Radiation Embrittlement and Neutron Dosimetry Aspects in WWER-440 Reactor Pressure Vessels Life Time Extension

Transcription

1 Second International Symposium on Nuclear Power Plant Life Management Radiation Embrittlement and Neutron Dosimetry Aspects in WWER-440 Reactor Pressure Vessels Life Time Extension Erak D.Yu. Kochkin V.N, Kevorkian Yu.R., Zaritsky S.M., Chernobaeva A.A., Shtrombakh Ya.I. RRC Kurchatov Institute INSTITUTE OF REACTOR MATERIALS AND TECHNOLOGIES

2 Contents Task description Existed problems in WWER-440 RPVs lifetime extension Investigations and activities have been done Substantiation of possibilities of WWER-440 RPVs lifetime extension WWER-440 RPVs lifetime management

3 Degradation Scheme Properties changing RPV loading

4 RPV materials properties have Ductile-Brittle Transition Region T kf

5 Degradation Scheme

6 Procedure of the assurance of RPV material irradiation lifetime Obtaining the representative experimental results for providing forecast of material properties changes Development of the material irradiation embrittlement model Confirmation of the material irradiation embrittlement model conservatism accepted for the calculations

7 WWER RPV EOL Basically Depends on Weld Seam Radiation Embrittlement Generation 1 Generation 2 VVER - 440/230 VVER - 440/213 VVER Up Up to to 0,22% 0,22% Up Up to to 0,22% 0,22% < 0,08% Up Up to to 0,048% Up Up to to 0,027% < 0,012% < 0,3% < 0,3% 1,2-1,9% 1,2-1,9%

8 First problems appeared in ensuring of WWER-440 (1-st generation) RPVs lifetime (middle 80-th th) Absence of Т К0, С Р, С CU data for RPV materials situated in core region Absence of surveillance specimens programs First SS results from other NPPs showed high level of radiation embrittlement for welds #4 materials doing impossible to operate up to end of design lifetime

9 Ways for solving of WWER-440 (1-st generation) RPVs lifetime (middle 80-th th) Annealing of welds #4 recovering of properties Putting of demy assemblies in core reducing of radiation loading of RPVwall Materials tasks Assessment of annealing effectiveness (level of properties recovering after annealing) Determination of re-irradiation after annealing behavior of WWER- 440 weld materials

10 ANNEALING OF RPVs IN COREZONE - PROBLEM - SOLVING Investigations had shown a real possibilities for properties recovering of irradiated WWER- 440 RPV materials From 1987 to WWER-440 RPVs were annealed

11 RPVs VVER-440/230 Unit Start Annealing Templet cutting P, % Weld 4 Cu, % Ni, % NVNPP , , 1995, NVNPP-4 KolaNPP , <0.2 KolaNPP End of Design Lifetime: NVNPP NVNPP KolaNPP KolaNPP NPP

12 ANNEALING REGIMES APPLICATED TO RUSSIAN RPVs RPV Start of operation Annealing Annealing regime NVNPP-3 NVNPP ±20 С 150h 475±15 С 100 h NVNPP ±15 С 150 h KolNPP ±15 С 150 h KolNPP ±15 С 150 h

13 CUTTING OUT OF TEMPLETS GOOD OPPORTUNITY TO MONITOR REAL RPV MATERIAL CONDITION

14 CUTTING OF TEMPLETS FROM WWER-440 RPVs Unit Start of operation Annealing Cutting NVNPP , , 1995 NVNPP , 1995 KolNPP KolNPP

15 First templets results showed effectiveness of annealing procedure The only way to predict RPV material behavior accelerated irradiation in VVER-440 SS channels

16 LIFE TIME EXTENSION EXPERIENCE FOR WWER-440 FIRST GENERATION RPVs I 2 c T F I 1 I 2 L 4 0 I 2 v 0 T a F l u e n c e, c m - 2 I 2C conservative approach I 2L lateral shift I 2V vertical shift

17 The lateral shift model was specified by Gosatomnadzor RF for re-irradiation embrittlement assessment Т R = - T res + ( Т res3 + А F3 F R ) 1/3, where А F = 800 (P Cu); T res =Т к0 - T ка Archive metal is absent Surveillance programs are absent Т к0 values under RPV construction were not defined

18 The conservativeness of the Lateral shift model

19 REIRRADIATION OF TEMPLETS WAS PERFORMED IN VVER /213 SURVEILLANCE CHANNELS Location scheme of the surveillance chains in VVER-440/213 pressure vessel Full core Reduced core high flux irradiation low flux irradiation

20 Is it correct to use the results of irradiated specimens for RPV lifetime assessment? Are the irradiation conditions of specimens equal to RPV wall conditions? Temperature Neutron Flux

21 Direct measurements of irradiation temperature carried out with thermocouples in surveillance channels of Kola NPP-3 3 showed that overheat of surveillance specimens as compared to RPV inner surface in the e core region does not exceed 5 C. 5 COBRA project results Tracing scheme of thermocouple ,6 269,7 271, Temperature, "С Heat power, %

22 Core center Neutron flux on SS times higher than on inner surface of RPV wall Core center Flux on SS SS capsules Reactor pressure vessel Core barrel

23 Flux effect study is very important for VVER-440 RPV lifetime assessment. In 1987 special program was started

24 High flux irradiation Аrmenia-2 (full core) Low flux irradiation Rovno-1 (reduced core) Irradiation temperature о С Fluence х 10 19, см -2 (E>0.5 MeV) P-0.022% Cu-0.10% P-0.013% Cu-0.08% P-0.028% Cu-0.12% P-0.028% Cu-0.18% P-0.036% Cu-0.13% RPV wall ss channel full core Flux х 10 11, см -2 с -1 (Е>0.5MeV)

25 All experimental data low flux high flux y = x T K (experimental), o C correlation between predicted and experimental values for low flux T K =800(P+0,07Cu)F 1/3, o C correlation between predicted and experimental values for high flux

26 Experimental data for materials with high Cu-content show significant flux effect low flux high flux y =x T K (experimental), o C correlation between predicted and experimental values for low flux correlation between predicted and experimental values for high flux T K =800(P+0,07Cu)F 1/3, o C

27 The results of mechanical tests of the WWER-440 pressure vessel steels show that copper influence on Т К shift is insignificant for re-irradiation T K, o C Cu, %

28 The microstructural studies of WWER-440 materials carried out by P. Pareige, O. Zabusov and others, B. Gurovich, Е. Кuleshova and others show the following: At primary irradiation of the RPV steels the copper-enriched enriched clusters occur. They are of nm in diameter with high distribution density and are effective barriers for dislocation movement. There is depletion of solid solution by copper atoms.

29 Copper content does not change in solid solution during annealing, there is coagulation of copper-enriched enriched clusters and formation of copper precipitates of diameter ~ 5 nm with much smaller distribution density. Large copper precipitates formed during annealing are of low density They are not effective barriers for dislocation movement There is no more intensive formation of copper clusters at re- irradiation.

30 It agrees with the data of microstructural studies of the steels in irradiated, annealed and re-irradiated conditions P.Pareige, O.Zabusov, M.Miller etc. CC Irradiated material Re-irradiated material

31 Preliminary Conclusions 1. Flux effect occurs in VVER-440 pressure vessel materials with the high level of copper content. 2. Radiation damage under re-irradiation does not depend on copper significantly. 3. It is confirmed by the data of microstructure studies. 4. There is no dependence of transition temperature shift for the VVER-440 pressure vessel materials on neutron flux under re- irradiation after annealing. 5. It allows to consider neutron flux and Cu content as insignificant parameters at re-irradiation.

32 Results of templet material study

33 TYPICAL TEMPLET RE-IRRADIATION DATA

34 Difference of VVER-440 RPV materials behavior under primary irradiation and re-irradiation Irradiation primary irradiation 200 T K (exp), o C Re-irradiation T K =800(C P +0.07C Cu )F 0.33, o C T K (exp), o C re-irradiation T K =800(C P +0.07C Cu )F 0.33, o C

35 NEW MATERIAL Therefore, according to stated above it is possible to assert that condition of WWER-440 RPV weld material after primary irradiation and annealing differs from its condition in unirradiated condition. It makes unreasonable to use embrittlement models for primary irradiation (like Lateral shift ) as analogs for re-irradiation embrittlement Actually we refer to new material received by known radiation-temperature treatment of initial metal. Hence, construction of adequate embrittlement model for reirradiation (after annealing) should be based on re-irradiation experimental data.

36 SPECIAL RESEARCH PROGRAMS FOR DATA BASE EXPANDING AND DEVELOPMENT OF NEW MODEL OF RE-IRRADIATION EMBRITTLEMENT (PRIMAVERA PROJECT)

37 Database parameters < P < < Cu < cm -2 < F < cm -2 ~ cm -2 c -1 < ϕ < ~ cm -2 c -1

38 PROJECT OF EXPERIMENT-STATISTICAL MODEL T k re-irr = A F (P-P 0 ) n F m (σ =19.5) A F, P 0, n, m parameters P A F = 570 P 0 = n = 0.7 m = 0.38

39 Comparison of calculated and experimental results T k re-irr = 570 (P-0.025) 0.7 F 0.38

40 RPV DOSIMETRY

41 Uncertainties in neutron fluence determination on RPV play a key role in lifetime evaluation Several years of operation

42 Neutron dosimetry of RPV Ex-vessel fluence monitoring VALIDATION Cutting probes from inner surface of RPV Neutron calculations Evaluation and prognosis of neutron fluence on the inner surface of RPV

43 Azimuth distribution of neutron flux on the inner surface of WWER-440 with dummies with full core

44 Axial distribution of neutron flux on the inner surface of WWER-440 with dummies with full core flux, Е>0.5 МeV, см -2 с E E E E E E E E E+10 weld 4 core center 12.5 deg, 30.0 deg flux Е>0.5 МeV, см -2 с E E E E E E E E E+10 weld 4 core cente 12.5 deg 30.0 deg 1.0E Distance from the core bottom, см 1.0E distance from the core bottom, см

45 TEMPLETS CUTTED FROM THE INNER SURFACE OF WWER-440/230 Definition of the real data on radiation embrittlement, Reirradiation mechanisms study and development of new models Microstructural study: TEM, APFIM, SANS Neutron Fluence specification on the inner surface of RPV Relative distribution of fast neutron flux on the templet

46 Calculated and measured distribution of 54 Mn activity on the weld No.4 and base metal of Kola RPVs A, 10 6 Bq/g steel Weld No.4 Level of core middle A, 10 6 Bq/g steel Weld No.4 Level of core middle Azimuth coordinate, degree Kola Azimuth coordinate, degree Kola-2

47 Ex-vessel measurements on the WWER-440 Azimuth location of irradiation device with neutron dosimeters near the RPV Level of the core center Level of weld 4 Irradiation device RPV

48 WWER-440 with reduced core Calculated and experimental activities of 54-Mn (weld 4) 7.0E E E+05 B q /g ram m 4.0E E E E Mn activity, calc 54-Mn activity, exp 0.0E Azimuth angel, deg.

49 Conclusions (1/2) The studies with templets re-irradiation made within the last years enables NPPs extend the life time of annealed units for 15 years with licensing for each 5 years The project of experiment-statistical model for re-irradiation embrittlement of WWER-440 RPV materials has been developed. The experiment-statistical model developed describes adequately the WWER-440 RPV materials behavior under reirradiation. For final model verification it is necessary to obtain additional representative experimental results on re-irradiation of WWER- 440 RPV materials.

50 Conclusions (2/2) Development of the new model of re-irradiation embrittlement can provide lifetime extension of some of the 1-st generation of WWER-440 units for more than 15 years Measurements of 54 Mn activity in the templates cut out from RPV inner surface give the valuable information for RPV dosimetry validation Decreasing of uncertainties in neutron fluences determination for RPV wall is necessary to extend theirs lifetime