Teollisuuden Voima Oy (TVO) owns two 840 MWe boiling water reactors Olkiluoto 1 (OL1) and Olkiluoto 2 (OL2) located in Olkiluoto.
In 1999 net production at OL1 was 7112 GWh and the capacity factor 96.9%. The annual outage and refuelling of OL1 was performed in May and lasted 8 days. The net production of OL2 was 7091 GWh and the capacity factor was 96.6%. The annual outage and refuelling of OL2 was in May and lasted 10 days. The total number of manhours of the outages was 147000. At peak, there were 671 outside workers.
In 2000 net production at OL1 was 7043 GWh and the capacity factor was 95.7%. The annual outage and refuelling of OL1 was performed in May-June and lasted 14 days. The net production of OL2 was 7091 GWh and the capacity factor was 95.5%. The annual outage and refuelling of OL2 was in May and lasted 14 days. The total number of manhours of the outages was 253000. At peak, there were 870 outside workers. Inspections made during the annual outages showed that the plant units are in good condition and that any faults or defects were minimal. The company policy is to keep the plant units as good as new.
During the year 1999 four events occurred that were classified level 1 on the International Nuclear Event Scale (INES). The events were:
All the events during the year 2000 were classified level 0 or below on the INES scale. In the first quarter of 2001, one deviation was observed and classified level 1. The bakelite pinions of several valve actuators had cracks and two of them were damaged mainly due to fatigue. Due to this observation bakelite pinions were replaced by brass pinions in the outer isolation valves of the core spray system of both units.
The preparation of the environmental management system based on the ISO 14001 standard was started in 1998 and accomplished at the end of 1999 when TVO was granted an international certificate based on this environmental management system.
The EIA-procedure, the investigation of the environmental impacts of a third reactor unit possibly to be built at Olkiluoto, was finalised in February 2000, when the contact authority, the Ministry of Trade and Industry gave its statement on the EIA report.
By the end of the year 2000, 3942 cubic meters of low and medium level operating waste has accumulated in Olkiluoto. Most of this waste has been disposed in the VLJ-repository in Olkiluoto.
Spent nuclear fuel is stored in an interim store at Olkiluoto. By the end of the year 2000, 853 tons of spent uranium has accumulated at Olkiluoto.
The company's liability for its nuclear waste management was settled by the Ministry of Trade and Industry at EUR 663.0 million at the end of year 2000. The reserve in the Finnish State Nuclear Waste Management Fund, as determined from the liability, is EUR 656.2 million.
In May 1999, Posiva Oy, a company jointly owned by TVO and Fortum Power and Heat Oy, submitted to the Council of State an application for a Decision in Principle for a spent fuel final disposal plant to be constructed at Olkiluoto. In December 2000, the Council of State gave a positive decision. The Finnish Parliament approved the Decision in Principle for the final disposal plant after voting in May 2001.
In November 2000, TVO submitted to the Ministry of Trade and Industry an application for a Decision in Principle for the fifth nuclear reactor unit to be constructed either in Olkiluoto or in Loviisa. The application has been reviewed by all stakeholders, and the respective statements have been submitted to the Ministry of Trade and Industry that prepares the issue for a Council of State decision.
OL1 and OL2 have been in operation for over 20 years. The performance indicators have been favourable. For instance, the average capacity factor for the last ten years is well above 90%.
Already before modernisation the plant design was reasonably modern due to the following advanced features included in the original design:
Numerous design modifications have been implemented since the commissioning of the units. For instance, the containments were back fitted against severe accidents at the end of the 80's. TVO's policy has been to keep the plant continuously up-to-date.
It would be imprudent to take favourable performance for granted. Therefore, TVO started pro-actively a modernisation program in 1994. It was recognised that there were many modifications to be implemented in the next years and a decision was made to include them in a program called "modernisation".
The operating licences of Olkiluoto 1 and Olkiluoto 2 were renewed in 1998. The time schedule of the modernisation was established so that the outcome of the program could be utilised in the operating licence renewal.
From the beginning, the following principles were followed in the program:
The main goals of the modernisation were as follows:
The goals supported each other. For instance, it is easier to license the reactor uprating if safety is simultaneously enhanced. On the other hand, the cost of safety improvements can be compensated for by the additional output working for lower production cost.
In order to achieve the safety goal, the existing plant design has been reviewed and compared to the present and foreseeable safety requirements. The most important requirements are included in the YVL Guides issued by the Finnish regulatory body (STUK) for new nuclear power plants. Compliance with the European Utility Requirements (EUR) has also been reviewed.
The need to fulfil new requirements set for the new nuclear power plants has been considered case by case. The living PSA model of the plant has been utilised within this context.
The most important safety related modifications included in the modernisation program are listed below:
The modernisation program as a whole reduced the severe core damage frequency estimate by a factor of seven.
The radiation exposure of the population was reduced in accordance with the ALARA principle. Liquid releases have been reduced by a factor of ten by improving the liquid waste handling systems. Also occupational doses have been reduced. In practice, this means minimising the cobalt content in the primary circuit.
Four ways were followed to increase the electricity production:
There has not been many operational disturbances until now, but there will be more due to the ageing of equipment and components. Replacement of the components helps in itself. In addition to that, favourable system solutions have been realised that, tolerate more component failures without an adverse impact on the plant operation. For instance the original one out of two turbine protection and control systems have been replaced by a new two out of three system.
Olkiluoto outages have not been very long in the past. However, there is still room for improvement. For instance, the refuelling machine has been speeded up by modernising its instrumentation.
The low pressure turbines have been replaced and in that way about 30 MWe additional production capacity in each unit has been achieved.
The following facts made power uprating possible:
The most important development in this respect has taken place in fuel technology. The operation was started with 8×8 bundles and now 10×10 bundles are used. The new bundles are able to produce 40 percent more power than the old ones.
The reactor uprating is a sensitive matter that must be treated with extreme care. The following criteria have been applied:
The thermal power was uprated from 2160 MW to 2500 MW (15.7 percent). Some design changes implemented due to the uprating are listed below:
The modernisation program continues TVO's policy to maintain and enhance the expertise of the own staff by having challenging projects always in progress. The most important projects since the plant commissioning have been the previous reactor uprating, severe accident mitigation, training simulator, PSA, interim storage for spent fuel, final repository for reactor waste, investigation program for disposal of spent fuel, preparation of the specifications and evaluation of the bids for a new nuclear power plant in the beginning of the 1990's and again in the beginning of the 2000's. All the drive and expertise focusing on a new plant has been directed to the existing plant units.
The modernisation program consisted of about 40 separate projects. The installations were performed during the refuelling outages of the years 1996-1998. In spite of large modifications the refuelling outage times were reasonable, between 15 and 20 days. The test program was quite the same as in the case of a new plant. In addition, the capacity factors of the power plant units have been satisfactory (well above 90%) during and after the modernisation
The total cost of the modernisation program was FIM 800 million.
Licensing steps related to the modernisation program were as follows:
The modernisation program of the Olkiluoto plant was started in 1994 and completed in 1998. Some latter installations were realised during outages in 1999. The modernisation consisted of about 40 projects. The total cost of the program was FIM 800 million. The results were
The provisions for severe accident management were installed in OL1 and OL2 during the SAM project which was finished in 1989. The measures implemented were
Subsequent accident management activities at Olkiluoto plant comprise both the development of accident management procedures and additional plant modifications. They were initiated mainly during the OL1 and OL2 modernisation project. Some hardware changes have been implemented, others are planned. The necessary analyses are often carried out in co-operation with appropriate research institutions.
Emergency Operating Procedures for Severe Accidents have been modified in order to take into account plant modifications and to enhance severe accident management. The containment filtered venting system rupture disk line from the upper drywell will no more be closed in the beginning of an accident. This is a precaution for a possible rapid pressurisation of the containment if the generation of non-condensable gases is large. The previously manual depressurisation of the primary system in severe accidents has been replaced by an automatic actuation of the depressurisation system.
In a severe accident, a large amount of chlorine could be released, due to irradiation and heating, from the synthetic rubbers used as the insulation material of the electrical cables. In order to maintain the iodine retention capability, the sodium thiosulfate concentration of the filter was increased in 1999. The iodine retention capability and stability of the solution have been experimentally verified by TVO and the Technical Research Centre of Finland, VTT.
A large amount of chlorine, which could be converted to HCl in the containment, could reduce the pH of the water pools and wet surfaces. The chlorine originates from the synthetic rubbers used as insulation in cables. This could lead to a significant amount of elemental as well as organic iodine. Another source of organic iodine could be reactions between boron carbide in control rods, steam and iodine in the degrading core.
TVO has investigated the possibilities to enhance the retention of iodine by a containment pH control system. The solution used would be 50% NaOH, which is already normally used by the water treatment plant. A new NaOH tank has been installed. The required NaOH volume was analysed by VTT. The required volume is about 5 m3 according to the calculations. The solution is gravity driven into a raw water storage tank near fire water outlet nozzles, from where the solution is delivered into the containment during containment water filling.
The lower drywell will be flooded from the wetwell prior to the NaOH supply and the lower drywell water pool pH will be kept above 7. The system modifications were made in 2001.
VTT Chemical Technology investigates possibilities to improve the retention of organic iodide. The purpose is to find means to improve the existing containment venting filters so that they are capable of trapping the organic iodine compounds and of preventing iodine from forming organic compounds. Possible means are the oxidation of elemental iodine by modifying the chemical composition of the filter or by using catalytic oxidation. The work started with a literature study followed by experiments. The experiments will be finished in 2001.
TVO has investigated the response of concrete structures in the containment to energetic fuel coolant interactions, steam explosions, and the result is that they would withstand large steam explosion loads. Further studies will deal with the impact of possible steam explosions on the pipe penetrations and personnel access hatch in the lower drywell. The key issue is maintaining the containment leaktightness in severe accidents.
TVO has decided to strengthen the lower drywell personnel access lock. The modifications will be made in 2001 and 2002.
TVO investigates how the diaphragm floor seal would behave in severe accidents. The leaktightness of the seal is important in order to maintain the pressure suppression function of the containment as long as possible.
The piping part inside the lower drywell may be damaged because of contact with core debris. In order to ensure the isolation function in severe accidents, an additional second isolation valve was installed in 1998 in the nitrogen system piping lines from the lower drywell to the reactor building.
During a severe accident, hydrogen gas leaking from the containment might lead to combustible hydrogen concentration in the reactor building compartments. TVO is investigating possible hydrogen combustion loads in the reactor building, including hydrogen burns and detonations. The investigations have started with the preparation of a CFD model of the reactor building to find out the hydrogen transport routes and hydrogen concentration distribution in the reactor building. Hydrogen detonation studies have been performed. An analysis of structural response will be finished by 2002. The concern is that containment penetrations might be damaged due to hydrogen combustion phenomena outside the containment which could lead to a large leak.
To secure depressurisation of the reactor primary system in severe accident situations and to prevent a new pressurisation of the reactor, two valves of the relief system have been modified. It is now possible to keep the valves open with the help of nitrogen supply or water supply from outside the containment. The modification was finished in 1999.
The SIRM detectors will be drawn in the beginning of the accident half a meter below the active core to detect possible recriticality. Analyses were performed in 1999 to determine how to relate the reading of the SIRM monitors to actual reactor power.
The two utilities (TVO and Fortum Power and Heat Oy), the major Finnish inspection companies and VTT established a working group (nowadays steering committee) to outline a Finnish qualification system considering national objectives, purposes and situation. The principle was that no new qualification organisation should be established for these activities in Finland. The available resources and organisation should be integrated into the qualification system for inservice inspection in Finnish nuclear power plants. The document "The qualification of inservice inspections" outlines the principles followed in Finland in the qualification of pre- and inservice inspections of nuclear power plant components. The document is a living document and will be updated with experiences gained from first inspection qualifications. The document fulfils the recommendations of European methodology for qualification of non-destructive tests, second issue (ENIQ) 15.1.1997.
The utility has an overall responsibility for the performance of the inservice inspections. The steering committee is nominated by the utilities. For each qualification task the steering committee nominates and establishes a qualification body on the initiative of the utility. The steering committee receives an order from the utility for the qualification of an inspection, or a part of it.
The steering committee has an important role in inspection qualification. The main tasks of the steering committee are:
The members of the qualification body are level 3 experts on a specific inspection technique. One is a representative of the Finnish National Qualification Body and, if needed, the others are experts from utilities or research institutes. The level 3 members or the expert members of the qualification body, usually from Finnish inspection vendors or utilities, must be independent in relation to the organisation that is taking part in the qualification.
The representative of the Finnish National Qualification Body, who is completely independent, informs and reports directly to STUK about the work of the qualification body. The main activities of the qualification body are:
The utility has the overall responsibility for the performance of the inservice inspections and also for the verification of the efficiency of inspections. The utility is also responsible for applying for the acceptance of different tasks from STUK. The inspection items for which qualification will be carried out are proposed by the utility. All input data necessary for the qualification will be submitted to the qualification body and to the inspection vendor by the utility.
The utility is also responsible for the preparation of the inspection procedure and the technical justification used in qualification. Normally these documents are prepared by the inspection vendor.
The utility is responsible for the procurement of the test specimen needed in the practical tests as well as for the reservation of the facilities and resources necessary for the performance of qualification.
The first totally qualified inservice inspection documents have been submitted to STUK for approval as a pilot project.
TVO's operating experience feedback group consists of 6 members and 3 advisors. This onsite group gives recommendations to the line organisation that makes decisions on eventual corrective actions. The industry operating experience from similar reactor types is followed by several means. The main sources of information are ERFATOM, KSU, WANO and Forsmark. These are explained in more detail below. Information is also coming directly from several sources (IAEA and OECD/NEA (IRS), Loviisa power plant (e.g. operating experience meetings and reports), vendors (Westinhouse Atom, Alstom Power Sweden AB), component manufacturers, the WANO Network, BWROG (BWR Owners Group).
ERFATOM was founded by the Swedish utilities and TVO as a consequence of the so called Barsebäck incident (July 1992). Activities started on January 1st, 1994 in the premises of former ABB Atom (Västerås, Sweden). Nowadays ERFATOM is part of the NOG (Nordic Owners Group) and issues reports every two weeks and topical reports when needed. ERFATOM also gives recommendations. ERFATOM co-operates very closely with KSU (Swedish nuclear training and safety center). KSU concentrates on operational safety issues and they have the responsibility to screen out external (international) operating events. ERFATOM screens out internal events from Swedish Nuclear Power Plants and from Olkiluoto.
TVO is a member of WANO (World Association of Nuclear Operators). Although KSU screens out important events reported through the WANO Network, TVO reviews independently all the SOERs (Significant Operating Experience Reports) and SERs (Significant Event Reports) reported by WANO. Forsmark units 1 and 2 in Sweden can be called as "sister units" of OL1 and OL2. Reports from Forsmark 1 and 2 (e.g. licensee event reports) and minutes of the meetings of the Forsmark safety committee are reviewed regularly.
In addition to the above, TVO participates actively in WANO programs and in several international technical groups (such as valve group, reactor group and turbine group) which have regular meetings about twice a year.
The modification handling procedure in Olkiluoto has been under continuous development since the early 1980's.
After the modernisation program and several reviews of TVO's working methods, experiences have been collected in a separate development project. The project was realised during the years 1997-1999 and it had participants from operation, maintenance, quality assurance, safety, modification planning and refuelling planning. Special attention was placed also on the new modern automation and on modifications during the field installation phase.
The project started with exploring
On the basis of the results of the above mentioned studies and other experiences, about 60 remarks on the state of the modification process were collected to be taken into account in the development work. The target state was defined and it was also checked that all remarks had been taken into account. In addition, many new ideas were found by the project group itself.
In the development work, detailed procedures were defined making the decision process more exact and taking into account the opinions of all parties in TVO´s organisation. Some of the most significant modifications made included:
The practice has shown that there is still need for continuous improvement to keep the personnel motivated and to take into account all aspects to guarantee safe and reliable long term operation of the power plant.
General training, discussion and development seminars have been arranged to continue the modification process development and to get the working organisation committed to the new procedure.
TVO has developed and re-structured the quality assurance program for operation during the past three years.
The main objectives for the development of the quality assurance program have been:
During the development work on the quality management system, the requirements from the following documents have been taken into account:
As a result of the development work, TVO has established a new quality management system the description of which has been published as a quality management manual, internally called Performance Manual (Toimintakäsikirja).
The present Quality Assurance Manual of operation has been the Quality assurance program of the licensee accepted by STUK on the basis of Guide YVL 1.9 Quality Assurance during Operation of Nuclear Power Plants. TVO has published the internally accepted quality management system at the beginning of the year 2001. The requirements of the present Quality Assurance Manual of operation are still valid.
TVO has delivered to STUK for approval a plan for the replacement of the present Quality Assurance Manual with a new Quality management system.
TVO has delivered to STUK for approval a general description of the new quality management documents needed on the bases of Guide YVL 1.9 Quality Assurance during Operation of Nuclear Power Plants. After approval by STUK the new quality management system will replace the present Quality Assurance Manual as the operational Quality assurance program of the licensee.