Inspections at the Olkiluoto plant in accordance with the operational inspection programme in May–August 2023

During the second third of the year, STUK carried out four on-site inspections at the Olkiluoto nuclear power plant in accordance with the operational inspection programme.

Automation technology, 14–15 June 2023

The automation technology inspection focused on the automation technology systems, organization and instructions of all three Olkiluoto plant units. The inspection was focused especially on the development of automation technology configuration management and automation-related topics arising from the operational event reports processed by STUK. The inspection also dealt with matters related to the automation technology design organization and resources.

In the previous automation technology inspection in 2020, STUK drew attention to the configuration management of the plant units OL1/OL2. Based on the inspection, progress had been made. The findings of the 2020 inspection are described in the “Regulatory oversight of nuclear safety in Finland” annual report.

The automation technology measures for correcting errors reported in the operational event reports were relevant and the instructions were up to date. Resourcing of TVO’s automation technology has improved, but upcoming recruitments are needed due to factors such as retirements, and the availability of some experts remains challenging. Based on the inspection, TVO’s automation technology procedures comply with the set regulations regarding the inspected subject areas.

No requirements were made on the basis of the inspection.

Safety functions (OL1/OL2), 29–30 May 2023

The Safety functions inspection of the plant units OL1/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 target area of the 2023 inspection was “Fuel and reactor”, with special focus on reactor control systems and criticality safety assessment procedures. In addition, the human resources and competence management procedures of TVO’s reactor control were validated.

Based on the inspection, TVO has sufficient and professionally competent resources and clear procedures at its disposal in reactor control and criticality safety. Based on the inspection, the operation complies with the set regulations. On the basis of the inspection, STUK did not make any requirements.

Annual maintenance, 16 April–19 May 2023

The annual maintenance inspection assessed and validated the activities related to the implementation of the annual maintenance of the plant units OL1 and OL2. Several technical inspectors participated in the inspection, monitoring the activities, carrying out site tours, interviewing employees and monitoring progress of the planned work. During the annual maintenance, particular attention was paid to the procedures for the management of bulk parts and the use of safety-classified supplies (turvaluokiteltu tarveaine, TLTA) at work sites.

During the annual maintenance, no deviations were found in TVO’s operations that would have required immediate intervention from STUK. On the basis of the inspection, it can be concluded that TVO’s annual maintenance activities are in accordance with the requirements and have succeeded well – safely and in accordance with the plans drawn up in advance.

On the basis of the inspection, STUK presented one requirement. In accordance with TVO’s instructions, a TLTA class 4 chemical or consumable material requires case-specific instructions for use. During the plant tours carried out by STUK, it was not possible to verify the instructions or suitability of the use of the consumable material or chemical in use at the work sites. The requirement posed required TVO to develop its procedures regarding the guidelines for the use of a TLTA class 4 substance or chemical.

OL3 maintenance work management system, 7–9 June 2023

STUK carried out an additional inspection regarding the use of the OL3 plant unit’s maintenance work management system (KUPI) and ensuring that it is up to date. During the inspection, the procedures and situation related to the use of the system was surveyed using separate examples. The inspection was carried out unannounced, but TVO was informed about the inspection two days in advance in order for them to be able to reserve sufficient resources for the inspection.

The KUPI system has been in use for a long time at OL1/2 plant units. TVO is harmonising procedures and introducing the same system at OL3. The system has only been in use for a short time, but based on the inspection, its implementation and use has generally gone well. Establishing common operating methods still requires work and enhanced monitoring. With regard to separation plans, several entries have been created in TVO’s deviation and safety observation monitoring system. STUK monitors the status of corrective measures as part of its normal supervision.

On the basis of the inspection, STUK presented two requirements. The requirements required TVO to develop procedures for monitoring the overall situation of urgent malfunctions, as well as the availability of the current status of the work management system. During the Operational activity inspection of OL3 to be held in the autumn of 2023, STUK will verify that the measures to comply with the above requirements have been carried out.

Inspections at the Olkiluoto plant in accordance with the operational inspection programmein January–April 2023

During the first third of the year, STUK carried out six inspections at the Olkiluoto nuclear power plant in accordance with the operational inspection programme. Five of the inspections were carried out as an on-site inspections and one as a combination of remote and on-site inspection, a so-called hybrid inspection.

Operations (OL1/Ol2), 23–24 March 2023

The inspection focused on the operations of the plant units OL1 and OL2 verified the resource situation of the operating unit, operating unit’s indicators, processing of deviations, development proposals and safety observations and the preparations for unavailability of the digital user interfaces in the control room. During the inspection, a plant tour was carried out to the control rooms of the plant units.

Based on the inspection, the resource situation of the operating unit is good. For future needs, new instructor training groups have been set up at regular intervals. The operating unit was found to have systematic procedures for processing deviations, development proposals and safety observations and for monitoring measures. The operating unit uses several indicators that include both safety and usability issues. The indicators are used to monitor, for example, issues that increase the load of operators and the number and situation of faults affecting the operation.


The plant tour targeted at the main control rooms of the plant units OL1 and OL2 verified that the operating shifts know the procedures and instructions in the event of faults in the digital user interfaces. In addition, it was investigated how well the operating shifts are familiar with the updated instructions in the event of a reactor surface measurement fault, where the measurement shows an unnecessarily high reactor surface. Based on the inspection, appropriate instructions were available for the aforementioned fault situations, and the operating shifts were well familiar with the relevant procedures.


The operating procedures of TVO, verified by the inspection, comply with the set regulations. On the basis of the inspection, STUK did not make any requirements.

Fire protection, 25–26 April

The fire protection inspection assessed the effectiveness of TVO's fire protection arrangements. The inspection focused in particular on the resources of the plant fire brigade and the induction of new employees, which were identified as challenging areas in previous inspections and other STUK supervision. A plant tour was carried out for the OL3 plant unit in connection with the inspection.

Based on the inspection, TVO has solved the worst resource shortage of the plant fire brigade.

New employees have been recruited and the induction has progressed so that the new employees are now working in shifts. There is still a shortage of two employees and recruitment is still ongoing. The induction arrangements have been well implemented. Positive feedback has been received especially about the fire simulator used in the training.

The report on the ignition at the OL1 emergency diesel generator replacement site in January 2023 was discussed during the inspection. The ignition extinguished spontaneously and there was no threat to nuclear safety. The report revealed shortcomings in the operations of the subcontractors, for which TVO correctly identified corrective measures.  

During the plant tour, shortcomings were found in the marking of storage areas and in the earthquake fastenings of movable property. Otherwise, the cleanliness level of the plant was high and no additional fire load was observed.

TVO's fire protection arrangements, which were verified by the inspection, comply with the set regulations. On the basis of the inspection, one requirement was made regarding the shortcomings found in the earthquake fastenings at OL3. STUK will monitor the development of the resource situation of TVO's fire brigade as part of its normal supervision.

Radiation protection, 7–9 March 2023

The radiation protection inspection was targeted at learning from operating experiences in the radiation protection area of responsibility. In addition, the coverage of the radiation protection instructions and the measurement results obtained from alpha measurements were reviewed. Other topical issues in radiation protection were also discussed.

In TVO's radiation protection organization, the handling of operating experiences is appropriate. However, there is no systematic procedure for processing operating experience data from different areas of responsibility as a whole. A common situational picture of operating experiences and potential problem areas is formed through informal discussions, which TVO has found to be a functional procedure in practice.

The test runs of Olkiluoto 3 have progressed as planned with regard to radiation protection. During the plant tour, radiation measurement arrangements were examined in the Olkiluoto storage buildings.

Based on the inspection, TVO's radiation protection procedures comply as a whole with the regulations. On the basis of the inspection findings, three requirements were made for TVO to take action in certain areas. The requirements concerned the development plan related to the use of a Radiation Safety Expert, the completion of the ALARA action plan and the targeting and updating of the radiation protection guidelines

Security arrangements, 25–28 April 2023

The topics of the security arrangement inspection were recent developments and other topical issues, information security, including supply chain management, the final disposal repositories for power plant waste, practical operations and operating experiences, which were verified during the plant visit. An information security inspection related to annual maintenance was carried out in connection with the inspection. 

TVO is currently carrying out a comprehensive security arrangement assessment and development project. In addition, projects to improve and update security control systems as well as individual immediate actions are underway. 

The inspection made a number of positive observation and two requirements.

Power plant waste, 28–29 March 2023

The inspection of the power plant waste was primarily focused on the waste management arrangements of plant unit OL3. In addition, the planning of nuclear waste management measures as a whole, the adequacy and competence of nuclear waste management personnel and the timeliness of the guidelines were reviewed. The inspection covered the findings of the previous inspection as well as developments and significant events since the previous inspection. The condition of the waste treatment and storage facilities, the radiation levels of the facilities and the classifications and markings were verified during the plant tour that was included in the inspection.

Based on the inspection, TVO has sufficient resources at its disposal to manage the waste of the power plants. The responsibilities and powers of the clerical workers had been clarified and the deputies for different tasks had been defined. TVO did not present a summary of the status of the OL3 guidelines and the final safety analysis report during the inspection. Communication with TVO's radiochemistry laboratory had improved compared to the time of the previous inspection. Since the commissioning of OL3 waste management systems, there have been faults which have been repaired. According to TVO, the detected faults have been small, with the exception of faults that occurred in the evaporator in autumn 2022. Repairing faults has sometimes taken a long time due to, for example, the long delivery times of spare parts. At the time of inspection, the systems were operational.

Based on the inspection, the management of power plant waste complies with the set regulations. On the basis of the inspection, STUK did not make any requirements.

PTO readiness verification, 2–3 March 2023

The inspection of the plant unit OL3 verified the readiness of the plant's organization and operations to move from the commissioning test phase to the commercial use phase (so-called PTO phase). The objective of the inspection was to verify the readiness of TVO's organization to take the OL3 plant over from the plant provider in its entirety. The inspection dealt with the actions of TVO's management in relation to the change of responsibilities, the identification of risks related to the organization's operations, the level of the organization's competence and the readiness of the management system. In addition, the ability of TVO to manage the plant and the situation regarding the closure of cases that are still pending were reviewed.

On the basis of the inspection, the readiness for commercial use could not be fully verified, as many issues were still pending. For example, the agreement on the guarantee organization and procedures between the plant provider and TVO was still pending. However, progress had been made in many areas in recent months and TVO was found to have comprehensive procedures in place to monitor the progress of preparedness.

During the inspection, attention was paid to TVO's maintenance resources, for which there were still deficiencies in terms of both the number of personnel and the familiarity of the personnel, including systems that are important from the point of view of safety, in relation to the target state set by TVO. STUK considered it important that co-operation agreements with the plant provider and other subcontractors compensate for the situation. 

On the basis of the inspection, STUK did not make any requirements. STUK will continue to monitor the activities of TVO's organization as part of its normal supervision.