THE EXPERIENCE OF MATERIAL SCIENCE RESEARCH AT WWR-K REACTOR.

Transcription

1 THE EXPERIENCE OF MATERIAL SCIENCE RESEARCH AT WWR-K REACTOR. Chakrov P.V., Maksimkin O.P., Gusev M.N., Tsai K.V., Aithozhin E.S. Wienna-2008

2 NUCLEAR RESEARCHES IN KAZAKHSTAN National Nuclear Center ( works in area of peaceful use of nuclear energy. Institute of Nuclear Physics (Almaty) is one of subdivision of NNC ~700 staff Irradiation facilities Storage for radioactive materials Hot cells, etc

3 WWR-K REACTOR Operates since Heat power 6 MW. Flux up to 1.4x10 14 n/cm 2 s Outlet temperature 60 C Special high- and low-temperature loop channels. Assembly for in-reactor creep tests Reactor is used for: Science and commercial irradiation programs Researches in the field of radiation material science Researches in nuclear physics Manufacturing of radioactive isotopes for medicine The material of fuel assemblies aluminum alloy (SZAV-1)

4 CONTENT 1. Science program irradiation of lithium ceramic. 2. Corrosion research. 3. Radiation creep investigation. 4. Material science methods. 5. Most interesting results

5 LONG-TERM IRRADIATION AND INVESTIGATION OF LITHIUM CERAMICS Ceramic pebbles before (a) and after (b) irradiation Lithium ceramic (Li 2 TiO 3 + 5mol%TiO 2 ) was irradiated in WWR-K under permanent control during 223 days at 6MW of reactor power (ISTC project related to ITER activity). Conducted: Structure of lithium ceramic irradiated at C. Cross-section of irradiated ceramic pebble (Irradiation temperature 650 С) Optical metallography Density measurement Mechanical tests Tritium content measurement

6 CORROSION OF RESEARCH REACTOR ALUMINUM-CLAD SPENT FUEL IN WATER Researches were carried out from 2001 to 2005 year. Special RACK assemblies were loaded in the spent fuel storages of WWR- K. Corrosion processes (general corrosion, pit corrosion) in aluminum alloys were investigated (under IAEA research contract). Loaded assemblies,

7 LONG-TERM EXPERIMENTS ON IN- REACTOR CREEP 433 К 14,7 MPa Creep curves of aluminum (1- in reactor under irradiation, 2-initial material) Creep rate versus temperature for aluminum (1- in reactor under irradiation, 2-initial material) 2 special installation were constructed for inreactor creep tests. Some hundreds experiments were conducted. Investigated materials: Cu, Cu-alloys, Al, Cr-Ni steels, high-ni alloy (Cr20Ni45Mo3)

8 SOME OUR MATERIAL SCIENCE METHODS 1. Deformation microcalorimetry. 2. Optical extensometry. 3. Shear-Punch New (modified or extended) research methods give us the ability to use potential of research reactor more efficiently

9 DEFORMATION MICROCALORIMETRY Investigation of heat effects during deformation of irradiated materials Why do we study heat effects? Two basic reasons to stuty it: 1. Fundamental science. The heat release during plastic flow is not studied usually for irradiated materials. There are many unclear questions. 2. Practical aspects. For some materials the properties strongly depend on temperature. One needs to estimate the selfheating effect during deformation

10 DEFORMATION MICROCALORIMETRY DEVICE Micro-calorimeter (sensitivity is up to 10-7 W) combined with special miniature tensile machine. It allows us to conduct investigation of heat effect during plastic flow and destruction of irradiated metallic materials. a) Schematic of device b) Schematic of force and movement sensors c) in-cell test assembly

11 Energy balance of plastic deformation Mechanical work (A) Heat Q Annihilation of dislocations ~70-99% Annihilation of radiation defects Electromagnetic emission <1% other Energy of acoustic emission <<1% Stored energy Е S ~1-30% Generation of point defects Generation of dislocation <<1% А=Q+E s

12 Influence of irradiation on mechanical and energy characteristics of Armсo-iron 1, ini σ, MPa ε, % Fluence, n/cm 2 A, MJ/m 3 Q, MJ/m 3 E s, MJ/m ,

13 Microstructure of Armko-iron ( n/cm 2 ) 0.12 µm 0.25 µm Before deformation black-dot and dislocations Maximally deformed area (neck) Dislocation walls After deformation there are no radiation defects in microstructure. Most of black dots etc were swiped out as result of interaction with dislocations

14 1, n/cm 2 in WWR-K Influence of neutron irradiation on pure nickel Typical engineering curves initial. σ, MPa ε, % MJ/m 3 A ini n/cm Q E s 8-6 Fluence, n/cm 2 σ 02,MPa σ в,mpa ε u, % ε total, % ,

15 AIM To find the law (equation or some) for describing of heat release rate as function of strain, stress, material, fluence. dq = f(σ,ε, F ) Such equation can be used, for example, during finite element modelling

16 SMALL SPECIMEN TECHNICS: SHEAR-PUNCH Left Principle scheme of Shear-Punch test device. 1 punch, 2 top and bottom plates, 3 sample. Right Form and relative sizes of specimens: 1 standard sample for tensile test, 2 miniature sample for tensile test,, 3 specimens for shear-punch test

17 PECULIARITIES OF MODIFIED SHEAR-PUNCH Typical gap between punch and lower plate: 20-30mkm. In our assembly gap can be 300 mkm. Some advantages: Large plastic zone. Ability to investigate the destruction processes. Ability to investigate martensitic transformation in small high irradiated samples. Joint work with Dr. F.A.Garner (PNNL, USA)

18 ENGINEERING CURVES Typical tensile test curves force-elongation for steel Cr18Ni10Ti, 1 after annealing, 2 after cold work. Typical shear-punch curves force-punch displacement for steel Cr18Ni10Ti, 1 after annealing, 2 after cold work

19 CORRELATION BETWEEN TENSILE AND SHEAR YIELD STRESS Correlation relationship between yield stress in case of tensile test (σ 0.2 ) and shear-punch test (τ). annealed steel Cr18Ni10Ti; n cold worked steel Cr18Ni10Ti; annealed + cold work, steel 12Cr18Ni10Ti

20 PECULIARITIES OF SAMPLE DESTRUCTION IN SHEAR-PUNCH TEST Nickel, Non-irradiated, x700 Scheme of fracture: 1 separate zone, 2 zone of cutting, 3 zone of break. Steel Cr18Ni9Ti, irradiated 5 dpa, x350 SZAV-1, non-irradiated, x

21 MARTENSITIC TRANSFORMATION DURING SHEAR-PUNCH TEST Amount of martensitic phase (in relative units) vs. depth of punch penetration. Empty dots irradiated steel (5dpa), Filled dots annealed steel

22 AIM To be able define mechanical properties (and parameters of strain-stress behaviour from experiment with small non-standard samples Shear-punch tests Compression tests Indentation tests etc

23 TRUE STRESS-TRUE STRAIN CURVES Why true stress-strain curves? Conventional wisdom states that Highly irradiated materials permanently loses its ability for continued deformation strengthening. We want to emphasize it s not always true! Two examples will be shown. True curves are more informative

24 OPTICAL EXTENSOMETRY Camera Markers are small dots of special paint Maksimkin O.P., Gusev M.N. et al. «Method of localized deformation investigation» // «Factory Laboratory. Industry Laboratory», 11, 2006, v.72, pp This technics can be used for obtaining of true stress true strain data for high-irradiated metals and alloys and for investigation of plastic flow peculiarities and deformation localization

25 INVESTIGATION OF DEFORMATION LOCALIZATION MACROSCALE MESOSCALE 50мкм Deformation relief on surface of deformed Armco-iron ( n/cm 2 in WWR-K) MICROSCALE Defect-free channel in copper (irradiation to n/m 2 and deformation)

26 INVESTIGATION OF STRAIN AND STRESS DISTRIBUTION 12Cr18Ni10Ti, 1, n/cm 2 Tracking the movement of selected points allows to calculate strain distribution

27 APPLICATION FOR HIGH IRRADIATED MATERIALS Cr16Ni11Mo3 steel (analogue of AISI 316), 12dpa in BN-350 at ~300ºC

28 TRANSLATION FROM ENGINEERING CURVES TO TRUE CURVES Stress, Напряжение kg/mm σ, кг/мм Cr16Ni11Mo3, 15,6dpa, BN Cr18Ni10Ti (1, n/cm 2, WWR-K) Cr18Ni10Ti, unirradiated 0 0,0 0,2 0,4 0,6 0,8 1,0 Strain, Деформация rel.unit ε, отн.ед. One needs true stress-strain curve data in order to use FEMsoftware Stress, Напряжение kg/mm σ, кг/мм ,2 % 2 Ni 0 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 (Strain, (Деформация rel.unit) ε, отн.ед.) 1/

29 AIM To find the law (equation or some) for describing of deformation-plastic behavoiur as function of strain, temperature, irradiation condition, material, stress state, etc. σ = f(ε, F, T ) This equation can be used, for example, during finite element modelling of high irradiated materials

30 SOME OUR RESULTS 1. Research reactor as source of highirradiated samples. 2. Using of irradiation for suppression of dynamic strain aging. 3. Wave of plastic deformation

31 Investigation of steel Cr18Ni9 irradiated to 5 dpa in WWR-K Period of operating in reactor Irradiation temperature Damage dose Rate of damage Neutron fluence(bottom) 20 years 80 o C ~ 5dpa ~ 1.2*10-8 dpa/s cm -2 Samples were cut out from control rod of WWR-K reactor. 0.1 µm <ρ>= m -3, <d>=23nm, 5<d<60nm; Defect clusters: d < 4 nm, ρ ~ m

32 ANNEALING OF STEEL CR18NI9 IRRADIATED TO 5 DPA IN WWR-K After 1-hour annealing after irradiation 450 o C 550 o C 650 o C 0.1 µm Bright-field image o C - increase in dislocation loops concentration (ρ), decrease in mean size and disappearance of coarse dislocation loops; decrease of defect cluster contents; о С total annealing of black spots, annealing of stacking faults through dislocation reaction

33 INFLUENCE OF IRRADIATION ON DYNAMIC STRAIN AGING An influence of neutron and alpha-particles irradiation on dynamic strain aging (DSA) was investigated. It was found that in some cases (range of fluence, test s speed and temperature) irradiation can lead to the suppression of DSA and improvement of plasticity in temperature range of DSA

34 ENGINEERING STRESS-STRAIN DIAGRAMS FOR IRRADIATED STEELS Unusually large elongation Reproducible demonstration of enhanced ductility. Curve for 55 dpa specimen shifted to the right for contrast

35 Deformation behavior of steel irradiated to 55dpa in BN-350 fast reactor Stress, kg/mm 2 Deformation, rel.unit. Typical features of curve showing a deformation wave High loads (~ kg/mm 2 ) Gradual growth of load after yield drop at small deformations Wave-like character of curve During straining of 55 dpa specimen of Cr18Ni10Ti at room temperature a deformation wave appears on the surface and moves along the work axis

36 DEFORMATION WAVE ~25 sec Failure will occur here ε ~ V σ Speed of wave is ~ 0.04 mm/sec (grip speed ~0.008 mm/sec) σ Hµ

37 True stress-true strain curves for Cr18Ni10Ti steel irradiated to 55 dpa A material with a deformation wave shows an increase in deformation hardening at ε = ~ This increasing hardening stops the local deformation and moves the deformation to the next volume. 1,2 - σ(ε) 3,4 - dσ/dε(ε)

38 Martensitic γ α transformation is the cause of the deformation wave Typical amount of martensite in deformed non-irradiated sample V α is ~ 5-10 % V o lu m e fractio n o f m arten site, % Distribution of martensite along test portion of Cr18Ni10Ti specimen at 26 dpa Deformed region α Area of deformation band Cr18Ni10Ti (55 dpa) Te s t portion le ngth. m m ~ 30-35% of martensite

39 CONCLUSION In Kazakhstan the WWR-K reactor is used for researches in the field of radiating physics, for manufacture of medical isotopes, etc. In small country research reactor can serve as a "grain" or «start point» of science development and training of the scientific staff. Maximal use of opportunities of a research reactor takes place for multilateral and complex researches in various areas of science and technology. Efficiency of research reactor application can be increased by introduction of original research techniques and conducting of researches at the interfaces between sciences