Inspections at the Olkiluoto nuclear power plant

STUK carries out inspections to oversee the operation and use of the Loviisa nuclear power plant. The periodic inspection programme covers safety management, main operational processes, procedures and technical acceptability of systems. 

STUK draws up a plan for the inspection, setting out the subject of the inspection and any preparatory actions required of the licence holder. The result of the inspection and the resulting requirements are set out in the inspection report.

Periodic inspections

Below are summaries of the inspections carried out by STUK in year 2024 in accordance with the periodic inspection programme for the Olkiluoto nuclear power plant.

Safety functions (OL3), 6–8 November 2024

The inspection focused on the safety function “Fuel cooling and residual heat removal” and the associated systems. The status of the systems was reviewed with the help of system responsibility reports and information was verified from TVO’s information systems. On the basis of the inspection, the systems function well and meet the acceptance criteria under the design criteria.

The licensee’s procedures and competence to ensure the design-based status and operational capability of the safety function and the systems implementing it are good. The situation is good with regard to the instructions, spare parts, adequacy of resources as well as performance and recording of periodic tests and the utilisation of operating experience, but there is still room for improvement. Based on the inspection, TVO has the will and ability to further develop its operations.

Based on the inspection, STUK required TVO to initiate the necessary investigations to map the oscillating emergency cooling and removal of residual heat system pipelines. In addition, the erosion risk areas of the pipelines of the diesel-secured intercooling system of the safety and process systems and the thickness measurements carried out on them must be added to the pipeline condition monitoring programme to be submitted to STUK for information. Based on the inspection, STUK also requires TVO to improve the systematic recording of periodic tests. The documentation must be clear and up-to-date in order to ensure the safety of the plant.

OL3 operations, 1 October 2024

The inspection focused on the operation of the Olkiluoto 3 plant unit (OL3). The objective of the inspection was to investigate and verify, for example, the procedures related to periodic tests and work permit practices as well as the situation of the OL3 operating division.

Based on the inspection, TVO has taken measures to manage the overall situation of periodic tests. TVO still has different procedures for managing the monitoring of tests. Shared and unambiguous operating methods would make it easier to manage the entity, to give instructions and to monitor compliance with the instructions. STUK monitors TVO’s development measures and the creation of procedures as part of its normal monitoring.

On the basis of the inspection, OL3's work permit practices are at an acceptable level. STUK finds the instructions on the practices of the work permit office, which clarify the work permit office’s operations, as a good measure. With regard to the recording of observations, STUK considers it important that they continue to be recorded at a low threshold. The interfaces and communication between the different parties were identified as a challenge. This issue needs to be taken into account in the future. For smooth work management, it is important that all parties know how to operate and use the existing information systems.

With regard to external operating experiences, events related to the use of other facilities are systematically processed in the OL3 operating organisation.

Based on the inspection, the condition of the OL3 operating unit is at an acceptable level: the operations have been appropriate during power operation and during the first annual maintenance. The indicators used by the OL3 operating unit support the creation of a situational picture. At the OL3 operating unit, personnel planning is forward-looking and the lessons learned from the first annual maintenance of OL3 have been taken into account in the planning. Based on the inspection, the resources and organisation of the operating unit are appropriate.

The inspection did not result in any requirements presented by STUK.

Safety functions (OL1/OL2), 3–4 June 2024

The inspection of the plant units OL1 and OL2 assessed the procedures by which TVO ensures the validity of the design principles of the systems used to implement the safety functions and the compliancy of the systems. The 2024 inspection was targeted at systems implementing fuel cooling and residual heat removal, focusing on the cooling system of the reactor building’s fuel pools and the distribution system of demineralized water. A plant tour was carried out at the OL1 plant unit in connection with the inspection.

Based on the inspection, the cooling system of the fuel pools is in good condition and the documents and instructions were found to be up-to-date. The status of the systems' spare parts was found to be in good order. The most significant ongoing modification project for the fuel pool cooling system is the replacement of the plate heat exchanger components. The distribution system for demineralized water was also found to be in good condition, and TVO has taken care of the maintenance of the system and the associated reserve water tanks.

The periodic tests of both systems examined were found to have been carried out in a timely and approved manner. During the plant tour, it was observed that the rooms housing the systems were clean and tidy.

The inspection did not result in any requirements presented by STUK. The systems examined and TVO’s procedures were found to meet the set requirements.

Annual outage (OL1/OL2), 28 April – 29 May 2024

The inspection of the annual outages of Olkiluoto plant units 1 and 2 in 2024 assessed the operations and procedures of TVO and its subcontractors during the annual outages. Supervision was focused on areas such as operational safety, mechanical equipment, electrical and automation technology and radiation protection. The special cross-technical topics selected for the 2024 inspection were the Operational Limits and Conditions (OLC) and fire safety.

TVO was found to have appropriate procedures in place for monitoring the OLC compliance of the plant units and for carrying out periodic OLC tests during annual outages. With regard to the acceptance criteria for the periodic OLC tests of electrical systems, minor differences were observed between the test instructions and the plant’s design criteria. STUK will continue to investigate the observation as part of its monitoring.

With regard to fire protection procedures, STUK’s inspectors made some observations that deviated from the fire protection instructions. The observations included open fire doors and an unmarked fire load. The most significant observation was the lack of hand-held fire extinguishers at one hot work station. Based on the inspection, it can be concluded that, despite some deficiencies, TVO’s fire protection arrangements during the annual outages are at a sufficient level.

With regard to radiation protection, STUK noted a localized increase in primary circuit radiation levels observed at the OL2 plant unit. The reason for the increase in radiation levels could not be determined during the annual outage. During the annual outage of OL2, TVO did not have equipment in use that could have obtained nuclide-specific information directly from the surfaces of the systems. In accordance with current practice, measurements enabling nuclide-specific analysis of surfaces are carried out every four years. STUK required TVO to assess whether the current procedure for nuclide monitoring and the frequency of measurements are appropriate.

On the basis of the inspection, it can be concluded that TVO's annual outage activities are in accordance with the requirements and have been carried out well; safely and in accordance with the plans drawn up in advance. The inspection presented one requirement related to the implementation of nuclide-specific monitoring measurements of primary circuit surfaces.

Annual outage (OL3), 2 March – 16 May 2024

The inspection focused on the annual outage work of TVO’s Olkiluoto 3 unit. The inspection focused on evaluating the safety of the plant, work permit practices, waste management and radiation protection, among other things. During the first annual outage, safety-relevant work included inspections of the nuclear fuel and the reactor’s primary circuit and its most important components.

Based on the inspection, it was found that TVO was successful in organising maintenance work and that the operations were well thought-out and systematic. Unexpected failures and other setbacks were resolved without compromising safety requirements. STUK found that TVO allocated the necessary amount of time for the implementation and planning of the annual outage and prioritised safety.

Based on the inspection, some challenges emerged in TVO’s operations, such as unwarranted alarms that put a strain on the personnel. TVO has initiated an investigation concerning the causes of these alarms. Deficiencies were observed in the work permit practices, such as the incorrect timing of work and the lack of work permits. TVO has also launched investigations to improve these practices. Waste management worked well and the waste sorting locations were clean and clearly marked. TVO is also planning to improve its waste management capacity. With regard to radiation protection, the situation was mainly good, although some markings and the cleanliness of workstations showed room for improvement.

During the annual outage, TVO transferred all the nuclear fuel from the reactor to a separate fuel building and inspected the fuel rod clusters. During the inspections, TVO detected foreign objects in multiple fuel rod clusters and submitted a report on this to STUK. The origin of the foreign objects is still being investigated. STUK requires TVO to submit a report on further investigations of the foreign objects and possible measures before the next annual outage.

Based on the observations and reports made during the annual outage, STUK presented requirements on updating the instructions based on experiences from the annual outage, investigating the origin of the foreign objects, improving anticipation in procurement and work planning and clarifying the protocol procedures. In addition, TVO must ensure that the resources for mechanical maintenance are sufficient.

Nuclear security, 19–21 March and 25 March 2024

The inspection of TVO’s security arrangements covered both physical security arrangements and information security. In connection with the inspection, a plant tour was carried out, in which the annual outage of the OL3 power plant unit was verified from the perspective of safety arrangements.

TVO has planned a comprehensive safety arrangement development project. Changes in the operating environment, situational information, implementation decisions of the YVL Guides, international IPPAS assessment, independent assessment by the Finnish authorities and the regulations are used as the starting points of the project. Continuous improvement measures are carried out at all times, including in the areas of the insider threat prevention programme, access control and security inspection arrangements, development of the security organisation’s operational capacity, etc. The information security development project is a comprehensive project that raises the maturity level of information security and defence against cyber threats.

Based on the inspection, no new requirements were presented. However, STUK’s two previous requirements related to supply chain security management and access rights management remained in force.

Management of a potential power uprate project, 9–10 April 2024

In the 2024 operational inspection programme, STUK carried out an inspection of TVO’s potential power uprate project for OL1 and OL2 units as a special topic. In the project, TVO is investigating the possibility of uprating the reactor power of the OL1 and OL2 plant units. TVO will make a decision on the implementation of the project later.

At this stage, STUK’s inspection focused on TVO’s project management procedures. The purpose of the inspection was to proactively identify possible factors that could cause safety challenges as the project progressed. The inspection found that TVO has developed the project procedures of the power uprate project using both its own experiences and lessons learned from abroad, especially from Sweden. The project is planned to be implemented in a TVO-led manner without extensive “turnkey” agreements, which gives TVO better control and responsibility for the implementation of the project. STUK did not detect any significant deficiencies in project management during the inspection.

STUK did not present any requirements based on the inspection, but emphasized the importance of TVO’s continued careful project management and supplier monitoring. In conclusion, STUK assessed that TVO’s procedures in the management of the power uprate project have been appropriate and that TVO has demonstrated its ability to maintain a high level of safety during the project planning phase.

Radiation protection, 13–14 February 2024

The inspection concerning radiation protection was targeted at radiation protection, radiation measurement and release and environmental monitoring. The inspection covered all Olkiluoto plant units.

Radiation measurement was the special focal point of the inspection in 2024. In addition, the inspection reviewed, among other things, the storage of radiation sources and the use of international operating experience feedback in the topic of inspection concerning radiation protection and radiation measurements. The inspection included a tour of the plant to learn about the radiation measurement arrangements and the storage of radiation sources at the OL3 plant unit.

Based on the inspection, STUK concluded that TVO has procedures in place that enable high-quality operations in the topic of inspection concerning radiation protection and radiation measurement. The maintenance of the measuring equipment used for measuring radiation has remained at a good level, and the modernization of radiation measuring equipment has continued. Due to the deployment of the OL3 plant unit and Posiva’s new radiation measurements, the radiation measurement equipment is more extensive than ever before, which puts pressure on resource planning.

Based on the inspection, STUK presented two requirements concerning the updating of the safety assessment for the use of radiation and the leakage tests of radiation sources.

Chemistry, 6–7 February and 9 February 2024

The inspection concerning chemical operations focused on monitoring the water chemistry conditions and the flow of activities in the OL1, OL2 and OL3 plant units. The inspection assessed the adequacy and appropriateness of monitoring and the accuracy of the analytical methods used.

The monitoring of water chemistry and radiochemistry is at a good level for OL1 and OL2 plants. Any incidents have been monitored in a timely manner and elicited a response. During the inspection, TVO stated that it would update the chemical operating instructions (including sampling frequencies) for the shutdown and ramp-up before the start of the first annual outage of OL3. TVO said that it would take into account the experiences gained from the instructions during commissioning in its updated instructions. STUK noted that monitoring of the status of water chemistry should be carried out in accordance with the approved instructions presented in the Chemistry Handbook.

Based on the inspection, the condition of the continuously operating analyzers related to the monitoring of water chemistry and radiochemistry at the plants has been appropriately monitored. During the inspection, no problems were found in the flow of information between the maintenance department carrying out the periodic tests and the chemistry organisation using the equipment.

Based on the inspection, the quality control procedures of the laboratories responsible for monitoring the water chemistry and radiochemistry of the plants (including participation in proficiency tests, validation of equipment and analytical methods, representativeness of samples) are adequate. In addition, it was noted that the reorganisation of the chemistry organisations responsible for the monitoring of water chemistry and radiochemistry at the plants and the development of monitoring has not impaired the monitoring of the chemistry in the plant premises.

STUK did not make any requirements on the basis of the inspection.

Preparation for annual outage (OL3), 9–11 January 2024

The inspection was focused on the preparations for the first annual outage of OL3. The annual outage is scheduled to start in March 2024. The inspection reviewed, among other things, the situation of work planning and resources as well as preparation for changing situations during the annual outage. In addition, the annual outage training provided to operating personnel was verified.

Based on the inspection, TVO's preparations for the annual outage of OL3 are going well and the special features of the first annual outage have been taken into account. There are still uncertainties related to the annual outage, including the availability of spare parts. TVO should also be prepared for a situation where sufficient spare parts are not available. The safety significance of these possibilities must be assessed and, if the safety significance allows, any applications for exemptions from the Operational Limits and Conditions (OLC) concerning them must be prepared well in advance so that the priority of safety can be ensured and STUK can reserve the time required for the processing of the matters. With regard to the OL3 operating division, STUK stated that preparations for the upcoming annual outages have been carried out well. Any challenging work in terms of operation has been mapped out and annual outage issues were comprehensively taken into account in the operational training.

The annual outage schedule is highly optimized and tight. In the inspection, STUK pointed out that the schedule cannot be a determining factor in the annual outage planning and implementation; instead, safety must always be given top priority. STUK will monitor the implementation of this as part of the upcoming annual outage inspection.

On the basis of the inspection, STUK did not make any requirements.