The operating cycle at the Nuclear Power Plant (NPP) Krško lasts for 18 months after which an outage takes place. An outage is a planned shutdown of the power plant with the aim of replacing nuclear fuel, performing major maintenance activities, inspections, supervised tests, and technological upgrades called modifications. All of these actions ensure that the power plant can operate smoothly and reliably for another cycle.
The outage 2021 started on April 1 and lasted for 34 days. The main activities included replacement of almost half of the fuel elements in the reactor core and inspection of the reactor vessel, control rod guides, and steam generator pipes. The main modifications from the Safety Upgrade Programme were implementation of an alternative system for Safety Injection (ASI), an alternative system for Auxiliary Feedwater (AAF), an alternative system for Residual Heat Removal (ARHR) and Reactor Coolant Pumps’ (RCP) high temperature seals.
It is important to note that the outage 2021 was carried out in full and successfully despite the coronavirus pandemic. This was the result of protective measures which were undertaken such as wearing FFP-2 face masks, regular disinfection, automatic body temperature measurement at the entrance, testing at the parking lot, and organization of working hours over a 24-hour period to ensure a minimal number of people at the site at the same time.
Around 600 Krško NPP employees and 1900 subcontractors from Croatia, Slovenia and abroad participated in the outage. The University of Zagreb Faculty of Electrical Engineering and Computing (FER) is accredited by the Slovenian Nuclear Safety Administration to supervise safety-related outage activities. Our colleagues Davor Grgić, Siniša Šadek, and Štefica Vlahović from the Department of Energy and Power Systems were involved in the regulatory supervision of Emergency Control Room modification, changes of containment sump level monitoring, installation of a radioactivity monitor on the PCFV exhaust line, testing of fire protections system in the plant’s critical areas and main electrical equipment, testing of containment integrity, performance of Hydrogen passive autocatalytic recombiners (PAR) and performance of Emergency Core Cooling System (ECCS).