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FAST NEUTRON FLUX EFFECT ON VVER RPV’s LIFETIME ASSESSMENT

Influence of atomic displacement rate, neutron spectrum and irradiation temperature on radiation-induced ageing of power reactor components. FAST NEUTRON FLUX EFFECT ON VVER RPV’s LIFETIME ASSESSMENT. D . Е rak Ya . Shtrombakh , P . Platonov , А. А maev , Yu. Kevorkian, А. Chernobaeva

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FAST NEUTRON FLUX EFFECT ON VVER RPV’s LIFETIME ASSESSMENT

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  1. Influence of atomic displacement rate, neutron spectrum and irradiation temperature on radiation-induced ageing of power reactor components FAST NEUTRON FLUX EFFECT ON VVER RPV’s LIFETIME ASSESSMENT D. Еrak Ya. Shtrombakh, P. Platonov, А. Аmaev, Yu. Kevorkian, А. Chernobaeva Research Institute of Atomic Reactors Dimitrovgrad - Ulianovsk, Russia October 2005 RUSSIAN RESEARCH CENTER “KURCHATOVINSTITUTE”

  2. Why we should investigate Neutron Flux Effect in VVER RPV’s materials radiation embrittlement The Investigation Program carried out Conclusions, further works Some words about VVER-1000 CONTENTVVER-440

  3. RPVsVVER-440

  4. Two generation of VVER-440 type units are in operation:VVER-440/230 and VVER-440/213

  5. RPVsVVER-440/230 End of Life: NVNPP-3 - 2001 NVNPP-4 - 2002 KolaNPP-1 - 2003 KolaNPP-2 - 2004

  6. RPVsVVER-440/213 End of Life: RovnoNPP-1 - 2011 RovnoNPP-2 - 2012 KolaNPP-3 - 2012 KolaNPP-4 - 2014

  7. VVER-440/213 surveillance programs

  8. The problems of VVER-440/230 RPV • All VVER-440/230 RPVs were annealed because of extremely high rates of radiation embrittlement of the core welds • Re-irradiation embrittlement kinetics determines RPV steels lifetime • Re-irradiation embrittlement Data Base is highly restricted

  9. CUTTING OF TEMPLETS ALLOWED TO OBTAIN FIRST ACTUAL RESULTS OF THE 1ST GENERATION RPV MATERIALS PROPERTIES

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

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

  12. Are the irradiation conditions of specimens equal to RPV wall conditions?TemperatureNeutron Flux Is it correct to use the results of irradiated specimens for RPV lifetime assessment?

  13. Direct measurements of irradiation temperature carried out with thermocouples in surveillance channels of Kola NPP-3 showed that overheat of surveillance specimens as compared to RPV inner surface in the core region does not exceed 5°C. Tracing scheme of thermocouple COBRA project results SS temperature Input water temperature

  14. Neutron flux on SS 10-20 times higher than on inner surface of RPV wall Flux on SS Core center SS capsules Core center Reactor pressure vessel Core barrel

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

  16. Materials

  17. High flux irradiation –Аrmenia-2 (full core)Low flux irradiation – Rovno-1 (reduced core)Irradiation temperature -270оС

  18. Experimental data matrix consists of 52 points

  19. Function dependence DTК=AFF0.33 waschosenas in Russian Guide 95% upper and lower boundaries: Comparison of the data obtained after irradiation by high and low dose rates

  20. The statistical test was used for the evaluationofdifference between high and low fluxes data It tests the hypothesis that corresponding coefficients (AF) of two models are equal. Small (< 0.05) Р-values means that hypothesis should be rejected (on 95% significance level), and each data group should be described by its own model. Otherwise two data groups should be described by one model.

  21. The results ofexperimental data evaluation by statistical test

  22. Р-value=0.610.05

  23. Р-value=0.04  0.05

  24. Р-value=0.01  0.05

  25. All experimental data

  26. Experimental data for materials with high Cu-content show significant flux effect

  27. For flux effect evaluation the difference in ΔTKwas used:d= Δ TK(low flux)- Δ TK(high flux)for the fluence 4x1019 сm-2.

  28. Correlation parameters (R) between d and P and Cu contents Dependence of flux effect on Cu content seems to be

  29. Flux effect dependence on Cu content.Preliminary estimation:effect is significant if Cu content more than ~0.13 %

  30. The results of mechanical tests of the VVER-440 pressure vessel steels show that copper influence on ТК shift is insignificant for re-irradiation

  31. It agrees with the data of microstructural studies of the steels in irradiated and annealed conditions, and after re-irradiation

  32. The microstructural studies of VVER-440 materials carried out by P. Pareige,O. Zabusovand others, B. Gurovich, Е. Кuleshovaand others show the following: At primary irradiation of the RPV steelsthe copper-enriched clusters occur. They are of 2-3 nm in diameter with high distribution density and are effective barriers for dislocation movement. There is depletion of solid solution by copper atoms.

  33. Cu distribution in VVER-440irradiated weldP.Pareige, O.Zabusov, M.Miller etc.

  34. Copper content does not change in solid solution during annealing, there is coagulation of copper-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.

  35. Cu in irradiated, annealed and re-irradiated VVER-440 weld

  36. Copper precipitate in irradiated, annealed and re-irradiated VVER-440 weld

  37. The dependence of transition temperature shift for VVER-440 pressure vessel materials on neutron flux is not expected under re-irradiation.

  38. Results of templets material study

  39. 1.The work concerning establishment of fast neutron flux influence on radiation embrittlement for VVER-440 pressure vessel materials has been carried out using standard VVER-440 RPV materials irradiated in the surveillance channels at high of ~31012сm-2s-1 and at low ~41011сm-2s-1 fast neutron fluxes. 2. Flux effect occurs in VVER-440 pressure vessel materials with the level of copper content higher than ~ 0.13 %. CONCLUSIONS (1/2)

  40. 3. Radiation damage under re-irradiation does not depend on copper significantly. 4. It is confirmed by the data of microstructure studies. 5. There is no dependence of transition temperature shift for the VVER-440 pressure vessel materials on neutron flux under re-irradiation after annealing. CONCLUSIONS (2/2)

  41. The studies made within the last 10 years enables NPPs extend the life time of annealed units for 15 years with licensing for each 5 years

  42. The quantitative assessment of flux effect for different values of fluence is necessary for the solution of practical problems of VVER-440/213 lifetime assessment. It requires development of models for radiation embrittlement under irradiation at high and at low fluxes in wide range of fluence , based on modern understanding of mechanisms of microstructural changes under irradiation. Line of the further works

  43. Neutron flux corresponds to RPV wall Representative data onKola NPPUnit 3 and 4RPV steels radiation embrittlement Application of the reconstitution technique provides representativenes of test results

  44. RPVsVVER-1000 Low P and Cucontents High Ni content in weld metal (Up to 1.9 %) EOF depends on the primary Radiation Embrittlement Elaborating RE depends are based on SS and research results

  45. SS assembly VVER-1000 Research assembly

  46. Melting monitors from VVER-1000 irradiation programsSurveillance program Research program 314°C 308°C 302 °C 292 °C288°C 304°C 300°C293°C

  47. The capsules with surveillance specimens are located above the core baffle in a place with high neutron flux gradient

  48. It is very important to use results with high accuracy fluence data

  49. New radiation embrittlement dependence of VVER-1000 RPV steels based on SS and research results TF = 28 + 8,4Ni1,5F1/3 The standard reference dependence specified in the Russian Guidefor weld seams: TF = 20 F1/3

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