Over Eleven Years of Cernavoda NPP Good Operation Performance - Highlights

Transcription

1 Over Eleven Years of Cernavoda NPP Good Operation Performance - Highlights Mihai Victor CASOTA Counsellor at Investments & Technical Support Department of S.N.NUCLEARELECTRICA, Bucharest, ROMANIA ABSTRACT This paper provides highlights of the Romanian Nuclear Program evolution since its beginning up to now. The paper presents the evolution and general description of Romanian Nuclear Power Sector organization, especially of the Romanian nuclear power company Societatea Nationala Nuclearelectrica S.A., short description of the Cernavoda NPP, units design characteristics, main milestones achievements in Cernavoda NPP construction and commissioning, status of the Cernavoda NPP Units, evolution of the Performance indicators of Cernavoda NPP in commercial operation and main major Operation problems that Cernavoda NPP faced them. 1. EVOLUTION AND DESCRIPTION OF ROMANIAN NUCLEAR PROGRAM There are three distinct phases in the evolution of the Romanian Nuclear Program. The first one beginning phase is that before Romania opted for the CANDU system in mid 60 s and this option proved, on long term, to be an excellent choice that was beneficial for his National Nuclear Power Program. At that time, the main reasons for this choice of the Romanian authorities were related to the nuclear safety issues, the outstanding performance demonstrated by the CANDU type reactors and especially related to the strategic advantage of the CANDU system that the nuclear fuel can be supplied locally. The first Nuclear Power Plant in Romania was designed to operate with 5 units, CANDU-6 type, with a Generated Power of MW(e) each. The site was chosen in SE of Romania, on Danube River, close to Cernavoda town, about 180 km far away east from Bucharest. The Cernavoda Nuclear Power Plant Project started in In the 80 s the Governmental program for nuclear energy was quite impressive and too ambitious, in some aspects even unrealistic. It has included the heavy water and nuclear fuel fabrication for all five CANDU-6 reactors to be constructed at Cernavoda. As it is well known, the heavy water and nuclear fuel manufacturing technologies were developed before 1990 without any Canadian support, and reached an impressive level. However, the political ambitions of the former Romanian authorities to involve the national potential in a too big and unrealistic scale undermined the progress of Romanian Nuclear Power Program. This has resulted in considerable delays in the Nuclear Power Program as well as significant economical losses. The second phase transition phase was that between 1990 and mid The Cernavoda Project was run under direction of several Ministries from its initial stages, back in 1979 until

2 when Romanian Electricity Authority (RENEL) was created under direction of Ministry of Industry, and was charged by its division Nuclear Power Group (GEN) with construction, commissioning and operation of Cernavoda NPP. The Nuclear Power Group included Cernavoda NPP and the entities performing support activities (production of nuclear fuel and heavy water, engineering and research). On august 1991 RENEL signed a contract with a Consortium (AAC) formed by AECL Canada and ANSALDO Italy. The main scope of this contract was the provision of all resources, services, equipment, tools, materials and supplies required for the completion of the Unit 1, the management and control of all work associated with the Unit 1, including operating the unit for a period of 18 months. In the new political climate installed after 1990, the nuclear policy was significantly modified. The clear objective became the development of a reliable, efficient and realistically dimensioned national nuclear industry, by combining the already significant existing local potential with the benefits of an open and concrete co-operation with our foreign partners, essentially from Canada. A solid frame for a real and consistent co-operation was put in place. The third phase maturity phase started in July 1998, when RENEL was restructured. According to the restructuring strategy of the power sector in Romania the former Nuclear Power Group was separated of RENEL and split into two new entities, both reporting to the Ministry of Industry and Trade: Regia Autonoma pentru Activitati Nucleare (RAAN),an autonomous authority for nuclear activities, with head-office in Turnu Severin, in charge with heavy water manufacturing in Turnu Severin, Engineering for Nuclear Objectives in Bucharest and Nuclear Research in Pitesti; Societatea Nationala Nuclearelectrica (SNN S.A.), a joint-stock company having 3 branches, with its head-office in Bucharest, responsible for the production and supply of energy from Cernavoda NPP, as well as for its development, and for nuclear fuel manufacturing at Pitesti Fuel Plant. The National Commission for Nuclear Activities Control (CNCAN) is the governmental Regulatory Body, responsible for full surveillance and control in all areas relevant to nuclear safety and environmental protection in the sitting, construction, commissioning, operations of the nuclear plants, research reactors and other nuclear facilities in Romania. The Romanian Nuclear Program was also complemented with major organizations for engineering, manufacturing and erection for systems and components, and with the supporting educational infrastructure. There have passed over 29 years since the nuclear power plant s construction works started on the Cernavoda site. It was a beginning, so far back in the past, which some people met with enthusiasm while others with scepticism. Who was right? At that time back in 1979, the works schedule stipulated that Unit 1 would be commissioned in 1985.The event only occurred in 1996!. The overall progress of construction work was very slow, due to various economical and political factors. But so many events happened in Romania and all over the world between 1979 and 1996 that the work completion, even behind time, can be considered a great success. Some moments and turns of life have put a mark on the above mentioned period and had negative repercussions on the Cernavoda works progress. On the other hand, some circumstances have contributed towards the success of works completion. Even more could be said about each of these aspects, but they are already history; they just help us better understand the Cernavoda NPP s history.

3 SOCIETATEA NATIONALA NUCLEARELECTRICA PRESENTATION In July 2008 Societatea Nationala NUCLEARELECTRICA (SNN SA) has celebrated 10 years since it was set up. NUCLEARELECTRICA is a joint-stock company reporting to the Ministry of Economy and Finance. The Romanian state is the major shareholder while the rest of the shares are held by the Property Fund. His main mission is the production of nuclear generated electricity power and supplying the thermal power necessary for the Cernavoda town district heating and for the industrial heating needs of the Cernavoda NPP site. Another mission is the manufacturing of CANDU 6 type nuclear fuel. The Head Office is located in Bucharest and, coordinates the activities of its branches: Cernavoda Nuclear Power Plant Branch Sucursala CNE-PROD Cernavoda that safely operates Units 1&2 and provides hot water to the Cernavoda community for district heating; Pitesti Nuclear Fuel Plant Branch Sucursala FCN Pitesti, qualified manufacturer for CANDU 6 type nuclear fuel that fully covers the needs for the operation of two units. The company, through its Head office, is in charge of caring out business activities on the electricity market, developing complementary projects and is also involved, as the main investor and promoter in the establishment of the Project Company that will be responsible for the completion and commissioning of the Cernavoda NPP units 3&4. Cernavoda NPP is responsible for the operation of Units 1 & 2 ensuring high safety, economic efficiency and taking care of people and the environment, training of the personnel qualified to deal with plant s specific procedures in accordance with the safety culture concept. Unit 1 began its commercial operation on December 2, 1996 followed by Unit 2 on November 1, The Nuclear Fuel Plant in Pitesti is a qualified manufacturer of CANDU 6 type nuclear fuel bundles (It is certified by AECL Canada and Zircatec Precision Industries). The plant completed the process of doubling the production capacity in 2007 and is able to ensure the fuel quantity necessary for the operation of the two units of the Cernavoda NPP. 2.1 Cernavoda NPP Design characteristics of the Cernavoda NPP units The Nuclear Steam Plant is based on a CANDU PHWR type reactor, designed by Atomic Energy of Canada Ltd. (AECL), similar to those operating in Canada, Korea, Argentina and China. The Balance of the Plant is based on a General Electric (USA) turbogenerator of MW(e); the thermal cycle and the electrical systems were designed and supplied by Ansaldo - Italy. CANDU PHWR reactor is a Pressurized Heavy Water Reactor, with 380 horizontal fuel channels. The fuel used is natural Uranium dioxide. The refuelling is performed on-load. The cooling agent is heavy water at a pressure of 9.9 MPa. The moderator is, also, heavy water, but in a separate system, at low pressure and temperature. The CANDU reactor "burns" natural uranium fuel, using heavy water of nuclear grade (with an isotopic content higher than 99.75% D 2 O) as moderator and coolant, in two independent closed systems [1]. The layout of the main and auxiliary systems is represented in the figure 1. The heat transport system circulates pressurized D 2 O coolant through the fuel channels to remove the heat produced as a result of the nuclear fission of the uranium. The primary

4 coolant transports, by the four main primary pumps, the heat to the four steam generators where it is transferred to the feed water (secondary coolant) to produce saturated steam. The Nuclear Steam Supply System of the unit is installed in Containment, aimed to confine the radioactivity, released from the process systems in the case of an accident. Figure 1 CANDU-6 NPP Layout of the main and auxiliary systems The saturated steam enters the high pressure turbine. By its expansion, the steam rotates the turbine; in the electrical generator, the mechanical energy of the turbine is converted into electricity. After getting out of the turbine, the steam condenses into the turbine condenser, as the resulting heat is removed by the cooling water from the Danube River. The water is then returned to the steam generators via the feed water heating system. The main design data of the Cernavoda NPP units are presented in the table 1. Table 1: Units technical design characteristics Thermal power MW(t) 2064 Gross installed capacity MW(e) Auxiliaries consumption % < 8 Fuel channels number Loops number - 2 Main primary pumps - 4 Steam Generators number - 4 (D 2 O) pressure inside the primary circuit MPa 9.9 Temperature outside the primary circuit C 310 (H 2 O) pressure saturated steam MPa 4.8 Supply water temperature C The reference design for Unit 2 is the as built Unit 1, with a certain number of improvements. A number of changes (133) were aimed to meet the new regulation by providing increase in the margin of safety or to improve the reliability of operation in accordance with the development of the nuclear technology. Other changes (about 170), of minor character, have improved system or station performance, or have replaced the obsolete

5 equipment. The design changes were mainly based on the experience acquired in the construction and operation of other CANDU 6 units[1] Construction Facility for Intermediate Dry Storage of the Spent Fuel Now on Cernavoda site another project is being implemented: the construction of the interim dry storage for the spent fuel. The contract for this project was signed on April 6 th, 2001, between Nuclearelectrica and Atomic Energy of Canada Ltd. It is a turn-key contract, providing the engineering transfer and the construction of the first two modules of the storage. The reference project is that used at Gentilly NPP, in Canada. A storage module (MACSTOR -200 type) consists of a monolithic structure (vault) made of reinforced concrete; it contains 20 metallic storage cylinders, for a total capacity of bundles per module. The cylinders are cooled by air convection. The first three modules are available since 2003 [1]. The final capacity of the storage, corresponding to 40 operation years of 4 units, will be of 4 modules MACSTOR-200 and another 34 will be MACSTOR-400 type, of double capacity Training Centre A large and modern training centre was built close to the station, and became available for the plant s personnel training in The centre has a full-scope simulator, supplied by CAE-Canada. The simulator was adjusted to replicate entirely the Unit 1 of Cernavoda NPP. If the first crews of the operating personnel learned their jobs in Canada, at Point Lepreau NPP, now the training of the new personnel, the refreshment training and the special courses for the personnel who has to be licensed by the Regulatory Body take place in this centre. A challenging task for all the company, but especially for the training centre, was the recruitment and training of the operating personnel for Unit 2 of the station. In the future, we expect that will be also opportunities for the centre to train the operating staff of other CANDU worldwide projects, when such needs will appear Prospective: Units 3 and 4 Romanian Government approved in 2007 the strategy to attract investors for the completion of Units 3 and 4 of Cernavoda NPP, including the schedule for the establishment of a new entity, a Project Company, to be charged with completion of this project. The Units 3 and 4 are designed as CANDU 6 units, of 706 MW (gross) capacities, similar to Unit 1. The civil work (Reactor and Turbine buildings) of these units are mostly completed, but unlike the Unit 2, the main equipment is not procured. According to the country s energy strategy, the Units 3 and 4 of Cernavoda NPP should be in service by the end of It is estimated a part of the energy produced by these units will be exported Local Community Support The plant s construction brought on a Special social program for the improvement of living standard in Cernavoda town, inaugurated in A new hospital, a high school, new blocks of flats and stores, roads, running water and district heating supply grids, etc. were built in Cernavoda. New buildings will be erected for the personnel working for the construction and, afterwards, for the operation of Unit 3&4.

6 PERFORMANCE OF CERNAVODA NPP DURING COMMERCIAL OPERATION During over eleven years of commercial operation, the contribution of Cernavoda NPP to the energy production in Romania was notably steady: every year, the nuclear unit delivered to the grid around 5 TWh for the unit 1, representing about 10% of the electricity output in the country and since 2007 around 9.67 TWh for two units, representing 18 %. The Unit 1 produces and supplies, also, heat for the station s construction site and for the district heating of the town, representing an output of about 50,000 Gcal/year. Due to the reactor s capacity, the unit is able to supply heat from live steam, without diminishing the electrical capacity below the rated value. The Load Factor of the Unit 1 since in service is %, value which places it on the fifth position in the Ten Top of CANDU 6 units. The best performance was achieved in Over the year 2007 the Unit 1 generated an amount of electricity of 6.96 TWh, out of which 5.18 TWh were supplied to the national power grid. On September 21, 2007, the Unit 1 registered 350 days of continuous operation. The Load Factor of the Unit 1 in 2007 was %, the best achievement ever reached by this unit. The Load Factor exceeded the value of 90 % for the last three years in a row. On August 7, 2007, during the commissioning tests, the Unit 2 was connected to the grid and on September 26, 2007 began to operate at full power and from November 1, 2007 began its commercial operation Operation performance indicators For the assessment of the operation activity at Cernavoda NPP we present below some performance indicators. According to the Power Reactor Information System (PRIS Data) IAEA [3], the overall production performance is described primarily by the indicator Load Factor. It is the ratio of actual energy generation (net) to reference energy generation over a certain period of time [3]. You can see in the figure 2 the evolution of Load Factor during commercial operation of Cernavoda NPP U U U1 Lifetime GCF 87,27 86,19 84,51 88,3 88,25 89,37 79,52 89,71 90,08 91,37 97,62 93,23 88,44 Figure 2: Unit Gross Capacity Factor Evolution Another indicator which reflect the overall production performance is Unit Capability Factor (UCF). It is the percentage of maximum capacity generation that a plant is capable of supplying to the electrical grid, limited only by factors within control of plant management.

7 Table 2: Performance indicators of Cernavoda NPP Unit 1 Year UCF UCLF EAF The UCF values recorded at Cernavoda NPP Unit 1 for were in the range of % while the Median World by type PHWR values were in the range of % [4] The values for the indicator Unplanned Capability Loss Factor - UCLF (which expresses the energy lossses caused by the unplanned shutdowns and unplanned extentions of outages) were in the range of 0,33 9,64%, while the Median World by type PHWR values were in the range of % [4] The values for the indicator Energy Availability Factor (which expresses percentage of maximum capacity generation of a plant that is available for supplying to the electrical grid, limited only by all factors) were in the range of %, while the Median World by type PHWR values were in the range of % [4]. The units were operated in accordance with all the applicable requirements of nuclear safety and radioprotection. The average individual dose received by the station personnel was 1.38 msv/year, while the legal allowable individual limit is 20 msv/year. The maximum value of the collective radiation exposure was man*sv in 2003, versus CANDU-6 mean value of man*sv. The radioactive emission to the environment, expressed as the equivalent dose to critical group of population resulting from that emission, was 7.81 µsv/year (the dose from the natural background is µsv/year).the maximum value of volume of the radioactive solid waste produced by Cernavoda Unit 1 was m 3 in 2004 [1]. The high results in the electricity production at Cernavoda NPP Unit 1 were possible due, also, to the excellent quality of the nuclear fuel manufactured in Pitesti at the Nuclear Fuel Factory. The number of failures of the fuel was very small; during five consecutive years no failure was recorded on the fuel bundles loaded from the reactor core [1] Some major Operation problems that Cernavoda NPP faced them During eleven years of commercial operation, we already accumulated a large experience in carrying-out the annual outages at Cernavoda NPP. It is worth mentioning the baseline (inaugural) inspection of the reactor s fuel channels, performed with the assistance and using the special tool supplied by AECL. All the turbine cylinders and the electrical generator have been opened and inspected, with the assistance of the supplier General Electric USA; also, some repairs to the turbo-generator were performed. Another special operation consisted in the inspection of the Steam Generators, carried out by Siemens specialists. As in every plant, some unplanned outages took place at Cernavoda NPP, too. These events had very diversified causes, from spurious signals to equipment failures. The failures that occurred were not essential and did not alter the main equipment; as a rule, such failures were quickly fixed and the unit restarted, as soon as the reactor poisoning decreased to the requisite level. These outages were not significant from the safety point of view and had no radiological effects on the population and environment. The unplanned outages, as operational events, are assessed according to a dedicate procedure, in order to understand the root-causes of the event, to define the necessary corrective actions and to prevent their recurrence. The conclusions of these assessments are disseminated among the interested

8 station s personnel as well as to the twin units worldwide - in the framework of the Operational experience program. In 2003, the seventh year of commercial operation, Unit 1 Load Factor reached the lowest value: 79.52%. This thing was possible because of two major events: A very complex annual planned outage (including the rewinding of the electrical generator field), carried-out successfully, in a reasonable compliance with the schedule; The shut down of the unit because of the drought and extremely low level of Danube, which threatened the normal operation of the condenser cooling pumps; the unit remained shut-down for 27 days. During the planned outage, some important and complex maintenance operations and repairs were performed, such as: the repair of the electrical generator, the second in service inspection of the reactor s fuel channels, the Reactor Building Leak Rate tests. The outage was completed in 47 days, with an extension of 1, 5 day only versus the initial schedule [2]. We point out that, in spite of the lowest value of Load Factor achieved, Unit 1 experienced in 2003 only one unplanned outage due to a failure, lasted no more than 4 hours Conclusions After over eleven and half years of commercial operation of Cernavoda NPP, we can say for sure that our company Nuclearelectrica had a very impressive evolution with an ascendant trend of the performance. The findings of the IAEA OSART and WANO Missions and their Follow-up s which took place at the Cernavoda NPP during this period have proved it. The recommendations and suggestions received on these occasions have allowed us to check out the performance level we have reached, to identify the areas that need improvement and the necessary improvement and the means of implementation. The very good performance gave us the recognition of our company as a factor of economic stability, highly contributing to the development of tomorrow's world. The efforts of our staff received significant support from the international nuclear community and organizations. We proved our capability to work with specialized international organizations. The Nuclear Operators have not only the individual responsibility for the safety of their own plants, but they have to take the joint responsibility for continuously increasing the safety level of the nuclear power plants all over the world! 4. REFERENCES [1] Dumitru Dina, Mircea Metes, Mihai Casota, Present and Future at Cernavoda NPP, Energia nucleara magazine, Bucuresti, [2] Mircea Meteş, Mihai Caşotă, Some Topics on the Operation of Cernavoda NPP, Energia nucleara magazine, Bucuresti, [3] IAEA, The Power Reactor Information System (PRIS) and its extension, Technical Reports Series no. 428, Vienna, 2005 [4] IAEA PRIS-Nuclear Power Plant Info