Temelin 1000 MW Units Active Testing Stage - Commissioning Experience

Transcription

1 International Conference Nuclear Energy for New Europe 2003 Portorož, Slovenia, September 8-11, ABSTRACT Temelin 1000 MW Units Active Testing Stage - Commissioning Experience Ing. Olga Ubrá, DrSc., Ing. Vladimír Říha, MBA Škoda Praha, a.s. Milady Horákové 109, Praha 6, Czech Republic dtsp36@temelin.skodanet.cz There were three basic stages of the NPP Temelin Units active testing stage- The zero and low power testing, The power ascension testing and Plant Performance Test. The main objective of the start- up process stages and the testing procedures including some operational experience are described in the paper. 2 INTRODUCTION Temelin Nuclear Power Plant (NPP) is located in southern part of the Czech Republic about 130 km from Prague and 60 km from the Austrian border. The NPP Temelin is equipped with two VVER 1000 reactors, each with thermal output of 3000 MWt and two turbogenerator sets with electrical output 2x 1000 MW. The project investor is Czech Power Company ČEZ, the general supplier for the mechanical and electrical equipment was ŠKODA PRAHA Company. The VVER 1000 represents the third generation of pressurized water reactors developed in the former Soviet Union. The primary system is of a four-loop design. Each loop of the reactor coolant system includes a horizontal steam generator and a vertical centrifugal single- stage reactor coolant pump. The operating pressure is 15.7 MPa at temperature 280/ 310 o C. The electrical output of a turbogenerator set is 1000 MWe. The saturated steam turbine 1000 MW, 3000 rev/min is of ŠKODA design. It includes one high- pressure and three low- pressure cylinders and between them two horizontal moisture separators and reheaters are located. The three condensers are equipped with Titanium tubes. The bypass system accepts 60% of full load steam output. Cooling of condensers is assured by the cooling tower circuit with 4 natural air draft cooling towers. The decision for construction of 4 units, type VVER 1000 in the Temelin location was made in In the year 1984, a contract for the supply of the Russian Technical project was concluded. This project included the primary system, auxiliary service building and diesel generator station. The initial project of the secondary system and other parts of the NPP were processed by the Czech general designer Energoproject in The construction permit was issued in In the year 1990, the requirement of electrical output was revised and it was decided to complete only two 1000 MW units and substantially upgrade the design and the operational safety and flexibility of the NPP Temelin. The original project was already being improved by the Czech experts prior to Hundreds of individual improvements were implemented. Certain measures were taken in order to ensure compliance with the ISO 9000 standards in the field of components and construction. Approximately 90% of the components of the primary system and 100% of the components of the secondary system were manufactured in Czech Republic or in western countries

2 406.2 In the course of the years 1990 to 1992, international audits and expertise and IAEA mission were carried out at the NPP Temelin. Based on the conclusion of IAEA mission, Halliburton NUS audit and the other expertise and in compliance with recommendation of the Czech nuclear regulatory body and of the Czech experts a modernization program for NPP Temelin has been carried out. The following innovations have been implemented: Modernization and upgrading of the safety and control systems, Fuel replacement and modification of the reactor core, Innovations of some components and subsystems of the primary and the secondary systems, replacement of the original cables with ones of higher fire rating, Design and construction of a full scope simulator, The improvement of safety documentation, elaboration of the Probabilistic Safety Assessment. The tenders for instrumentation and control system, nuclear fuel, diagnostic system and radiation monitoring system were issued to the world-well known suppliers. The US Company Westinghouse Electric Corporation was selected to submit contract for the delivery of instrumentation and control system, primary side diagnostic system and for the delivery of nuclear fuel. The contract for the delivery of instrumentation and control system was signed in 1993 and the contract for the delivery of fuel including safety analyses was signed in Since 1995 after the completion of revisions and adjustment work and the finalization of assembly, the preparation on NPP commissioning began. There were 3 main stages of the NPP Temelin commissioning: Preparatory stage (individual tests of assembly and a first part of extended hydrotest) Non-active testing stage (a second part of extended hydrotest and REVISION) Active testing stage (zero and low power testing, power ascension testing and plant performance test) In 1999, all efforts of contractors were focused on the preparation of the first stage of extended hydrotest, which began on Unit 1 in October 1999 and on Unit 2 in July The purpose of the first stage of the extended hydrotest was to verify the tightness of the equipment and the primary circuit piping at a pressure 17.6 MPa and 24.5 MPa. More than 3000 individual tests were provided on the Unit 1 and 1576 tests on the Unit 2 from the start of testing to the end of the first stage of the extended hydrotest. In February 2000 a non- active testing stage on the Temelin NPP Unit 1 began. The second stage of extended hydrotest was completed successfully in April 2000 on the Unit 1 and in November 2001 on the Unit 2. After the second stage of the hydrotest a REVISION (inspection) was performed. During the REVISION all detected defects were fixed and preoperational checks were performed. After the REVISION substage active testing stage began. The first step of this process was transportation of the first container with fresh fuel from the fresh fuel area into Unit containment building. There were three basic stages of the Temelin Units active testing stage: The zero and low power testing Physics start- up tests (procedure of the basic series F) The power ascension testing (procedures of the basic series E) Plant Performance Test 3 TEMELIN ACTIVE TESTING STAGE 3.1 Physics Start-up Tests Physics start-up testing of Temelin NPP Unit 1 began in July 2000 and of Unit 2 in March The main objective of the physics start-up testing was to verify characteristics of the reactor core important for nuclear safety as well as for more accurate determination of

3 406.3 neutron-physical characteristics, which are used in the course of unit operation. Physics start-up tests of Temelin Units were divided in accordance with the approved Program of Physics Start-up Tests F001 into the following three time periods. The first period of the physics start-up tests included: fuel loading and reactor assembling filling-in of the primary circuit by coolant leak-tightness pressure tests of the primary and secondary system. repeated containment integrity test The second period included: heating above the brittle fracture limit temperature heating to semi-hot (Mode 4) and hot (Mode 3) state (280 C) performance of tests required by the operational procedures for reactor start-up repeating some tests performed during Hot Functional Tests The third period included: reaching initial reactor criticality physics start-up tests First stable criticality on the Unit 1 reactor was reached in October 11, 2000 and on the Unit 2 reactor in May 31, The basic physics start-up tests, which started at the moment of the initial criticality were performed at zero or very low reactor power, when fission reaction had not yet heated the primary coolant. In compliance with the Physics start-up test phase program document the following tests were performed: Denotation F001 F002 F003A F003B F003C F003D F004 F005 F006 F007 F008 F009 F010 F011 F013 F014 F015 F016 E008 E010 Name of the test procedure Low power physics test sequence program Initial core loading Initial criticality Determination of physics testing operational range of power Source-term determination Reactivity computer check out Verification of the control rods connection with their drive mechanism Differential and integral control rod groups worth, and boron worth Rod-drop measurement Isothermal temperature reactivity coefficient and pressure reactivity coefficient measurement Incore thermocouples calibration Reactivity power coefficient measurement NIS calibration up to 1.5 % rated thermal power (RTP) Reactor coolant system thermal capacity and heat loss determination Reactor coolant system hydraulic characteristics measurement Core symmetry verification Boron injection system lag measurement determination Reactor neutron noise characteristics measurement Radiation monitoring during physics start-up and power ascension tests Measurements of the equilibrium Xenon worth Based on the results of physics start-up tests it was determined that reactor core of both Temelin Units meets safety and design requirements and the characteristics of the reactor core of both Temelin Units comply within acceptable allowance with predicted results.

4 406.4 Besides basic physical tests several hundreds individual tests of equipment were provided in the course of the period of Physics start-up tests - on the Unit 1 about 1000 individual tests and on the Unit 2 about 600 tests. Based on acceptable results of all tests performed according Program of Physics Start-up Tests it was recommended to proceed into the power ascension test phase. 3.2 Power Ascension Testing Power ascension testing on Temelin Unit 1 began at the end of November 2000 and on the Unit 2 at June The main objective of the power ascension testing was to transfer the Unit from Mode 2 (power level <2% rated thermal power (RTP)) to Mode 1 (power level >2% RTP) and to bring it successfully to the rated plant power. In the course of the process of the gradual power ascension, all basic design functions were tested. The Unit and its major components properties were verified in normal steady state as well as in non-steady state operation modes and in abnormal operation conditions. At the end of the stage, a safe and reliable Unit operation was demonstrated by the 144 hours trial run. A binding scenario of the activities carried out during the power ascension testing was the Program of Power Ascension Tests E001. The process of the power ascension testing, from the transition into the MODE 1 till achieving of the rated power was divided into substages that followed both logically and in time. Power ascension testing of Temelin NPP Unit 1 per the approved program E001 was divided into seven substages which were limited by the reactor power levels 5%, 12%, 30%, 55%, 75%, 90% and 100% of the RTP. The 144 hours Unit trial run was a part of the last substage. The process of the Unit 2 power ascension testing was subdivided into four substages limited by the power level 30%, 55%, 75% and 100%. The performed commissioning and verifying activities were aimed in particular at the following areas: putting the secondary system into full operation including verification of the design functions of the basic components and confirming of the thermal and mechanic properties of the new machine hall equipment as turbogenerator set, reheater and condenser, verification of the unit operation in steady state operation modes at gradually increasing reactor power levels, in particular verification of the parameter stability and of the performance of the process equipment in connection with the control system, verification of the unit operation under abnormal operation conditions and transients initiated by the trip of a major unit components including the verification of the control system performance, demonstration of a reliable and safe unit operation in all other basic unit operational modes, i.e. during the heatup, criticality achieving, power ascension, shutdown, hot standby and during the cooldown. verification of the neutron, thermo-hydraulic and mechanical properties of the reactor core, verification of the performance, reliability and correct setup of all parts of the control system in connection with the process (control circuits, sequences, limitation and protection system), both in normal operation modes conditions and, in particular, from the point of view of mastering abnormal operation conditions and transients without violating the Plant Technical Specifications. The units verification were provided for by the following tests:

5 406.5 in accordance with the test procedures of the basic series E- altogether 39 procedures covering partially or fully the basic areas of the unit verification, i.e. physics and thermohydraulic measurements, calibration, chemistry and health physics measurements, verification of the design functions of the equipment including the control system and verification of normal and abnormal design modes, in accordance with the test procedures of the F series- 3 procedures that continue the activities performed in the course of the zero and low power testing stage, in accordance with the test procedures of the P series - these are in most cases tests of basic process equipment with the medium for which the proper conditions could not be setup before the power ascension stage. In addition to that, those are tests of the electric equipment connected with the power output and tests of secondary diagnostic system, in accordance with the test procedures of the V series - altogether 19 procedures that verify the properties of the new design and new structure elements and components of the secondary circuit. They are, in particular, aimed at the verification of thermal-hydraulic, aerodynamic and mechanical properties of the turbine, reheater and of the condenser. Regarding the test procedures of the E, F, P series, there was only small difference between the first and the second Temelin NPP Units. The test procedures of the V- series were provided on the Unit 1 only, because of new design lot of Unit 1 secondary system components and elements. The Unit 1 turbine is the first 1000 MW saturated steam turbine (prototype) which was designed and manufactured by Škoda Company. The inclusion of the tests into individual substages corresponded with the substages objectives and complied with the requirements specified in the procedures. The short summary of the most important objectives of the NPP Temelin Unit 1 substages follows: The substage up to 5% RTP: 1. Verify the Unit transition from the Mode 2 into the Mode 1 and safe increase of its power to 5% RTP and master normal operation at the given power range. 2. Verify the design functions of the auxiliary condenser, of the steam dump to condenser and of the secondary system components that have been for the first time put into normal operation (the turbine driven feedwater pump, condensate system). 3. Perform calibration of the excore ionization chambers neutron flux measurement instrumentation by the power range and wide range channels. The substage up to 12% RTP: 1. Verify the start of the turbogenerator set to nominal speed and the start up of the related machine hall equipment. 2. Perform primary tests of the turbine alternator, its exciter generator, and its protections. Carry out turbogenerator set counterbalancing (if necessary) 3. Verify the natural primary loop coolant circulation start and demonstrate the unit s ability to remove the design anticipated residual decay heat by means of the natural circulation. 4. Verify the performance and stability of the reactor power control and the steam dump to atmosphere control and master the unit operation at the given power range. The substage up to 30% RTP: 1. Complete the preparation of the turbogenerator set and of terminals to normal operation and synchronize the turbine generator to a 400 kv line. 2. Perform calibration of the excore ionization chambers neutron flux measurement instrumentation and calibration of the incore measurement system at the given power level. Verify neutron characteristics of the reactor core. 3. Determine the steady state Xe poisoning and examine the reactor core power distribution deformation due to incorrect position of a control rod and its influence on the ionization chambers indications. Determine the characteristics of azimuthal Xenon oscillations.

6 Verify the Unit performance at complete black- out and the unit cooldown and start from cold conditions. Master the unit operation at the given power range. The substage up to 55% RTP: 1. Perform calibration of the excore ionization chambers neutron flux measurement system by the power range (PR) and wide range (WR) channels and calibration of the incore measurement system at 55% RTP. 2. Determine the steady state Xe poisoning and verify neutron characteristics of the reactor core. 3. Verify mechanical, thermal-hydraulic and operational features of the turbine, the electrical and thermal features of the generator and the design functions of selected secondary system components at load variation (increase and decrease). Verify the design functions of major unit controllers in various mode combinations and the performance and stability of water level controllers in the turbine bleeding cycle and in the separator-reheater system. 4. Verify the Unit dynamic features and its performance at transients- trip of the last running turbine driven feedwater pump and turbogenerator idle run with the complete 6kV backup supply switching. Verify the Limitation System (LS) functions and master the unit operation at the given power range. The substage up to 75% RTP: 1. Perform calibration of the incore measurement system, of the excore ionization chambers neutron flux measurement and calibration of the temperature compensation and of the axial offset of the power range channels indications. 2. Determine the steady state Xe poisoning and the axial Xenon oscillation features. 3. Verify mechanic, thermohydraulic and operational features of the turbine and of the turbine driven feedwater pumps, condenser pumps and electrical and thermal properties of the alternator at steady- state operation at the maximum substage power. Verify the performance and stability of the major unit controllers and Control Coordinator functions 4. Verify the unit dynamic features and its performance at transients initiated by trips of major unit components- reactor coolant pumps, turbogenerator, feedwater pumps and condensate pumps. Verify the mode with 3 reactor coolant pump running. The substage up to 90% RTP: 1. Verify the neutron reactor characteristics and determine the steady state Xe poisoning. 2. Verify the mechanical, thermohydraulic and operational features of the turbogenerator set, determine the steam moisture at the steam generator outlets, verify the design functions of an optimum setting of all machine hall single parameter controllers. 3. Verify the unit dynamic features and its performance at transients initiated by the trip of one out of four running reactor coolant pumps. Master the unit operation at the given power range (preparation on full load). The substage up to 100% RTP: 1. Perform calibration of the excore ionization chambers neutron flux measurement instrumentation by the PR and WR channels, the incore measurement system and provide the correction of the PR channels indications on the flux axial difference. Determine the steady state Xe poisoning. 2. Verify at steady- state operation at the maximum power the mechanical, thermohydraulic and operational features of the turbine, electrical and thermal properties of the alternator and the performance and stability of the major unit controllers. 3. Verify the steam moisture at the steam generator outlets after made design modifications. 4. Verify the design properties of the Unit and its performance at transients following the major components trips (reactor coolant pumps, turbogenerator set, circulation water

7 406.7 pump, feedwater pump, condensate pumps,). Verify the design functions of the Limitation System. 5. Verify the turbine quick valve control and the grid stability at this test and verify the unit performance at primary and secondary control modes. 6. In the course of the 144 hours Unit trial run at the full rated power demonstrate the performance, quality and reliability of the unit equipment and its ability to be handed over into the trial operation. The Unit1 power ascension tests were successfully completed and 144 hours trial run was finished In comparison with the 6 months assumed for the completion of the planned tests in the schedule of the stage testing procedure E001, the real duration was 19 months. The major impact on the duration of the power ascension testing stage had problems connected with turbogenerator set vibrations and intensive high frequency vibrations of the inlet steam piping between control valves and the high pressure part of the turbine. These phenomena were observed during the turbine operation in the range of low output of 0-400MW. The turbine increased vibrations were caused partly due to imperfect counter balancing of the rotor system that was produced by the connection of separately balanced rotors. The counterbalancing in no load running and after turbogenerator grid connection and loading was performed, but the piping system vibration was not removed. Water draining lines and several tapping points of pressure and temperature measurement were cut off and serious leakage in the turbine control oil system was indicated. Several forced outages of the turbogenerator occurred, mainly due to the vibration and the leakage in the turbine oil system. Due to forced turbine outages the low pressure (LP) turbine rotor was damaged. It was obvious, that vibration was a complex problem, the solution of which was a necessary condition for Unit 1 commissioning to go on. An extensive program of special measurement on the turbine and piping system was implemented and the detailed analyses of the vibration were accomplished by a number of experts and specialized institutes. The experts came to the conclusion, that the main reason of the high frequency of the turbine and piping vibration was the flow of saturated steam through the control valves, where high velocities and dynamic exiting forces occurred due to high throttling at low power (high frequency pulsation in a steam flow). During unplanned Unit outage the repair works and technical modification on nonnuclear part of the Unit were carried out. The following measures were materialized: Reconstruction of the main control valves. The most feasible way of pulsating flow reduction was to change the geometry of inner channels of original control valves. A redesign of the control valve was undertaken: the plug has a flat bot and newly developed muffler is located in the front of the seat. By the reconstruction of the main control valves the problems of pulsating pressure of the steam and vibrations were solved. Reconstruction of the oil hydraulic part of the turbine control system. The oil hydraulic control system was divided into two circuits, one for the actuation of the main control valves and the second for the check flap valves. The hydraulic actuators (servomotors) were improved and the oil control system was equipped by the nitrogen accumulators. Enlargement of the running radial clearance between turbine rotor and stator. All 3 LP turbine cylinders were equipped with measurement of the radial clearance between turbine rotor and stator by contactless path indicators. Turbine operator has permanent information about the LP cylinders operating condition. Thanks to these measures all mentioned turbine diseases were successfully treated and removed. Power ascension testing started again and the process continued without any serious problem. More than 1500 individual tests were successfully performed. Power ascension testing on Temelin Unit 2 began in June 2002 and was completed in April In comparison with the original schedule of the stage testing procedures the delay

8 406.8 was 4 months. The Unit 2 stage testing procedures 2E001 divided power ascension testing into 4 substages. The substage up to 30% RTP of Unit 2 and its objectives corresponded to substages up to 5%, 12% and 30% RTP of Unit 1 and substage up to 100% RTP of Unit 2 a its objectives corresponded to the substages up to 90% and up to 100% RTP of Unit 1. The turbine of Unit 2 was operating successfully but serious problems of electrical generator occurred. The serious failure of the generator rotor occurred in the course of the primary test of the turbine generator, its exciter generator and its electrical protecting system. The Unit had to be shutdown and cooldown. The defective rotor was dismantled and sent to a manufacturing plant to identify the failure and to analyze the failure cause. It has been obvious, that the failure analyses would be a long- term matter, therefore it was decided to use a spare rotor and to continue the power ascension testing. But in the course of the primary tests of the turbine generator with spare rotor the same failure occurred. Power ascension testing had to be discontinued approximately for two months. The result of the manufacturer s investigation was, that the exciting supply leads were damaged. The reason of the damage was probably combination of moisture condensed in the exciting supply leads and its copper abrasion which resulted into the short circuit between + and pole of the exciting circuit. The manufacturer performed a set of measures including design improvement. The results of the measure corresponded to the expectation and the power ascension testing could be successfully completed. Nearly 1300 individual tests were carried out. 4 CONCLUSION Since January 2003 both Temelin Units are operating simultaneously and since May 2003 both Units are at 18 months trial operation. The electrical output of each turbogenerator set amounts to 1010 MW at the cooling water input temperature 21 o C. All completed stages of commissioning confirm that both Temelin Units meet or exceed all safety, design and operational requirements.