Tritium Tracking by BIXS in
Contamination and Decontamination Processes

M. Matsuyama, Y. Torikai, K. Yoshida, S. Nakagawa and K. Watanabe
Hydrogen Isotope Research Center, Toyama University
Gofuku 3190, Toyama 930-8555, Japan

ABSTRACTety of kinetic energy. A part of such energetic tritium
species adsorbs on the surfaces of those materials and

The β-ray-induced X-ray spectrometry(BIXS) was

diffuses into the bulk. Those tritium will affect notapplied to evaluate contamination and decontamina-

only the recycling efficiency of the fuel in a reactor

tion behavior of tritium for four kinds of metallic ma-

core but also the safe waste management. From view-terials. Two kinds of charging methods were em-

points of decrease of tritium contamination and effec-

ployed for tritium contamination: irradiation with trit-

tive decontamination of the contaminated materials, it

ium ions at room temperature and exposure to mo-

is of great importance to understand basic tritium be-lecular tritium at elevated temperatures.

havior such as adsorption, desorption, dissolution and

The order of contamination level due to the irradiation of tritium ions was as follows:

diffusion on the surface and/or in the bulk of materials.
Although there are several methods for evaluation

Hastelloy < SS-316 ≒ Tungsten < B/SS-316,

of the adsorption amount of tritium on the surface andwhere most of the irradiated tritium was retained onof a depth profile of tritium in the bulk, those are not

the surface and/or in subsurface layers. For the decon-

still enough for nondestructive and quantitative

tamination tests of the B/SS-316 sample, it was recog-

evaluation of tritium behavior in contamination and

nized that moisture in the air plays an important roledecontamination processes. This is a reason why de-for decontamination process at room temperature.

velopment of a new tritium measuring method is re-On the other hand, it was estimated from computerquired. From this viewpoint we have proposed a new

simulation of the X-ray spectra that the SS-316 sample

measuring method for nondestructive determination of

exposed to molecular tritium at 473K was uniformly

tritium on the surface and/or in the bulk 1 : i.e.,

contaminated up to the bulk. The dissolved tritium into

β-ray-induced X-ray spectrometry(BIXS). The BIXS

the bulk could be removed about 40% by heating for 2

has been employed for determination of the consid-

hours at 473K, although the surface kept high tritium

erably small amount of tritium on an ALT-II limiter

activity.

tile exposed to D-plasma in TEXTOR 2 , and also forevaluation of diffusion behavior of tritium in bulk of

I. INTRODUCTION

Pd and Zr 3.
In this paper, the present measuring technique was

In a thermonuclear fusion reactor, the plasma fac-applied to evaluate contamination level of tritium by

ing components and construction materials are ex-ion irradiation and molecular tritium exposure to some

posed to ionic and/or molecular tritium having a vari-kinds of materials. In addition, after tritium charges

into the materials to examine decontamination behav-

structed with a flow control system of argon, and aior, changes in the X-ray spectra at room and elevatedheating system, and a collecting apparatus of tritium

temperatures were also observed, and the tritium depth

released from a sample. Details of this device are de-profiles in the bulk were evaluated by analyzing thescribed elsewhere 5.

X-ray spectra by means of computer simulation.
3. Devices for X-ray and released tritium measII. EXPERIMENTAL

urements

1. Materials
An X-ray spectrum from the tritium-containing
Four kinds of materials were employed in the pre-sample was measured by using a semiconductor de-sent study: namely, stainless steel type 316(described

tector equipped with a high pure Ge element. During a

as SS-316), SS-316 coated with a thin born

measurement, the detector and sample were kept in anfilm(described as B/SS-316), Hastelloy C-276, andargon atmosphere, and those were sandwiched withtungsten. The thickness of these materials was 0.5 mm

two lead bricks to reduce a background level of the

except for tungsten of which thickness was 20 µm.

detector. The detailed configuration of the X-ray

The SS-316 and tungsten samples was used without

measuring device is described elsewhere 2.

further treatments except for the rinse by acetone, andDuring heating of a tritium-containing sample, thethe Hastelloy C-276 sample was polished with a paper

tritium released from the sample was purged by a con-and fine abrasives before tritium charge. Boron coat-stant flow rate of argon and it was separately collected

ing on the polished SS-316 was prepared by means ofby two water bubblers to distinguish a chemical form

glow discharge in a mixed gas of diborane and heliumof the tritium species, i.e., elemental and oxidized trit-by using a specially designed device, and the thickness

ium. Activity of the collected tritium was measuredof a boron film was controlled to be about 200 nm.

with a liquid scintillation counter.

Tritium used for ion irradiation was diluted with
deuterium, and the tritium concentration was about

4. Experimental procedures

0.8 %. On the other hand, molecular tritium exposure
was carried out using a mixture of hydrogen and tritium, and the tritium concentration was 32 %.

After the initial polishing and cleaning of the samples, each was installed in the tritium irradiation device
or the molecular tritium exposure device. Before trit-

2. Devices for tritium charges and removal

ium charge, all the samples were outgassed in vacuumat 673 K.

Devices used for tritium charges by means of ion

Tritium ions were irradiated for 15 minutes at room

irradiation and molecular tritium exposure basicallytemperature, and the ion energy and current were kept

consisted of an ultra-high vacuum system and tritium

at 1 keV and about 0.7 µA, respectively. Before re-supply-recovery-storage system equipped with a hy-

moving an irradiation sample from the sample holder

drogen storage material of Zr-Ni alloy powder. Details

in the irradiation device, evacuation for one week4of these devices are described elsewhere .
The device used for tritium removal tests was con-needed to prevent contamination of the air due to tritium released from inner wall surface of the irradiation

1.5

1.5

5.0

Ar(K α )5.0

Cr(K α )

3.0

-1

1.0

4.0

Counting rate, N / counts min (∆E)

-1

Counting rate, N / counts min ( ∆E)-1Fe(Kα )

-1

-1

Counting rate, N / counts min (∆ E)-1-1
Counting rate, N / counts min(∆ E) -1

Ar(Kα)

6.0

Cr(Kα)

2.0

Fe(Kα)
1.0

0.0

0

2

4

6

8

10

12 14

16

18

Energy, E / keVMo(Lα )

0.5
Cr(K β)Fe(K β)

1.0

4.0

3.0

2.0

1.0

0.0

0

2

4

6

0

2

4

6

8

10

12

14

16

18

10

12

14

16

18

0.5

: Obs.
: Sim.

Ni(Kα )

0.0

8

Energy, E / keV

0.0

0

2

4

6

8

10

12

14

16

18

Energy, E / keV

Energy, E / keV

Fig. 1. Example of the X-rays spectra for the SS-316 sample

Fig. 2. Example of the X-rays spectra for the SS-316 sample

irradiated with tritium ions at room temperature.

exp osed to molecular tritium at 523 K for 3hours.

device.

Although conversion efficiency of β-rays to the X-rays

On the other hand, molecular tritium was exposed

for argon is not so high, argon is a practically usefulto the SS-316 samples at 523 K for 3 hours. After theprobe as a conversion gas of β-rays from viewpoints

tritium charge, to reduce tritium release from the ex-of safety and economy.

posure device the samples were cooled down and

An example of a typical X-ray spectrum is shown

evacuated at room temperature for about one week.

in Fig. 1, where SS-316 irradiated with tritium ions at

After decontamination of the device, the samples wereroom temperature was measured. As seen from thetaken out and used for observation of the X-ray spectra

figure, the most intense peak was the characteristic

and/or tritium removal examinations.

X-ray peaks of argon, which consisted of main K(α)
and minor K(β) lines though it was hard to divide

III. RESULTS AND DISCUSSION
1. Examples of the β-ray-induced X-ray spectra
for the SS-316 samples

clearly into two peaks. In addition, K(α) and K(β)
lines from constituent atoms of stainless steel such as
Fe, Cr, Ni and Mo and a broad bremsstrahlung X-ray
peak appeared.

A tritium-containing sample emits characteristic

The characteristic X-rays of argon are produced byand bremsstrahlung X-rays from bulk of the sample.

not only the collision with β-rays emitted from surface

These X-ray emissions are resulted in the interactions

tritium but also photoelectric interactions with X-rays

between β-rays and constituent atoms of the sample.

from the bulk. In this sample, the former contribution

Similarly, if the sample is kept in an argon atmosphere,is fairly larger than the latter one, because intensity ofadditional characteristic X-ray peaks of argon appear.

the characteristic and bremsstrahlung X-rays higher

1.2

0.8

0.6

0.4

3.0

2.0

1.0

0.2

0.0

4.0

8

Tritium Conc., C / 10 Bq cm

Normalized concentration, C / -

-3

1.0

Sample: SS-316
T-Charge: Exposed to molecular tritium

5.0

Sample: SS-316
T-Charge: ion irrad.

0.0

0

1

2

3
Depth, d / µm

4

5

0

10

20

30

40

50

60

70

Depth, d / µm

Fig. 3. Tritium depth profile estimated by computer simulation

Fig. 4. Tritium depth profile estimated by computer simulation

for the SS-316 sample irradiated with tritium ions.

for the SS-316 sample exposed to molecular tritium.

than the transition energy of the argon K(β) line isobserved for SS-316 exposed to molecular tritium at

weak. This indicates, therefore, that intensity of the523 K for 3 hours. The solid line is a simulation spec-

characteristic X-rays of argon gives information about

trum calculated by basing on a given depth profile

the amount of tritium retained on the surface and inwhich will be described later. The intensity of charac-

sub-surface layers of SS-316.

teristic X-rays of argon was the almost same as that of

The maximum thickness of sub-surface layers cor-the spectrum shown in Fig. 1, which suggests that the

responds to escape depth of β-rays, depending on thesurface tritium activity of both SS-316 samples was an

atomic number and density of a tritium-containing

equivalent level in spite of different tritium charges.

sample. In the case of SS-316 the thickness was esti-

However, the shape of the bremsstrahlung X-ray peakmated as about 0.1 µm. Therefore, intensity of thewas quite different. This indicates that the tritium

characteristic X-rays of argon reflects the amount of

depth profile of the SS-316 exposed molecular tritium

tritium being retained within a region of about 0.1 µm

fairly differs from that of the SS-316 irradiated withbeneath the surface.

the ions.

On the other hand, intensities of characteristic andA tritium depth profile in the bulk can be semi-

bremsstrahlung X-rays from bulk depend on not only

empirically estimated by analyzing the X-ray spectra

the amount of tritium in the bulk but also depth profile

with computer simulation. The details are describedof tritium. In addition, the shape of a broad brem-

elsewhere 1 . Figures 3 and 4 illustrate the depth pro-sstrahlung X-ray peak gives information on the depth

files obtained by analyzing the spectra shown in Figs.

profile of tritium.

1 and 2, respectively. Quite different depth profiles

Figure 2 shows an example of the X-ray spectra

were obtained: tritium charged by the ion irradiation

2.0
20

Ar(K α)

1.0

Ar(Kα)Counting rate, N / counts min-1(∆ E)-1

Mo(Kα)

15

1.0

-1
-1

Fe(K α )105Cr(K α )Mo(K α )Counting rate, N / counts min ( ∆E)

1.5

-1

Counting rate,N / counts min ( ∆E)-1-1Counting rate,N / counts min(∆E)

Ar(K α )0.15-1Ar(K α )

0

0

2

4

Fe(Kα )

6

8

10

12

Energy, E / keV

Cr(K α )

0.5

0.10

Si(Kα)

0.8

0.6

0.4

0.2
Mo(Kα )Cr(Kα) Ni(Kα )
0.0

0

2

4

6

8

10

12

14 16

18

Energy, E / keV
Cr(K α ) Ni(Kα )0.05

Ni(K α )

0.0

0

2

4

6

8

10

12

14

16

0.00

18

0

2

4

6

8

10

12

14

16

18

Energy, E / keV

Energy, E / keV

Fig. 5 Example of the X-rays spectra for the B/SS-316 sample

Fig. 6 Example of the X-rays spectra for the Hastelloy sample

irradiated with tritium ions at room temperature.

irradiated with tritium ions at room temperature.

was retained within 1 µm, but that by the molecular

0.4

tritium exposure uniformly distributed above 70 µm

Ar(Kα )Ar(Kα)

along with a high concentration region near surface.

-1
Counting rate, N / counts min(∆ E)-1

-1

0.3

-1

ium-containing material gives important information

W(Mα )Counting rate, N / counts min (∆E)

Namely, the X-rays induced by β-rays in a trit-

2.0

about contamination level such as tritium activity on
the surface and tritium distribution in the bulk.
2. Examples of the β-ray-induced X-ray spectra
for the B/SS-316, Hastelloy, and W samples

0.2

1.5

W(Mα)

1.0

0.5

W(Lα )
0.0

0

2

4

6

8

10 12 14 16 18

Energy, E / keV

0.1
W(Lα )

Figures 5, 6 and 7 describe the X-ray spectra observed for B/SS-316, Hastelloy and W irradiated withtritium ions at room temperature. The same irradiation
conditions were applied to all the samples mentioned

0.0

0

2

4

6

8

10

12

14

16

18

Energy, E / keV

above. For B/SS-316 sample, weak characteristic
X-rays of the base material appeared in spite of coat-Fig. 7 Example of the X-rays spectra for the tungsten samples

ing with boron film. It seems that this is due to theirradiated with tritium ions at room temperature.

contribution of backscattering of β-rays.
The intensity of Ar K(α) line from B/SS-316 was(∆ E)In argon flow

In the air

Counting rate, N / counts min-1

10: 0min: 10min: 140min

4.0

-1

100

I / counts min

Intensity of characteristic X-rays of Ar

-1

5.0

3.0

2.0

1.0

Sample: B/SS-316
1

0.0
1

10

100

0

2

Elapsed time, t / hr

4

6

8

10

Energy, E / keV

Fig. 8. Change in intensity of the characteristic X-rays of argon

Fig. 9. Change in X-ray spectrum by the isothermal heating atwith time in an argon flow and in the air at room temperature.

473 K for the SS-316 sample exposed to molecular tritium.

The flow rate of argon was 40 cm3/min.

An examination was carried out using the B/SS-316
the highest in the three samples: 20 times greater thansample irradiated with tritium ions, and the result was

Hastelloy, and 10 times greater than W. Irradiation

shown in Fig. 8. The X-ray measurements were con-area of W was about 5 times smaller than that of

tinuously conducted in an argon flow with a given

B/SS316 sample. This is the main reason why the in-time interval from the initial measurement for 24 hours,

tensity for W sample is remarkably smaller than thatand after that the sample was stored in the air except

for B/SS-316. In addition, it is considered that very

for measuring time of the X-rays.

weak intensity for Hastelloy is due to desorption in the

Decrease of the X-ray intensity in the argon flow

evacuation process for one week after tritium irradia-

was very small, but it was accelerated by the storage intion.

the air. There are two possibilities for the decrease of

Although the intensity of the bremsstrahlung X-ray

the X-ray intensity: one is due to desorption from thespectra was greatly different, there was a little differ-surface, and another is due to diffusion into the bulk.

ence in shape for three samples, indicating a fairly

For the present case, the former possibility is dominantsmall different depth profile near surface region. It isbehavior. If the latter possibility is advantageous, asuggested, therefore, that most of the irradiated tritium

large difference in the decreasing behavior will not bein these materials did not diffuse into the bulk and it

expected in the different atmosphere.

remained near surface region.

The decreasing curves in Fig. 8 could be apparently described by the following equation:

3. Tracking of a decontamination process by
BIXS

Ix = k t – n ,-------------- (1)where Ix represents the intensity of the characteristic
X-rays of argon, k the proportional constant, t the time

The present measuring method was applied toand n the factor of time dependency. The value of n in

examination of the desorption behavior of the irradi-

the argon flow was estimated to be –2.6x10-2 , and that

ated tritium. Change in the amount of surface tritiumin the air was –1.3. Namely, this indicates the decrease

was followed from change in the intensity of charac-in the amount of surface tritium was assisted 50 times

teristic X-rays of argon with time at room temperature.

by exposure to the air containing suitable moisture.

Normalized intensity of X-rays,I / -Counting rate, N / counts min

-1

( ∆E)

-1

1.0

Initial
0.4

0.3
10 min later

0.2
140 min later

0.1

0.8

0

2

4

6

8

10

0.8

0.6

0.6

0.4

0.4

0.2

0.2

0.0

0.0

1.0

: Remaining Tritium: Ar(Kα): Fe(Kα): Cr(Kα): Mo(Kα)

0

20

40

60

80

100

120

Fraction of remaining tritium,F / -

0.5

0.0

140

Time, t / min

Energy, E / keV

Fig. 10. Enlarged spectra of bremsstrahlung X-rays shown in

Fig. 11. Changes in intensity of the characteristic X-rays and trit-

Fig. 9.

ium inventory observed for the SS-316 sample during the is othermal heating at 473K.

Effects of moisture in argon on desorption rate of trit-

exposed to molecular tritium. Enlarged spectra are also
illustrated in Fig. 10. Although spectral intensity totally decreased with time by desorption of the dissolved tritium, shape of the bremsstrahlung X-ray
spectra was not similar. It is clearly seen in the energy
region from 3.5 to 5 keV, where the ramp of curves
becomes gentle with heating time. This indicates thatthe tritium concentration became low near surface re-

4.0

5.0
4.0

-8

Tritium Conc., C / 10 Bq cm

the isothermal heating at 473 K for the SS-316 sample: 0min: 10min: 30min: 140min

5.0

Tritium Conc., C / 10-8 Bq cm -3

Figure 9 shows change in an X-ray spectrum by-3

ium are similarly recognized for other materials 5.

3.0

3.0
2.0
1.0
0.0

2.0

0

2

4

6

8

10

12

14

Depth, d / µm

1.0

0.0

0

10

20

30

40

50

60

70

Depth, d / µ m

Fig. 12. Change in tritium depth profile estimated by analyzing
the X-ray spectra shown in Fig. 9

gion.
All the intensities of the characteristic X-rays of
constituent atoms in SS-316 decreased similarly withmarkably low. This agrees with the change in sha pe ofthe bremsstrahlung X-ray spectra shown in Fig. 10.

heating time, which is shown along with the fraction

Figure 12 demonstrates the tritium depth profilesof remaining tritium in Fig. 11. The fraction of re-estimated by analyzing the X-ray spectra shown in Fig.

maining tritium was evaluated from the total desorp-

9. The initial depth profile shows that the dissolvedtion amount which was finally determined by heating

tritium uniformly distributed up to 70 µm excepting

the sample at 1073K. It should be noticed that a steep

near surface region. After heating at 473 K for 10 min,decrease appeared in the intensity of Mo(Kα) line

however, considerably law concentration appeared in athough the fraction of remaining tritium gradually de-wide region from about 1 to 10 µm though a subsur-

creased, indicating that tritium concentration did notface region below 1 µm was still kept at high concen-

uniformly decreased. Namely, it is suggested that only

tration. In addition, it was seen that high concentration

tritium concentration near surface region became re-near surface region has remained even after heating for

-1

2.5

Sample: B/SS-316

Ar(K α)
20

2.0

15

1.5

Fe(K α)

10

1.0

5

0

0.5

300

400

500

600

700

0.0
800

Characteristic X-ray intensity of Fe, I(Fe) / counts s-1

Characteristic X-ray intensity of Ar, I(Ar) / counts s

25

Annealing Temp., T / K

tamination process was examined at room temperatureand elevated temperatures, i.e. isothermal and isochronal heating. From these examinations, the following results were obtained:(1) Almost same amount of tritium ions was irradiatedat room temperature, but the amount of tritium retained in the materials significantly differed. The orderof the retained amount was as follows.
Hastelloy < SS-316 ≒ Tungsten < B/SS-316

Fig. 13. Changes in intensity of the characteristic X-rays observed for the B/SS-316 sample during the isochronal heating.

(2) Exposure of molecular tritium to SS-316 was conducted at 523 K for 3 hours, and a uniform depth pro-

140 min. This indicates that tritium trapped near sur-file in the bulk was established, although a considera-

face region was strongly fixed by trap sites such as OH

bly high concentration region existed near surface.

groups formed on metallic oxides.
Examination of isochronal heating was conducted(3) From the decontamination test of B/SS-316 in thefor the B/SS-316 sample irradiated with tritium ions.

ambient air, it was suggested that moisture in the air

The result is shown in Fig. 13. Heating in vacuum wasplay an important role for decontamination efficiency.

carried out for 30 min at each annealing temperature.

In addition, decontamination at elevated temperatures

The intensity of Ar(Kα) line as well as Fe(Kα) line

indicated that it is possible to remove tritium relatively

began to decrease at about 500 K, and it reached about

low temperatures.

15% of the initial intensity at 773 K. Similar results
were obtained for boron coating graphite. Furthermore,(4) An interesting change in the tritium depth profiles

the bremsstrahlung X-ray spectra indicated no diffu-

appeared in a decontamination process at 473 K forsion into the base plate of stainless steel. Namely, it

SS-316. Further investigations are needed to elucidate

was seen that the irradiated tritium on the boron film

the decontamination mechanism in detail.

can be removed by heating at a relative low temperature and boron coating is useful for the decrease of

REFERENCES

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Assay

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Materials

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K.H. Finken and K. Watanabe, “Nondestructive

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MeasurementsofSurface

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