Commissioning of Unit 4 of the Mochovce 34 NPP has begun

On 22 May 2026, after verifying that all technical and legislative requirements have been met, the Nuclear Regulatory Authority of the Slovak Republic (ÚJD SR) issued Decision No. 229/2026, which permits the commissioning of the nuclear facility Unit 4 of the Mochovce 34 (MO34) nuclear power plant. On the day the decision was issued, the delivery of the decision by public notice began by posting it on the official notice board of the administrative authority, on the website of the authority, the central official notice board and temporary official notice boards of the administrative authority located in the affected municipalities for a period of 15 days. It was possible to file an appeal against this decision within 15 days from the date of its delivery. The deadline for filing an appeal expired on 24 June 2026. Since no objections to the issued decision were received by the authority within the specified period, ÚJD SR’s Decision No. 229/2026 entered into force on 24 June 2026, thus allowing the license holder to begin commissioning of the Unit 4 of the MO34 nuclear power plant.

After carrying out the necessary activities within the relevant program, the first fuel assembly was ceremoniously loaded into the reactor of Unit 4 on 29 June 2026 at 15:45, thus starting the commissioning stage of the nuclear facility.

During the administrative procedure, ÚJD SR consistently checked and evaluated all areas demonstrating the technical and qualitative readiness of Unit 4 for fuel loading. The investor had to demonstrate the readiness of the reactor unit for fuel loading and the start of active tests comprehensively in all assessed areas, from the completion of construction objects, through the completion of the assembly of technological systems, successful verification of project functions through a series of inactive system and integral tests, elimination of identified deficiencies and shortcomings, ensuring fire and radiation protection, environmental protection, to the readiness of personnel and operational documentation. The entry into force of the decision authorizing the commissioning of Unit 4 of MO34 without filing an appeal means that the UJD SR is considered a trustworthy authority that not only consistently and at a high expert level performs supervisory activities over all phases of the nuclear cycle, but also openly and transparently informs the participants in the proceedings and the interested public about the individual steps of the administrative procedure, and therefore the public has a high level of trust in the decisions of the authority.

After the complete loading of the fuel, the process of active reactor tests will begin, which is divided into the stages of physical and energetic start-up. The transition between the individual stages is subject to the approval of ÚJD SR, issued on the basis of the assessment of the progress and evaluation of the physical and energetic start-up tests and also the protocols of the facility’s readiness for the next stage of commissioning. The energetic start-up stage also includes a 144-hour full power demonstration run.

Only after completion of all prescribed tests, after their thorough evaluation, and after submission of the evaluation and relevant documentation, can the operator apply to ÚJD SR for a permit to operate Unit 4 and other related permits. Unit 4 of MO34 nuclear power plant with an installed capacity of 471 MW will provide approximately 13% of electricity consumption in Slovakia.