Planned outage execution is like a great piece of art

Planned outage execution is like a great piece of art
Outage of a nuclear power plant is a highly demanding event. Its execution is a masterpiece of hands and minds of people participating in it.

Outage of a nuclear power plant unit is a highly demanding event. Its execution can be compared with a masterpiece of hands and minds of people participating in it. But not only the ones planning this act, but mainly those ensuring its coordination and execution. This is like a "planning university" of tens of thousands tasks and coordination of many people during the outage.

"Outage means huge responsibility and lot of work for people, not only for those working on the units that are offline, but also for those at the operating units. The workers work in daily 12-hour shifts, some activities are continuous," says Mr. Ľubomír Novanský, sponsor of outage management process and NPP support Manager.

Refuelling and maintenance

Outage is required first of all to change portion of fuel in the reactor once in twelve months – usually one fifth. We need highly reliable devices to minimize possible shutdowns due to their failures. Therefore, each outage is also connected with preventive maintenance, service and inspections of equipment that cannot be done during normal operation.

Planned duration of outages is connected with work demand. When we plan inspection of reactor internal part, we have to remove all fuel and reactor internals. This type of outage is called “extended”, takes longest time and is done once in 8 years. Every 4 years we perform medium outage, when we perform external inspection of the reactor vessel. And in the meantime we have three short outages. All these outages are done on our two units in Mochovce and two in Bohunice in a way preventing combination of longer outages within the same year. Even though we have not yet commissioned units 3 and 4 in Mochovce, we already started planning their outages.

Planning, planning, planning

Planning of outages is based on their optimization, i.e., how to do standard outages in shortest possible time. Currently, the shortest outage is planned for 18 days. This duration is based on matter and time optimization of its individual stages that include own shutdown, dismantling of reactor, refuelling, reactor re-assembly and start-up.

Ľubomír Novanský likes painting in his free time.

Ľubomír Novanský likes painting in his free time.

Alternation and planning of extended, mid-term and short outages are planned with 10-year advance. We search the ways to shut down the power plant at times of low electricity prices, but, at the same time, to ensure maximum effective use of fuel. We have to care not to overlap the outages due to restricted workforce available for performance of works. Outage preparation starts 12 months before its actual commencement, i.e., during the preceding outage. So, this is a never ending story. Workers planning individual outages hardly finish with planning of the first one, and already continue with reparation of the next one.  At this time they define what would like to be done during the upcoming outage, and also how and who would do it.

Execution and coordination

Standard outage includes approx. 30 thousands activities. Each of them must be scheduled, as this also determines planning of capacities. It is also necessary to consider unexpected situations. And if something like this happen, the most efficient way is to do it immediately and not to postpone anything. This is the masterpiece we are talking about – coordination of outage execution. Managing collisions and unexpected situations is a real art.