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2 This study is a part of two ISTC projects ## 2276 & 3672 Hydrogen and Radiogenic Helium in Metals The team involved in the study of Ni: E. Denisov, T. Kompaniets, A. Kurdyumov - St.-Petersburg State University, Russia S. Grishechkin, I. Malkov, A. Yukhimchuk - Russian Federal Nuclear Centre S. Kanashenko - Institute of Physical Chemistry, Russia R. Causey - Sandia National Laboratories, USA A. Hassanein - Argonne National Laboratory, USA M. Glugla - Forschungszentrum Karlsruhe, Germany

3 Hydrogen isotope effects on in-service metal properties: H, D, T – hydrogen embrittlement T - buildup of 3 He, which brings about an additional degradation due to: 1 - formation of He clusters and bubbles; 2 – impact on hydrogen interaction with material due to formation of new defects related to 3 He presence: i) formation of traps (stainless steel); ii )formation of facilitated paths of hydrogen release (Ni)‏

4 Techniques for creation of He concentration inside the samples Non-uniform distribution of helium Lattice damage Advantages of tritium trick technique 1. No lattice damage – recoil energy ~ 3.4 eV 2. Large samples can be charged homogeneously.

5 Tritium trick T→ 3 He+e - +ν e +18.582keV Disadvantages Aging time for creation of the necessary He concentration is high – tritium half-life 12.3 year. Aging time 1 month 1 year 3 He/T (%) 0.46 5.5 High tritium concentration is easily created only in metals forming hydrides. Other metals should be exposed to a very high tritium pressure. Exposure of metals to high tritium pressure can result in formation of vacancies (Mao, 2003 – theory, Okubo, 2000 – experiment)‏ Segregation of tritium at grain boundaries → formation of cracks

6 Tritium charging and ageing of the samples. Two different modes of tritium trick can be used to obtain the necessary concentration of 3 He.  Charging and ageing at high T and high tritium pressure.  Charging at high T and high tritium pressure. Cooling to room temperature. Ageing at room T in inert gas or air.

7 Loading SM with 3 Не by means of tritium trick in Russian Federal Nuclear Centre Ni – 99.99% purity Р tritium =500 atm Т=770K up to ~60hr ; Ageing in air, T=300K; Detritiation T=770K

8 Samples (Ni and SS) total number 547 pieces TDS samples – 0.2x2x40 mm for permeation tests For electron microscopy for mechanical tests reference samples for determination of tritium and helium content for TDS tests

9 For revealing the effects of helium three types of the samples have been studied: Type A - Initial samples. These samples annealed in vacuum at T=1170K during 5 hrs with a subsequent cooling to room temperature during 2 hrs. Type B - Helium containing samples. After the same annealing the samples of type B were exposed to tritium at T=770K and tritium pressure 50 MPa for 16 hr. After aging to a predetermined concentration the samples were detritiated at T=770K. The residual radioactivity of the samples after detritiation was of about 10 10 Bk/g. Type C – Reference samples. After the same annealing the samples of type C were exposed to protium in the manner used for type B.

10 The images of Ni surfaces immediately after preparation. Magnification factor 220. type A initial sample type B 6 appm 3 He type C exposed to H 2 Most of all defects are present in helium-containing samples. Formation of defects results in an increased embrittlement of Ni containing 3 He.

11 SEM image of Ni with 5.6 appm 3 He Molecular flow of hydrogen was observed through helium-containing membranes at room temperature

12 Thermal release of hydrogen from initial Ni. Exposure: T=770K, p=37.4 torr, t=1hr. The rate of temperature increase 0.5 K/s 1 -experiment 2 - modelling release of hydrogen dissolved in the Ni lattice

13 Temperature dependence of hydrogen diffusion coefficient in the initial sample Concentration pulse technique D=7.5. 10 - 3 exp(-40[kJ/mole]/RT), [cm 2 /s ] C – concentration at the upstream side J – downstream flux

14 Temperature dependence of hydrogen sticking coefficient on real nickel surface. s = 1.8. 10 - 2 exp(-61.4[kJ/mole]/RT)‏ At T of hydrogen release sticking coefficient is less than 10 -6 The low rate of adsorption implies the low rate of desorption → solubility is independent on surface conditions

15 Modelling Diffusion equation with boundary conditions of the third kind

16 Comparison of hydrogen release from the initial sample (1) and the sample treated in high protium pressure (2)‏ Sorption time – 1 hr, hydrogen pressure - 37.4 torr, T=770K

17 Ni with 35appm 3 He Thermal release of helium

18 Hydrogen release from initial Ni and Ni containing 3 He 1 - initial sample 2 - 6 appm 3 He 3 - 35 appm 3 He Sorption time 60min, hydrogen pressure 37.4 torr, T=770K,

19 A possible path of hydrogen release from the sample containing helium. 50μm

20 Ni (5.6 appm 3 He) Effect of prolonged annealing at 1170K 1- 3 - consecutive tests: hydrogen sorption linear heating to1170K, annealing at 1170 K, cooling to room T, etc. 4 – initial sample Exposure: T=770K, p=37.4 torr, t=1hr

21 Ni containing 10appm 3 He. immediately after detritiation annealed at T~1200K during 1800 s.

22 Summary The main effects of radiogenic helium on Ni properties are as follows 1) degradation of mechanical properties: sharp decrease in plasticity and increase in brittleness; 2) appearance of the open porosity, which becomes apparent in the changes in sorption properties and in the existence of a molecular hydrogen flow through a cold sample in permeation tests. Radiogenic helium is released from Ni at T> 1500K, which is much higher than the temperature of release of helium implanted in Ni samples by ion bombardment.

23 Future plans –Comparison of the properties of the samples obtained with high- and low temperature ageing. –Broadening the range of the studied materials: testing candidate materials for DEMO.

24 Thank you for attention!

25 Ni (5.6 appm 3 He) effect of short annealing at 1170K on hydrogen release Exposure: T=770K, p=100torr, t=1hr.

26 Thermal release of residual tritium maximum at 900K

27 Permeation Isotherms The rate of diffusion is a limiting stage of permeation The rate of adsorption is a limiting stage of permeation


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