Mochovce NPP: Cold hydrotest completed at Unit 3

Mochovce NPP: Cold hydrotest completed at Unit 3
Slovenské elektrárne sucessfully completed the cold hydraulic test, one of the crucial parts of the nuclear power plant commissioning process.

Slovenské elektrárne sucessfully completed the cold hydraulic test of the Mochovce Nuclear Power Plant Unit 3. It was the first comprehensive testing, when reactor systems were operated for the first time together with auxiliary systems.

The cold hydrotest is one of the crucial parts of the plant commissioning process. Testing started in mid-July and took 38 days. The main objective of the cold hydrotest was to demonstrate leak-tightness of plant systems and components such as pressure vessels, pipelines and valves of both the Nuclear and Conventional Island and to clean main circulation pipes.

The primary circuit during the test was pressurized to 13.7 MPa (that is over 111 % of the operating pressure) and heated up to 120°C. Consequently, steam generators were tested from the secondary circuit side, as well as feedwater and live steam pipelines at the  pressure of up to 7.65 MPa (166 % of operating pressure).

„It is a key milestone that confirmed functioning of all tested components and took us closer to comissioning of the nuclear plant.“

Branislav Strýček
Director General of Slovenské elektrárne

The Cold Hydro tested all reactor coolant pumps of the primary circuit, main feedwater pumps of the secondary circuit, steam generators, pipelines, pumps and other components of the primary and secondary ciruits, including operation of a number of auxiliary systems. All components such as pipelines, valves, welds, and flange joints had to be inspected at exactly defined pressures. Important part of testing included the tightness test of the nuclear island containment that is made of up to 1.5 m thick reinforced concrete walls.

„I’m glad we have met the schedule specified for the Cold Hydro. The testing has shown high professional approach and readiness of the team responsible for the commissioning process, as well as good cooperation with our contractors.“

Francisco Morejon
Mochovce 3&4 Project Director

Mochovce Units 3&4 have an evolutionary design based on the pressurised water reactor VVER-440 V-213 with safety upgrades that make the power plant compliant with current stringent national and international nuclear safety  requirements. The capacity of each unit is 471 MW and will cover approximately 13% of electricity demand in Slovakia, with no greenhouse gas emissions.


Slovenské elektrárne is a leading producer of electricity in Slovakia and one of the largest in Central Europe. It operates two nuclear plants, 31 hydro power plants, two coal-fired and two photovoltaic plants with an installed capacity of 4,081 MW.The company generates 90% of its electricity without greenhouse gases emissions. 

In terms of ownership structure, Slovak Power Holding B.V. is the majority shareholder with 66% stake in Slovenské elektrárne; Slovak Power Holding B-V. is jointly owned by EP Slovakia B.V., a subsidiary of Energetický a průmyslový holding, a. s., and Enel Produzione S.p.A. The Slovak Republic is a minority shareholder owning 34% stake.