Extended general overhaul of Mochovce NPP Unit 1

24/03/2017
Extended general overhaul of Mochovce NPP Unit 1
The overhaul began on 25 March. The extended shutdown takes place once every eight years.

In order for a car to work safely and not break down we must have it monitored, maintained and refuelled regularly. The same applies to the safe operation of a nuclear power plant, which requires regular general overhauls. During such shutdowns revision and maintenance activities are carried out, new projects are implemented, equipment is replaced and partial refuelling is also performed. The scheduled extended general shutdown of unit 1 of EMO began on 25 March.

Why extended?

The reason is that this kind of shutdown contains the largest scope of miscellaneous activities (reviews, replacements, repairs and similar) on selected equipment of the reactor unit. The extended shutdown takes place once every eight years. The current shutdown also includes comprehensive fuel unloading which is connected with monitoring of the reactor’s pressure vessel. 

Activities of such significance involve the participation of hundreds of employees at our power plant as well as from EBO V2, not to forget more than 700 contractor employees.

To be able to launch the works involved in the extended shutdown, we first of all had to shut down and cool the reactor unit. Then we could proceed with other operations, such as reactor disassembly and fuel unloading.In addition to these activities, a great number of other scheduled works are being carried out.

For instance, investment activities include the addition of 400kV switches, seismic revision, replacement of electric switchgears and modernisation of safety systems. The general overhaul will adjust part of the reactor control and protection system – the System of group and individual management of emergency control rod assemblies of the reactor. 

This equipment enables a monitored reactor start-up from its shutdown status, control and sustainment of the desired reactor performance level as well as the reduction in its performance or full-scale shutdown. Simply said, this represents the replacement of one of the most important pieces of equipment in the reactor control and protection system having a great impact on nuclear safety and unit availability.As regards the main control room, this will undergo renovation and upgrading of the equipment’s control elements.

Before the end of the shutdown further work must be carried out, including loading of the inner parts of the reactor and of fuel, reactor assembly, tightness tests of the hermetic zone, heating up the unit, regular hydraulic tests and, once all these operations have been successfully carried out, the unit’s start-up will be launched.

In all these maintenance interventions the safety of all staff participating in the shutdown is of the utmost importance, as is also the prevention of dropping foreign material into the open equipment.

Following a successful completion of the extended shutdown of EMO Unit 1, the cooling towers will once more “steam away” and our power plant will continue to safely generate the energy we need for our lives.