Steam Generator Ageing Management in Slovakia current practices and related issues

Transcription

1 International Atomic Energy Agency Meeting on Update and Upgrade of IAEA-TECDOC on Ageing Management of Steam Generators IAEA, Vienna, June 2009 Steam Generator Ageing Management in Slovakia current practices and related issues Martin Březina

2 Content of the presentation Introduction of VUJE company Basic description of SG WWER 440 SG in Slovak republic Operational problems and other issues Technical upgrades of SG WWER 440 Ageing management programs Conclusions

3 Introduction of the company VUJE a.s. An engineering company that performs design, supply, implementation, research and training activities, particularly in the field of nuclear and conventional power generation

4 Introduction of the company The company performs all activities related to the design, construction, operation, reconstruction and decommissioning of the following energy installations and systems: nuclear power plants hydro-electric power plants, fossil-fuel power plants and heating plants with coal, gas and oil used as fuel power plants and heating plants for waste wood combustion wind power plants high-voltage transmission lines kv high-voltage distribution plants development and supply of simulators used for training the operating personnel of power plants, distribution plants, ships, chemical plants information systems designed for the control of energy systems automated control of water supply systems

5 Department of structural analysis Main tasks: Analysis of the effects and mechanisms of material degradation and evaluating the level of damage Irradiation damage monitoring of RPV materials using surveillance samples Monitoring corrosion and erosion of materials in selected systems of both primary and secondary systems Failure analysis of operational defects in equipment by evaluating material conditions

6 Description of SG WWER 440 The steam generator is horizontal shell-and-tube heat exchanger It consists of a pressure vessel, a horizontal heat exchange tube bundle, two vertical primary collectors, a feedwater piping system, moisture separators and steam collector Primary coolant enters the steam generator through a vertical collector, travels through the horizontal U-shaped submerged stainless steel tubing, and exits through a second vertical collector The tube ends penetrate the collector wall and are expanded using either a hydraulic or explosive expansion process and then welded at the collector inside wall surface Both the collectors and heat exchange tubes are made of Tistabilized austenitic stainless steel The steam generator vessel is a carbon steel horizontal cylinder consisting of forged shells, stamped elliptical ends and stamped branch pipes and hatches welded together

7 Main parameters of SG WWER 440 Parameter Unit Value Parameter Unit Value Thermal power [MW] Coolant flow rate in tubes [m/s] 2,71 Steam capacity [kg/s] 125 Specific heat flux (average) [kw/m 2 ] 89,23 Pressure of steam [MPa] 461 Total heat exchanging surface [m 2 ] 2576,6 Steam temperature [ C] 258,9 Total number of tubes 5536 Feedwater temperature [ C] Diameter of tube [mm] 16 Coolant temperature at steam generator inlet Coolant temperature at steam generator outlet [ C] 295 Thickness of tube walls [mm] 1,4 [ C] 267 Tube mean length [m] 9,26 Coolant flow rate [m 3 /h] 7100 Coolant pressure [MPa] 12,26 Pressure loss along the coolant path Steam humidity at steam generator outlet [MPa] 0,075 [%] 0,25

8 Scheme of SG WWER 440

9 Main welds of SG WWER 440

10 Main welds of SG WWER 440

11 Structural materials of SG WWER 440 Content of elements [mass %] Materials C Si Mn S P Cr Ni Cu Ti V Mo As Nb 08Ch18N10T 0,08 0,8 2,0 0,020 0, xC-0, K 1 0,19-0,26 0,2-0,4 0,75-1,0 0,030 0,030 0,3 0,3 0, K 0,16-0,24 0,15-0,30 0,35-0,65 0,040 0,040 0,25 0,25 0, ,17-0,24 0,17-0,37 0,35-0,65 0,040 0,040 0,3 0,3 0, Ch1MF 0,22-0,29 0,17-0,37 0,4-0,7 0,025 0,030 1,5-1, ,15-0,3O 0,25-0, Ch 3 0,36-0,44 0,17-0,37 0,5-0,8 0,025 0,025 0,8-1,1 0,3 0, Ch2MFA 0,22-0,27 0,17-0,37 0,3-0,6 0,025 0,025 2,8-3,3 0,4 0,3-0,25-0,35 0,6-0,8 0,8 - ChN35VT 4 0,12 0,60 1,0-2,0 0,015 0, ,1-1, W=2,8-3,5 UONI13/25 5 EB123-JE 0,11 0,18-0,5 0,65-1,2 0,033 0, ,0 - - AN-42 *, Sv08GSMT 6 0,12 0,3-0,9 0,8-1,6 0,030 0,030 0, ,2-0,4 - - EA 400/10T 5 0,1 0,6 1,15-3,1 0,025 0,025 16, ,3-0,75 2,0-3,5 - - EA 395/9 5 0,12 0,7 1,0-2,2 0,025 0,025 13, ,5-7,5 - - ZIO-8 5 0,12 1,0 2,7 0,030 0,030 23, , EA 898/21B 5 0,1 0,7 1,6-2,5 0,025 0,025 17, , ,3-1,05-0,8-1,05 Sv 04Ch19N11M3 6 0,1 1,0 0,8-2,0 0,020 0,030 15, ,5-3,0 - - Sv 07Ch25N13 7 0,09 1,2 0,8-2,0 0,020 0, , , Sv 08Ch19N10G2B 7 0,1 1,0 1,3-2,5 0,020 0,030 17,5-20 8, ,7-1,2 Sv 10Ch16N25M6 6 0,12 1,2 0,8-2,0 0,020 0,030 12, ,5 - -

12 Scheme of SG WWER steam generator body, 2 - primary cold leg collector, 3 - primary hot leg collector, 4 - manhole, 5 - heat exchanger tubes, 6 - vertical distance grid, 7- horizontal distance grid, 8 - feedwater pipeline, 9 - separator, 10 - perforated sheet, 11 - steam header, 12 - primary circuit header cover, 13 - secondary circuit header cover, 14 - cover seals for the primary and secondary circuit, 15 - secondary circuit seal cover monitoring location, 16 secondary circuit air vent, 17 - primary circuit seal cover monitoring location, 18 - primary circuit air vent, 19 - header periodic blowdown, 20 - steam generator periodic blowdown, 21 - steam generator permanent blowdown, 22 - nozzle, 23 - pipe unions for steam generator level checking

13 SGs in Slovak republic Bohunice V-1 NPP operation terminated 12 (2 x 6) (SU production) Bohunice V-2 NPP under operation 12 (2 x 6) (Czech rep. - Vitkovice production) Mochovce Unit 1,2 under operation 12 (2 x 6) (Czech rep. - Vitkovice production) Mochovce Unit 3,4 under construction 12 (2 x 6) (Czech rep. - Vitkovice production) Total 48

14 Operational problems and other issues a) Crack of the hot leg collector SG 32 in Bohunice NPP (1987) b) Cracking of ligaments on the hot leg collector SG 31 in Bohunice NPP (1987) c) Cracking of primary collector bolts d) Cracks on primary collector flange (1995) e) Leaky secondary circuit cover seal (2002) f) Leaky hot collector impulse lines (1999, 2007) g) Analysis of heat exchange tubes + brief summary of plugged tubes

15 ad c) Cracking of primary collector bolts Cracking of the primary collector bolts long-lasting problem Material austenitic stainless steel, type ChN35VT-VD with a high content of Ni Mechanical properties increased - result of complicated thermal treatment thermal hardening Example of the thermal treatment: > anealing 1000 C/50min/water > 1. hardening 840 C/10h/water > C/49h/water Unwanted result high level of sensitization to IG corrosion and to IGSCC Solution lower pre-stressing of the bolts replacement of the seal Ni ring Camprofile gaskets (grooved)

16 ad c) Cracking of primary collector bolts Material characterization: Chemical composition [mass %] C Mn Si P S Cr Ni Ti W ChN35VT-VD max. 0,12 1,0 až 2,0 max. 0,60 max. 0,025 max. 0,015 14,0 až 16,0 34,00 až 36,00 1,10 až 1,50 2,80 až 3,50 Mechanical properties t = 20 C t = 350 C Rp 0,2 Rm A 5 Z KCU2 Hardness Rp 0,2 [MPa] [MPa] [%] [%] [%] [HB] [Mpa] ChN35VT-VD min

17 ad c) Cracking of primary collector bolts Primary collector bolt - M48

18 ad c) Cracking of primary collector bolts Indication in nut part History: 5x / 10y 1y Cracks in thread heel Max. depth 8,0 mm

19 ad d) Cracks on primary collector flange Indications on primary collector flange and on first threads Material austenitic stainless steel type 08Ch18N10T Mechanism IG SCC Solution modification of the flange, precise tightening of the bolts

20 ad f) Leaky hot collector impulse lines

21 ad g) Analysis of heat exchange tubes Three tubes only were cut off and dragged out of SGs Only in one case the indication was found confirmed by metallographic evaluation Indication = repaired tube weld metal δ-ferrite magnetic phase All tubes were in a good condition, no ageing processes observed

22 ad g) Summary of plugged tubes Number of plugged tubes: Bohunice Unit #3 Bohunice Unit #4 SG No. Tubes Plugged Plugged [%] SG No. Tubes Plugged Plugged [%] SG ,192 % SG ,235 % SG ,090 % SG ,126 % SG ,885 % SG ,445 % Total Σ ,662 % SG ,054% SG ,000% SG ,018% SG ,199% SG ,000% SG ,018% Total Σ ,048% Mochovce Unit #1,2 less then Bohunice Unit #4

23 Technical upgrades of SG WWER New feedwater distribution system

24 Technical upgrades of SG WWER Primary collector covers with end stop

25 Technical upgrades of SG WWER Primary collector flange sealing Camprofile gasket (grooved) instead of Ni ring

26 Corrosion monitoring system in SG A simple equipment enables a long-term exposition of various samples inside the steam generator above the primary collector flange The samples are placed on a special holder into secondary circuit conditions The program has been interupted due to construction changes of primary collector cover XJ8 XJ9 XJ10 XJ11 XJ12 XJ13 XJ14 XU14 XU13 XU12 XU11 XU10 XU8 XU8 XJ1 XJ2 XJ3 XJ4 XJ5 XJ6 XJ7 XU7 XU6 XU5 XU4 XU3 XU2 XU1

27 Ageing management programs The ageing management program for steam generators, is supported by chemistry measurements to support evaluation of the impact of ageing on involved materials and material conditions, and reduce the intensity of the erosion - corrosion mechanism Cumulative fatigue damage is calculated and evaluated on a basis of temperature and pressure changes measured during operation: SG wall steam collector nozzle feedwater nozzle primary collector - hot leg

28 Fatigue damage of SG wall

29 Fatigue damage of steam collector nozzle

30 Fatigue damage of feedwater nozzle

31 Fatigue damage of hot leg primary collector

32 Conclusions SGs are very reliable components of NPPs type WWER 440 Total number of plugged tubes is still negligible Operational regime has been set to optimal parameters Used structural materials are stable in given standard conditions and make possible to extend the life of NPPs Applied or prepared ageing management programs can ensure safety and reliable operation for the planned and extended lifetime, too