Post on 27-Mar-2015
"Jožef Stefan" Institute,Dept. of Surface Engineering and Optoelectronics
Slovenian Fusion Association (SFA). MHEST
Deuterium retention in
ITER -grade: stainless steel, Be and W
Vincenc Nemanič, Bojan Zajec, Marko Žumer
Ljubljana, Slovenia
Cadarache, 15th June 2009
2) Experimental methods:
• general description • selection and adaptation for our work.
3) Results on ITER - grade stainless steel, Be and W
1) Motivation for the work
Outline of the talk:
Motivation: tritium retention prediction
Basic concepts to predict tritium retention data for metals
applied in future fusion reactors:
1) Deuterium data obtained in experiments simulating and
approaching conditions in ITER post mortem analysis
2) Refined classical experiments for more accurate
interaction data (equilibrium & kinetics) of gaseous
hydrogen (H/D) with ITER relevant metals = our
approach
An important fact: Most of solubility, diffusivity and
permeability data obtained decades ago.
EFDA Technology Work Programme:
TW6-TPP-RETMET
The purpose of our study was to determine deuterium
retention in 24 hour-expositions in D2 at p = 0.1 mbar
and below
• ITER grade AISI316 at T = 100, 250 and 400 °C• ITER-grade Be T = 100 °C and 250 °C• ITER-grade W T = 250, 400 and 1000 °C
Sample metals provided by
EFDA Close Support Unit - Garching
Experimental: Basic interaction of hydrogen (H/D/T) with
bulk material is expressed by diffusivity and solubility,
experimentally determined by:
1) infusion/outgassing technique
or
2) membrane technique
A careful selection of all experimental details is needed to
get reliable results. W. G. Perkins, J. Vac. Sci. Technol. 10 (1973)
543
The principle of infusion/outgassing technique:
equilibrium between gas phase (H/D/T) and metal sample
achieved at specified conditions (high p, high T) gas
pumped off transient to a new equilibrium observed
(low p).
* * * *
The principle of permeation technique:
Transient flow observed from t = 0 when pupstream is set
until steady downstream flow is achieved
Hydrogen detection mode applied in any of both techniques:
1) Dynamic method, ion current of characteristic mass
number applying mass spectrometer is recorded at
constant pumping speed
or
2) Static method (gas accumulation), pressure recorded by
non-ionizing gauges in valved-off system followed by mass
spectrometry, instrument located in a separate UHV system
Both techniques types require low hydrogen background since
it influences the sensitivity (and discrimination limit when
deuterium is applied).
The most troublesome is outgassing of the sample holder and
its potential simultaneous interaction with hydrogen (H/D).
Isotope exchange interaction difficult to distinguish since it
runs: in the sample and in the sample holder.
Best option for H.metal interaction is applying both
techniques ifusion/ourgassing and permeation, since they
give complementary data.
Materials most suitable for sample holder:
Kovar glass: almost ideal up to 450 °C, no detectable
interaction with H/D. (used in our lab for ITER-grade
stainless steel and Be)
Silica: wide range of T, thermal shock resistance, used for
RF heating, but exhibits anomally, noticed in:
A.Farkas, L.Farkas, Trans.Farad. Soc. 31, 821 (1935)
and quantified inR.W.Lee, R.C.Frank, D.E.Swets, J.Chem.Phys., 36, 4 (1962).
A minor part of hydrogen is “diffusive”, isotope exchange
in silica or quartz using D2 unpredictable, quantified work
with metal samples troublesome or impossible.
Materials most suitable for sample holder:
Pure alumina: at present, the only candidate for W sample
holder from 500 °C to 1000 °C.
Several exposures of empty thimble to deuterium showed
some isotope exchange, too. Resolving the difference
when the sample in hot zone or cool zone, still
troublesome.
Experimental setup
(3 UHV chambers) for
infusion/outgassing or
for permeation method
using H2 or D2
Exposure section with calibrated cell, CM and SRG gauges
Exposure section – thimbles: glass or alumina
The ultimate sensitivity determined by the background
outgassing rate of H2 and small volume (~1.3 L).
Inner sources of H2 are:
• UHV system walls (at R.T.)• metal sample (elevated T)• sample holder i.e. extension tube (elevated T)
•QMS (ionization cell itself)
The achieved detection limit ~ 2109 molecules/(cm2s)
Various schedules used to convert QMS signals of H2, HD
and D2 into the absolute units by calibration H2/D2 mixtures.
Equal procedure steps applied for all investigated metals
Results:
Stainless steel ITER grade
(AISI 316, Co (<0.05 wt. %); Nb (<0.01 wt. %)
25 mm O.D tube,
50 mm high
A = 74.6 cm2
V = 4.66 cm3
wet cleaning, drying
1) sample preparation
2) cut from a massive 45 kg block 62340 cm3
Experimental steps applied for stainless steel
(similar for Be and W (glass replaced by alumina))
"blank run" steps (sample at R.T.):
• UHV system after bake-out: dp/dt= 910-9 mbar/s
• UHV system + hot tubular extension
• exposure (0.1 mbar D2, 400°C, 24 h) no observable
isotope exchange detected
• sample in a tubular extension moved into the oven and
heated to 400°C for 8 days outgassing rate (H2) below
dp/dt = 910-8 mbar/s (i.e. 9.2×1010 molec. H2/(cm2s)),
registered C0 = 1.76 1019 /cm3
Pressure vs. time curve composed from several cycles,
the importance of low outgassing is evident.
0 5000 10000 15000 20000 25000 300000.0
0.2
0.4
0.6
0.8
1.0
C
t / s
measuredDLM RLM calc exponential
The observed kinetics is governed by the RLM rather
than by the DLM
0 20 40 60 80 100 120 140 160 180 200109
1010
1011
1012
1013
1014
RLM calculatedmeasured
q / m
olec
. H2 /
(s c
m2)
t / h
Devation from the RLM noticed after 20 h when
hydrogen from strogly bound sites became prevalent
p t N/A C mbar h atom D/cm2 at D/cm3 1 0.1 24 1.8×1016 2.9×1017
2 0.1 24 2.6×1016 4.2×1017
3 0.01 24 1.9×1015 3.0×1016
4 0.01 24 1.9×1015 3.1×1016
Deuterium retention in ITER-grade stainless steel
during 24 h exposure at 400 °C
No detectable level of HDO was formed.
Deuterium retention in ITER-grade stainless steel
during 24 h exposure at 250 °C
p t N/A C mbar h atom D/cm2 at D/cm3 1 0.01 24 6.2×1014 1.0×1016 2 0.01 24 5.5×1014 8.9×1015 3 0.1 24 4.3×1015 7.0×1016
More details: V Nemanič, M Žumer, B Zajec, Nucl. Fus., 48, 11,
115009 (2008)
Beryllium Brush Wellman (S-65C VHP, Ti film on one side)
tile size: 2.42.00.4 cm3
A = 26.24 cm2
V = 3.84 cm3
Ti film removal,
wet grinding,
cleaning, SEM,
EDXS, XPS
X-ray photoelectron analysis -XPS• XPS: very surface sensitive technique
• XPS depth profiling (by Ar ion sputtering) => in-depth distribution of elements
Be covered by Be-oxide BeO film thickness ~ (3 ± 1) nm
Beryllium – hydrogen (H,D,T) interaction
• published data on diffusivity and solubility very
scattered and almost useless for prediction of results
(A.A. Pisarev, Fusion Techn., 28, (1995) 1262)
• no data about hydrogen amount in our sample available
• a few reports on the same Be quality found as a rough
guidance for scheduled measurements
Be "Sample 1" investigated for hundreds of hours by the
same procedure as well proved on Stainless steel
• The amount of hydrogen extracted at 250°C in 72 h
was low, C ~ 21016 H/cm3.
• No clear evidence of interaction with D2 at 250°C in 24
h and 0.1 mbar
• Temperature increased to 400 °C for 420 hours
resulting in C ~ 7.31017/cm3 (6.5 appm) of hydrogen
• Kinetics perturbed presumably by traces of Ti film
deuterium retention data could be innacurate
• Further precautions introduced for "Sample 2"
Some results taken on Be "Sample 2" at 400°C for 570 h
1) The amount of hydrogen extracted C ~ 5.51017 H/cm3 (~
4.9 appm) i.e. ~ 81016 H/cm2
2) Recombination limited kinetics – 2 types of sites present
a minor part ~1.11017 H/cm3 released in the first 20 h (fast)
could be analog to “diffusive” H in silica?
the major part ~4.41017 H/cm3 released 550 h (slow) could be
analog to slowly releasing H in silica at high T
3) retention reconstructed from QMS analysis
24 h averaged H2, (D2,HD) flux
0.E+00
1.E+10
2.E+10
3.E+10
4.E+10
5.E+10
6.E+10
0 100 200 300 400 500 600
t / h
H2(
D2,
HD
)/cm
2 s
extraction
D2 exposure
24h, 0.01
mbar
48h, 0.05
mbar
their ratio determined by QMS at the end of cycle
p t N/A C mbar D2 h atom D/cm2 atom D/cm3 1 0.01 24 2.7×1015 1.8×1016 2 0.01 24 2.5×1015 1.7×1016 3 0.05 48 1.7×1016 1.2×1017 4 0.05 48 1.3×1016 8.7×1016
The amount of retained deuterium at specified exposures
What could be the amount of H(D) still contained
in the sample that makes isotope exchange possible?
9.0E+179.5E+171.0E+181.1E+181.1E+181.2E+181.2E+181.3E+181.3E+181.4E+181.4E+18
0 100 200 300 400 500 600
t / h
del
ta C
/ (
H/c
m3)
2.E-27
3.E-27
4.E-27
5.E-27
6.E-27
7.E-27
8.E-27
9.E-27
1.E-26
KL /
cm
4 /s
C estim
KL
A slow decreasing in H2 (HD, D2) kinetics and intense isotope
exchange could be only explained when C in 560 h represents a
minor part (35%?) of all H(D) assuming j = KLC2.
determined
C ~ 5.51017 H/cm3
Tungsten Plansee
rod size:
O.D.= 2.5 cm
h = 20 cm
machined to
a tube:
I.D. 2.2cm
h = 5 cm
V = 5.31 cm3,
A = 76.0 cm2
Initial experiments in silica using RF heating gave
unreliable results due to:
• simultaneous outgassing of hydrogen and
• isotope exchange during deuterium exposure,
manifested in high HD ratio
• HD could not be attributed to W only
Hydrogen solubility from 400 °C to 1100 °C calculated from trusted (?) data.
Alumina data: Serra, J. Am.Ceram. Soc., 88 (2005) 15-18
Tungsten data: Frauenfelder, JVST, 6 (1969) 388-397
Silica data: RW Lee, RC Frank, DE Swets, J Chem.Phys., 36 (1962) 1062-1071 (diffusive H)
0.0007 0.0008 0.0009 0.0010 0.0011 0.0012 0.0013 0.0014 0.0015
1013
1014
1015
1016
1017
C /
H/c
m3
1/T / 1/K
alumina W silica
800°C
0.0007 0.0008 0.0009 0.0010 0.0011 0.0012 0.0013 0.0014 0.00151E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
D /
cm2 /s
1/T / 1/K
alumina W silica
Hydrogen diffusivity from 400 °C to 1100 °C calculated
from trusted reported data.
800°C
For ~ 2 mm thick materials, 24 h at 800 °C means:
Fo = 0.04 for alumina – will not come to equilibrium
Fo = 9.5 for silica
Fo = 130 for tungsten
In 48 h at 800 °C, alumina released dN/dA = 6.71015 H2/cm2
leading to dN/dt 1.31010 H2/(s cm2), low
W sample inserted intense outgasing
in 45 h C = 1.051018 H/cm3.
Residual outgassing at the end: H2 80%, CO 20%
deuterium exposures
Deuterium retention in ITER-grade tungsten
during 24 h exposure at 800 °C in alumina
1 2 3 4 5 6 7 8 9
p m/e m/e m/e m/e dN/dA C dN/dA
mbar 2 3 4 28 (CO) 1015D/cm2 1016D/cm3 1014D/cm2 1 0.0110 0.26 0.49 0.25 <0.01 3.0 4.3 3.8 2 0.0095 0.20 0.48 0.33 <0.01 2.9 4.2 3.6 3 0.0094 0.14 0.44 0.42 <0.01 3.3 4.7 3.9 4* 0.0102 0.64 0.32 0.05 <0.01 1.1* 1.6* 2.2 5 0.0098 0.45 0.44 0.12 0.26 4.1 5.9 4.2
Table 3: Retention of deuterium in tungsten at p = 0.01 mbar and T = 800 °C in 24 hours. The amount is reconstructed from the total pressure change and gas composition at the end of exposure. The number in the first column is exposure number. Exposure No.4 with * was done in hydrogen, but the released deuterium comes from the sample and the thimble loaded previously. Retention of deuterium is expressed as number of atoms per unit area in column 7 and as number of atoms per unit volume in column 8. The amount of deuterium released in the first 24 h after exposure is given in column 9.
Conclusions
An UHV system with the ultimate sensitivity of detecting ~
2109 molecules/(cm2s) from (into) the sample (A~30 cm2)
was built to measure deuterium retention during the low
pressure isothermal exposure of ITER grade stainless steel,
beryllium and tungsten.
High amount of H2 extracted in long term extractions from all
three metals prior exposures were feasible.
The setup is prepared now also for:
• complementary permeation measurements (Stainless steel,
Be, W) or tritium permeation barrier films
• “post mortem” analysis of suitable shaped D loaded samples.
We are interested for cooperation.....
Acknowledgement
This work was supported by MHEST and SFA and by
(EFDA), W6-TPP-RETMET.
Thanks for your attention.