NEK is ready for the first regular outage in the extended operating period

On Monday, 1 April, after the shutdown of the Krško Nuclear Power Plant (NEK), a regular outage will begin, which will last a month. We will replace the fuel during this period and conduct preventive inspections, maintenance works, and surveillance tests. We continue introducing constant technological improvements even in the first outage during the power plant's extended operating life. In the 33rd operating cycle, which began after the outage on 7 November 2022, we fulfilled all administrative requirements for long-term operation. We obtained environmental consent for the extension of operation until 2043. With the first transfer of spent nuclear fuel to spent fuel dry storage, we completed a large-scale technological upgrade and thereby increased the power plant's resistance to unlikely extreme natural and other phenomena and fulfilled the decision of the Slovenian Nuclear Safety Administration. The third periodic safety review (PSR3) confirmed that NEK meets the conditions for extending the validity of the operating permit. The implementation of the plan of changes and improvements, which we must finish by the beginning of December 2028, is already underway.

In strict compliance with operating and environmental restrictions, NEK produced 7.735 billion kilowatt hours of electrical energy in the current fuel cycle. Even during last summer's water floods, it confirmed its resistance and high operational reliability; it was operating at full power. The high safety culture, professionalism, and commitment were also confirmed by employees and business partners last October when, during an emergency outage, they effectively eliminated a deviation in the safety injection system. Due to the emergency outage, production in the 33rd fuel cycle was about 8 percent lower than planned.

High-quality outage work is the basis for reliable operation.

After thorough preparations, on Monday, 1 April 2024, with the disconnection of the power plant from the power grid, a regular outage will begin, which is expected to last until 1 May. More than 4,000 work orders are prepared; we are planning 30,000 activities. Since this will be the first regular outage in the extended operational life of the power plant, it will be essential to check the impact of aging on components, systems, and structures, along with fuel change, standard surveillance, maintenance, and updating of equipment.

When replacing 53 fuel elements with fresh ones, the main works will include preventive maintenance of technological equipment, inspection of the condition of technological structures, and checking pressure boundaries per the associated programs, which cover all safety equipment and its assemblies. It is a process of checking and upgrading equipment to ensure reliability. Most of the equipment installed in a nuclear power plant can only be maintained when the plant is shut down and cooled down.

All outage works are managed and supervised by NEK employees; during the outage, we are also joined by external contractors from Slovenia and Croatia and contractors of specific works in the nuclear industry from the international environment. Again, more than 1,000 contractors’ workers will participate in NEK this year. The Slovenian Nuclear Safety Administration will supervise outage works, and authorized organizations will also monitor them and give their expert opinion after the outage.

Major Maintenance Activities:

- overhaul of the connecting valve on the component cooling system,

- overhaul of the motor-driven auxiliary feedwater system pump,

- replacement of the compensation connection between the condenser and the turbine,

- overhaul of the main electric generator,

- servicing and changing the oil on the containment polar crane,

- laser measuring of the reactor vessel flange,

- replacement of the INCORE guide tubes,

- eddy current non-destructive examination of steam generators tubes,

- additional and regular inspections of the welds at pipes connecting to the primary loop,

- inspection of relief valves on both moisture separator reheaters,

- partial replacement of cables of the reactor building lighting systems,

- sludge lancing of steam generator tube bundles,

- eddy current examination of the component cooling heat exchanger,

- sealing of the main transformer seal oil system.

We maintain a policy of continuous technological improvements.

We upgrade the equipment at NEK based on our own and foreign operating experience, administrative requirements, and standards. This increases nuclear safety and the power plant's availability and capacity.

With the first outage in the extended operating period, we continue the policy of power plant management by introducing constant technological improvements. Thus, we will carry out 16 modifications in this year's outage. To support long-term operation, we will also replace the second heat exchanger in the component cooling system (the first one was replaced in the 2022 outage), update the control rod power system, and replace the control rod position indicator.

To improve thermodynamic efficiency, we will replace the first two rows of stator blades of the high-pressure turbine installed in 2022 with the associated new throttle ring, enabling the turbine to operate at its optimal operating point.

In the NEK switchyard, we will replace the secondary equipment in the 400-kilovolt fields and equip both transformer fields with two new field computers.

Better suction conditions of the cooling tower pumps will enable greater operational efficiency of the towers. Installing an ultrasonic level meter in the primary coolant loop and a unit transformer monitoring system will also improve operational control over the systems.

In line with our commitment to ensuring high occupational safety and health, we will carry out upgrades to provide safe access and safe working at height in the reactor building's most exposed and frequently used locations.

NEK, during decades of its operation, met the expectations of the pioneers of nuclear technology.

At the beginning of December, it will be 50 years since the symbolic start of the power plant construction. In August 1974, a location permit was issued, and the main contract for the plant construction and the fuel supply was signed. The power plant was built earlier than seven years; its trial operation began in the fall of 1981. During the decades of operation, we have built a competent and committed team who ensures high plant efficiency through responsible management, good maintenance, and well-thought-out modernizations. We are pleased to note that we have met and probably exceeded the expectations of the visionary pioneers of nuclear technology in our area, as NEK will provide consumers in Slovenia and Croatia with electrical energy at an acceptable price for at least another two decades. The predictability and stability of its operation in all weather conditions are essential for customers and the reliable operation of power systems. At the same time, NEK stabilizes power transients in the network with its sizeable rotating mass. Its low carbon footprint helps preserve the natural environment and meet environmental commitments.