way at Slovak units

Operator Slovenské Elektrárne shut down one of the two turbine generators at Mochovce unit 2 on 15 August. After allowing it to cool down, the company started to dismantle the high-pressure and low-pressure parts of the turbine yesterday. "This kicked off the most important part of the large and demanding modernisation project to increase the nuclear power plant units' efficiency," it said.

The modernisation will involve the replacement of the complete high-pressure part and flow sections of low-pressure parts of both turbines at Mochovce 2 with modified and more efficient ones. Turbine oil regulation and control will also be changed due to the electronic turbine regulator replacement. In addition, the work involves the overhaul of valves, fittings, flaps around turbines, replacement of moisture separators upstream of turbines and feedwater nozzles, and the replacement of current and 15.75 kV voltage converters behind generators. The replacement will continue with 400 kV unit transformers and other works in electric and instrumentation & control systems.

Unit 2 is scheduled to start supplying more electricity to the grid from November. In the spring of 2021, the modernisation of the turbine generators at unit 1 is also expected to be completed.

Slovenské Elektrárne said it expects the uprates at Mochovce 1 and 2 - which will increase their power output by about 7% - to be achieved without increased fuel costs, personnel costs and with reduced maintenance costs in coming years.

"The turbine's output at a cooling water temperature of 21.5ºC will be 250.72 MWe, but the current technology enables even further increase in the unit's efficiency," said Martin Mráz, director of the Mochovce plant. "Once the turbines are modernised, we will perform warranty measurements, which will show us potential reserves for further possible increase in the output of the secondary circuit equipment - particularly separators, high-pressure and low-pressure heaters. Service life of the turbines after their modernisation will be 40 years."

Slovenské Elektrárne carried out similar modifications at the Bohunice V2 nuclear power plant, where electrical output was increased in 2010.