HYDROGEN INTERACTION WITH NICKEL

CONTAINING RADIOGENIC HELIUM

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

Hydrogen isotope effects

on in-service metal properties:

H, D, T – hydrogen embrittlement

T - buildup of 3He, 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 3He presence:

i)formation of traps (stainless steel);

ii)formation of facilitated paths of hydrogen release (Ni)

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. C

C

C n

3 4H e , H e

T ritiu m“ tr ic k ”

H O W H E L IU M C O N C E N T R AT IO N IN S O L ID C A N B E C R E AT E D ?

so lid

Tritium trick T→3He+e-

+νe+18.582keVDisadvantages

Aging time for creation of the necessary He concentration is high – tritium half-life 12.3 year.

Aging time 1 month 1 year 3He/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

Tritium charging and ageing of the samples.

Two different modes of tritium trick can be used to obtain the necessary concentration of 3He.

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.

Loading SM with 3Не by means of tritium trick

in Russian Federal Nuclear CentreNi – 99.99%

purity

Рtritium

=500 atm

Т=770Kup to ~60hr ;

Ageing in air, T=300K;

Detritiation T=770K

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

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 1010Bk/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.

The images of Ni surfaces immediately after preparation.

Magnification factor 220.

type A initial sample

type B 6 appm 3He

type Cexposed to H

2

Most of all defects are present in helium-containing samples.Formation of defects results in an increased embrittlement of Ni containing 3He.

SEM image of Ni with 5.6 appm 3He

Molecular flow of hydrogen was observed through helium-containing membranes at room

temperature

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 -experiment2 - modelling

400 600 800 10000

2

4

6

8

10

J x

101

3 , H

2/s

T,K

1

2

release of hydrogen dissolved in the Ni lattice

Temperature dependence of hydrogen diffusion coefficient in the initial sample

1,2 1 ,3 1 ,4 1 ,5 1 ,6 1 ,7 1 ,8 1 ,9 2 ,0 2 ,1-6 ,5

-6 ,0

-5 ,5

-5 ,0

-4 ,5

lg(D

[cm

2 /s])

1000/T

800 750 700 650 600 550 500T,K

Concentration pulse technique

D=7.5.10-3exp(-40[kJ/mole]/RT), [cm2/s]

C – concentration at the upstream side

J – downstream flux

Temperature dependence of hydrogen sticking coefficient on real nickel surface.

1,2 1 ,3 1 ,4 1 ,5 1 ,6 1 ,7 1 ,8 1 ,9 2 ,0

-8 ,0

-7 ,5

-7 ,0

-6 ,5

-6 ,0

-5 ,5

lg(s

)

1000/T

s = 1.8.10-2exp(-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

Modelling

∂C x,t ∂ t

=D∂2C x,t ∂ x2

C x ,0=C0 ,x∈0, l

D∂C x,t ∂ x

=bC2 ,x=0

∂C x,t ∂ x

=0, x=l/2

Diffusion equation with boundary conditions of the third kind

Comparison of hydrogen release from the initial sample (1) and the sample treated in

high protium pressure (2)

300 400 500 600 700 8000 .0

0 .2

0 .4

0 .6

0 .8

1 .0

2

J X

101

4 , H

2/s

T,K

1

Sorption time – 1 hr, hydrogen pressure - 37.4 torr, T=770K

Ni with 35appm 3He Thermal release of helium

1520 1540 1560 1580 16000

1

2

3

4

5J

x 1

014 , 3 H

e/s

*sa

mp

le

T,K

Hydrogen release from initial Ni and

Ni containing 3He

300 400 500 600 700 8000,0

0,2

0,4

0,6

0,8

1,0

3

2

1

J x

1014

, H2/

sam

ple

T,K

1 - initial sample

2 - 6 appm 3He

3 - 35 appm 3He

Sorption time 60min, hydrogen pressure 37.4 torr, T=770K,

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

50μm

Ni (5.6 appm 3He) Effect of prolonged annealing at 1170K

300 400 500 600 700 8000,0

0,2

0,4

0,6

0,8

1,0

4

3

2

1

J x

1014

, H2/

sam

ple

T,K

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

Ni containing 10appm 3He.

immediately after detritiation

annealed at T~1200K during 1800 s.

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.

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.

Thank you for attention!

Ni (5.6 appm 3He)effect of short annealing at 1170K on

hydrogen release

200 400 600 800 1000 1200 14000

5

10

15

20

25

30

J x

1013

, H2/

sam

ple

t,s

0

200

400

600

800

1000

1200

T,K

Exposure: T=770K, p=100torr, t=1hr.

Thermal release of residual tritium

900 1000 1100 1200 1300 1400 1500 16000

50

100

150

200

250

300

J, a

rb.u

nits

t, s

700

800

900

1000

1100

1200

1300

T,K

maximum at 900K

Permeation Isotherms

0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.00

0.05

0.10

0.15

0.20

0.25

+

+ +

+

+

+ +

+

+

o

o o

o

o o

o

o

J, a.u. aaaa.a.u.a.u. o

(p up , torr) 0.5

The rate of diffusion is a limiting stage of permeation

The rate of adsorption is a limiting stage of

permeation