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Deuterium retention and release from ITER-grade
stainless steel, Be and W
Vincenc Nemanic
"Jožef Stefan" Institute, Dept. of Surface
Engineering and Optoelectronics
Ljubljana, Slovenia
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• Tritium retention data rarely obtained in fusion
  reactors (so far, only TFTR and JET used DT fuel)
  ? most of missing data needed for accurate
  modeling has to be taken in small experimental
  setups
• using T at conditions similar to those in
  tokamaks
• (high sensitivity, strict safety
  precautions, expensive)
• using D instead of T (including this study)
• (various methods combined to compensate
  lower sensitivity, additional
  data could be taken, costs greatly reduced)

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• EFDA Technology Work Programme
• TW6-TPP-RETMET
• The purpose of our study was to determine
  deuterium retention 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

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• 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 2?109
  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

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Stainless steel ITER grade (AISI 316, Co (lt0.05
wt. ) Nb (lt0.01 wt. )

• sample preparation
• cut from a massive 45 kg block 6?23?40 cm3

? 25 mm O.D tube, 50 mm high A 74.6 cm2 V
4.66 cm3 wet cleaning, drying
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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 9?10-9 mbar/s

• UHV system hot tubular extension

• exposure (0.1 mbar D2, 400C, 24 h) no
  observable isotope exchange detected

• sample in a tubular extension moved into the
  oven and heated to 400C for 8 days ? outgassing
  rate (H2) below dp/dt 9?10-8 mbar/s (i.e.
  9.21010 molec. H2/(cm2s)), registered ?C0 1.76
  ?1019 /cm3

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The recombination coefficient that governs the
outgassing at 400 C for the first 20 hours
KL(400 C) 1.8?10-24 cm4/s.
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a small difference in dp/dt detected during the
exposure ? deuterium retention determined from
isotope exchange reaction. Pure D2 "converted" in
24 h into a gas mixture
0.1 mbar
0.01 mbar
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Deuterium retention in ITER-grade stainless
steel during 24 h exposure at 400 C
No detectable level of HDO was formed.
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Deuterium retention in ITER-grade stainless steel
during 24 h exposure at 250 C
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Beryllium Brush Wellman (S-65C VHP, Ti film on
one side)
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X-ray photoelectron analysis -XPS

• XPS very surface sensitive technique
• XPS depth profiling (by Ar ion sputtering) gt
  in-depth distribution of elements

• Be covered by Be-oxide
• BeO film thickness (3 1) nm

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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

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The same quality Be (S-65C) "650C is
sufficient to remove any retained H in Be"(?!)
small TDS H2 peaks
Fig.1 a. from R.P. Doerner et al. Fus. Eng. Des
4950 (2000) 183
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TDS of the same Be sample charged by D ions
Fig.2 a. from R.P. Doerner et al. Fus. Eng. Des
4950 (2000) 183
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TDS of Be HIP sample loaded by D2 (24h, 500C,
0.13bar)
Macaulay-Newcombe RG, Thompson DA, JNM 212-215
(1994) 942
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Be "Sample 1" investigated for hundreds of hours
by the same procedure as well proved on Stainless
steel

• The amount of hydrogen extracted at 250C in 72 h
  was low, ?C 2?1016 H/cm3.

• No clear evidence of interaction with D2 at 250C
  in 24 h and 0.1 mbar ?

• Temperature increased to 400 C for 420 hours
  resulting in ?C 7.3?1017/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"

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• Some results taken on Be "Sample 2" at 400C for
  570 h
• The amount of hydrogen extracted ?C 5.5?1017
  H/cm3 ( 4.9 appm) i.e. 8?1016 H/cm2
• 2) Recombination limited kinetics 2 types of
  sites present
• a minor part 1.1?1017 H/cm3 released in the
  first 20 h (fast)
• the major part 4.4?1017 H/cm3 released 550 h
  (slow)
• 3) retention reconstructed from QMS analysis

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their ratio determined by QMS at the end of cycle
24h, 0.01 mbar
48h, 0.05 mbar
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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?
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A slow decreasing in H2 (HD, D2) kinetics and
intense isotope exchange could be only explained
when the observed ?C represents a minor part
(35?) of all H(D) assuming j KLC2

determined ?C 5.5?1017 H/cm3
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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
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Deuterium retention in ITER-grade tungsten
during 24 h exposure at 800 C (Data
incomplete, long-term heat treatment to decrease
alumina and sample outgassing, measurements in
run)
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Conclusions An UHV system with the ultimate
sensitivity of detecting 2?109 molecules/(cm2s)
from (into) the sample (30cm2) was used to
measure deuterium retention during the low
pressure isothermal exposure of ITER grade
stainless steel, beryllium and tungsten. The
achieved values are low, but in a reasonable good
agreement with published data obtained by
deuterium or tritium.
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Acknowledgement This work was supported by
Slovenian Ministry of Education, Science and
Sport and (EFDA), W6-TPP-RETMET