The role of CVR in the fuel inspection at Temelín NPP

Transcription

1 The role of CVR in the fuel inspection at Temelín NPP Marek Mikloš, Martina Malá Research Centre Řež, Ltd. Daniel Ernst NPP Temelín IAEA TM on Hot Cell Post-Irradiation Examination and Pool-Side Inspection of Nuclear Fuel May 2011, IAEA, Smolenice, Slovakia

2 Fuel failures and main causes Monitoring of fuel failures by fuel vendors and operators Evaluation of the fuel failures data by several organization IAEA, WANO, EPRI, PIE Pool side inspections Hot cell Root causes Guidelines

3 Fuel failures and main causes PWR/VVER Grid-to-rod/debris fretting BWR Crud/corrosion [T.Allen,2006]

4 NPP Temelín 2 Units VVER-1000 Initial criticality Unit 1: October 11, 2000 Unit 2: May 31, % Power Unit 1: January 11, 2002 Unit 2: February 25,

5 Fuel system description 163 FAs in core, 61 RCCAs VVANTAGE-6 FA Based on VV5 FA WEC design Variable enrichment with radial shaping max. allowed 235 U enrichment 4.95% (+0.05%) ZIRLO TM is used as a cladding material (Improved Zircaloy-4 till 2007) Average Reload Batch ~ 42 FA s Removable top nozzle

6 Fuel problems at Temelín Incomplete Rod Insertion problems with RCCA (Rod Control Cluster Assembly) during operation FA/FR bow & twist Elongation of the fuel assemblies and rods excessive FA growth Leaking fuel rods due to grid-to-rod fretting

7 Incomplete Rod Insertion Some RCCAs (at both Units) do not drop fully to the bottom position (IRI) due to FA bow&twist Worst case - Unit 1, June 2006 test showed two RCCAs stopped above the level of the hydraulic dashpot, in other words they failed to meet the Limit Condition unscheduled outage for refueling Since the problem became known, the function of RCCAs dropping has been repeatedly tested at intervals specified by SÚJB the interval for tests was 30 days (in 2005) and is 150 days (in 2010) Based on previous tests fuel vendor: provides prediction of number of IRI for upcoming test performs a safety assessment

8 Fuel assembly/rod bow [Ernst, VVER 2010]

9 Leaking fuel at Temelín NPP Possible leakers already during first cycle Zirconium concentrations in the coolant ( 95 Zr and 95 Nb ) grid-to-rod fretting? First leakers were found during second cycle at Unit 1 During cycle: significant radioisotopes were found in the coolant During outage: on-line sipping system found 2 leakers 67 leaking fuel assemblies were found during 10 years operation Maximal total activities in the coolant through all cycles were less then 9 MBq/l a limiting value for the emergency conditions 3700 MBq/l

10 Solving fuel problems Several design changes on the linear stepper drives of RCCA made by Skoda JS Measuring system upgrade on-line gamma spectroscopy, on-line sipping, Fuel inspection and repair root causes were found Fuel design changes to make such design changes, which would not have an eminent impact on the fuel licensing process and would not required verifying of the effectiveness and functionality of design changes to loading Lead Test Assemblies (LTA) to the core and their trial operation

11 Fuel inspections and repair at Temelín NPP FRIE - Fuel Repair and Inspection Equipment Designed and manufactured by Westinghouse Electric Company LLC. More than 30 years of experiences Post Irradiation Inspection Program additional proof of PWR material compatibility in VVER water chemistry, analytical method support and verification, overall thermo-mechanical performance demonstration, independent check of the fuel system in-core behaviour FA repair

12 Fuel inspections and repair at Temelín NPP Features of FRIE Visual inspection anomalies, defects, damage extend, FA&FR length & elongate, Ultrasound inspection leaking FR Eddy Current inspection oxide and corrosion layers thickness

13 Fuel inspections and repair at Temelín NPP 67 leaking fuel assemblies since first startup of both Units 27 FA were repaired and reuse in the core Repair remove the FA top nozzle remove damage FR reinsert SS rod to the FA assemble the FA top nozzle 45% Number of repaired FR Number of non-repaired FR 55% Leaking FR is placed to a special basket made by Škoda JS

14 Fuel leakers and repairs at Temelín NPP Unit 1 Unit 2 End of Cycle # of Leakers # of Repaired Leakers # of Leaked F/Rs A End of Cycle # of Leakers # of Repaired Leakers # of Leaked F/Rs

15 Fuel problems and solutions Root causes were identified Grid-to-rod fretting Secondary hydridation Upper weld leaker Fuel assembly design was changed several times 5 designs were proposed [Ernst, VVER 2010] 4 designs were used (Zircaloy-4 ZIRLO TM, Top Nozzle and Guide Tube design changes, Stiffer skeleton, )

16 Fuel problems and solutions All above mentioned problems are under the control and all problems were solved together with the fuel vendor Last IRI in

17 Fuel problems and solutions Fuel assemblies bow was minimized Excessive fuel assembly growth was minimized as well Fuel Assembly Growth, mm T1 Growth Fast Neutron Fluence, (x 1E21 NVT) Updated Upper Limit Curve Phase 1X Growth Updated Best Estimate Curve T2 Growth T1 design: - original design - loaded to Unit 1, first core only - Zircaloy-4 T2 design - loaded to Unit 2, first core and all reloads for both Units till Zircaloy-4 Phase 0 - loaded to both Units in Zircaloy-4 Phase 1X design - all reloads from 2007 till now - ZIRLO [Ernst, VVER 2010]

18 Fuel rod separation event Fuel reconstitution was being performed on assembly BE24 One leaking fuel rod was to be removed and replaced by a SS rod After withdrawing about 150 cm of the fuel rod, the rod jerked suddenly and fractured Visual examination of the fracture location indicated the separation was caused by secondary hydriding (there had been no indications of significant hydriding from the visuals) Extensive through-wall grid-to-rod fretting was found Visual examinations of the fractured ends on both rod segments showed intact fuel pellets with no empty area, indicating that no fuel pellets were lost during the fracture event

19 Fuel rod separation event [Ernst, VVER 2010]

20 Fuel Inspection and Repair after 2011 After 10 years the Westinghouse fuel contract ended and new fuel vendor was elected Russian company TVEL New fuel TVSA-T currently manufacturing is ongoing, first fuel delivery and in-core loading August 2010, Unit 1, 163 FA May 2011, Unit 2, 163 FA New PIIP for TVSA-T is already preparing

21 New PIIP for TVSA-T Based on previous experiences International cooperation between fuel vendor and operator other companies involved too

22 Research Centre Řež Ltd. Non-profit research organization, established in 2003 Main activities Fundamental research in natural sciences using neutrons, R&D in nuclear energy related fields as corrosion processes, radiation induced damages in construction materials and other metal parts of nuclear installations, as well as in innovative neutron sources, R&D of radio-pharmaceuticals prepared by using nuclear reactors, design of new treatment procedures using neutrons

23 Research Centre Řež Ltd. Research Reactors Division Research Research reactor LVR-15, LR-0 Experimental water loops and devices PWR, BWR and VVER water chemistry Corrosion research Main goal of the reactor s facilities to model conditions that are as close as possible to real conditions, to study the effect of environment on materials in the active zone of power reactors LVR

24 Fuel cladding reliability study In 2004, 3 years project Corrosion behavior of cladding alloys under PWR irradiation simulating conditions TVEL Preparing of its continuation on the base of international cooperation RIAR Possible comparison with the real conditions FRIE at Temelín NPP

25 Conclusions One era of fuel operation at Temelín NPP is ending, another one just started Westinghouse is replaced by TVEL 10 years of satisfactorily operation several fuel problems and leakers has been occurred lots of problems were solved due to fuel inspections and repairs fuel design change how it will be with the new fuel? problems or leakers? higher volume of fission product in the primary circuit?

26 Conclusions New PIIP Visual inspection FA Single rod inspection UT inspection (KGO) Leaking FR FA measurement Bow Twist Elongation CVŘ is also involved and prepared research reactors and devices in Řež fuel repair and inspection equipment at Temelín site

27 Thank you for your attention Marek Mikloš