J. Plasma Fusion Res. SERIES, Vol. 11 (2015)

Study on control of non-metallic impurities in liquid lithium
Koshiro Esaki1)*, Kazuma Hiyane1), Satoshi Fukada1),
Eiichi Wakai2), Yuzuru Ito2), Francesco Nitti2), JAEA IFMIF group2)
1) Department of Advanced Energy Engineering Science, Kyushu University
6-1, Kasuga-Koen, Kasuga, Fukuoka 816-8580, Japan
E-mail k.esaki@aees.kyushu-u.ac.jp
2)JAEA IFMIF Group(Received: 16 September 2014 / Accepted: 19 January 2015)

Experiments were performed to determine the effective operation condition of Y hot trap, to obtain actual
proof based on experimental data under the Li fluidized conditions simulating the International Fusion Material
Irradiation Facility (IFMIF), and to verify the performance change of Y hot trap when a trace amount of nitrogen isincluded in the Li. Controlling impurities in Li is essential for completion of the IFMIF. It is required todemonstrate the performance of the Y hot trap. Impurities limit goals in IFMIF are decided as < 10 wppm for D,
and < 1 wppm for T. Before initiating the present study, there was no experimental evidence whether Y can achieve
the Li purity goal for hydrogen isotope (D and T) or not. It was proved experimentally that operation of Y hot trap
at 573 K is the most stable to recover hydrogen isotopes in Li. The influence of N in Li was investigated to clarify
recovery performance of Y hot trap. It was proved Y trap can work effectively even in real IFMIF conditions toachieve the goal of Li purity limit in IFMIF.
Keywords: hydrogen isotopes, liquid lithium, yttrium, mass transport

It is necessary to measure a concentration ofhydrogen isotope in Li lower than 10 wppm in IFMIF. We
proposed a chemical dissolution method using D-depleted
H2O or HNO3 in the previous study [3]. There are several
other methods by using the hydrogen permeation orelectrical conductance, but these methods are not suitable
for absolute measurement in IFMIF from the viewpoint of
the operation temperature and the required accuracy. In thisexperiment, the hydrogen isotope concentration in Li or Y
was measured using this chemical dissolution method.

1. Introduction
In IFMIF, materials irradiation performance will beexamined. This examination plays an important role in theengineering design of nuclear fusion reactors. To performthe material irradiation test in IFMIF, high-intensity
deuterium beam is applied to flowing liquid Li, to generate
high-energy neutrons approximating nuclear fusion reactor
condition using the D-Li stripping reactions. At the sametime, nonmetallic impurities are included in the liquid Li.
Major impurities in Li are hydrogen isotopes (deuterium D,tritium T), and other species (N, C, O). Therefore, control
of non-metallic impurities in Li is required from theviewpoints of safety and Li flow stability. Impurities limitgoals in IFMIF are determined as < 10 wppm for D and <1 wppm for T [1].

In the present study, two experiments on D getteringby Y under Li fluidized conditions were performed. The
first one was experiment to realize long-time Li+Y contact
and H absorption in a vessel. The second one wasexperiment to set a Li flow condition simulating thenonmetallic impurities removal system of IFMIF and toevaluate the performance of the Y hot trap. Additionally, afew hundred wppm of N atoms is included into Li
inevitably. It is investigated whether or not N pollutes thesurface of the Y trap and causes the degradation of thehydrogen recovery performance. However, theexperimental data on how much N in Li will influence theperformance of Y are insufficient. Therefore, we evaluated
how N in Li affects the H recovery performance of Y hottrap.

Yttrium (Y) hot trap is the most effective method torecover the hydrogen isotopes in liquid Li. Y has goodcompatibility with Li and has higher solubility of hydrogenisotopes than Li. Performance of a Y hot trap wasevaluated in the previous study [2], and test results wereinvestigated based on the past experiment to recover H or
D under Li static conditions or under Li fluidizedconditions. In order to determine the most practicaloperation temperature of Y hot trap, more experimental
data are required.
author’s e-mail: k.esaki@aees.kyushu-u.ac.jp

36©2015 by The Japan Society of Plasma
Science and Nuclear Fusion Research

K. Esaki et al., Study on Control of Non-Metallic Impurities in Liquid Lithium

2. Experimental୶ ൅୶ ൅We conducted experiments to realize long-time Li+Ycontact and H absorption in a vessel. In this study, we set 3
types of experimental conditions, which are staticcondition, dynamic one without N and dynamic one with Naddition. The samples of Li (purity: 99.9%) and Y (purity:99.9%) were put in a Mo crucible and heated to 523 K, 573
K or 673 K by an electric furnace. All of Y samples weresubjected to HF treatment in order to eliminate oxide on Ysurfaces before D absorption. Oxide film on the Y surface
was removed by HF treatment, otherwise the film prevents
Y from absorbing hydrogen isotopes [4,5]. In the staticcondition, samples of Li and Y were put in a Mo crucible
and a gas mixture with a constant concentration of D2 in Ar
was supplied to the samples to absorb an arbitrary amountof D. In the dynamic condition, we used the experimental
apparatus of Fig. 1. A Y plate was put in a bottom of theMo crucible, and Li was put on the plate. In order to keep
sample’s surfaces of Li and Y fresh and clean, all thehandling was always manipulated in an Ar atmosphereglovebox (Concentration of O2: lower than 4.0 ppm).
Samples of Li were stirred by a SS-316 paddle blade with
50 mm in diameter and 5 mm in width under conditions of
the rotation rates of 50 rpm. Initially, a constantconcentration of D2/Ar mixture (approximately 1000 ppm)
was supplied to the Li + Y system for 12 hours. Weଶ  ՜ ଶ  ՜ (1)൅ ሺ ଶ ǡ ǡ ଶ ሻ୶൅ ሺ ଶ ǡ ǡ ଶ ሻ୶୶ ൅ ͵ ଷ ՜ ሺଷ ሻଷ ൅ ሺ ଶ ǡ ǡ ଶ ሻ୶(2)(3)

୶ ൅ ͵ ଷ ՜ ሺଷ ሻଷ ൅ ሺ ଶ ǡ ǡ ଶ ሻ୶ (4)The reaction vessel was composed of glass and tubesof SS-316. The apparatus was always purged with Ar gas
to prevent samples of Li or Y from contacting with air. The
reagent of D-depleted H2O for Li or HNO3 for Y wassupplied with a syringe set on the samples. The released
gases were purged out by Ar gas (purity: 99.999%). The
flow rate of Ar gas was 20 cc/min. The concentration ofgases emitted from Li and Y were determined by aquadrupole mass spectrometer (QMS). The Mg particle
bed was installed just before QMS measurements in orderto remove moisture (Q2O, Q=H, D) in released gas. Q2O ischanged to Q2 by Mg.

measured the exhaust gas composition by gas
chromatograph and converted to the quantity of D
absorbed by Li+Y. Then, we changed the gas line from
D2/Ar gas to purge Ar gas (purity: 99.999%), andwaited for arbitrary time until a specified diffusion
time elapses.

Fig. 2 Schematic diagram of the experiment apparatus
for dissolution of Y or Li
Table 1 shows experimental conditions of the samples
under static or dynamic Li with or without preliminary N2addition. We determined the distribution coefficient of D
between Li and Y.
Table 1 Conditions of samples
NoFig. 1 Schematic diagram of the experiment apparatus
for contact of Li with Y under fluidized condition

12

We used the chemical dissolution method todetermine the D concentration dissolved in Y or Li. Fig. 2
shows an apparatus prepared for the chemical analysis. D
dissolved in Li or Y was released by the chemical reactions
as described below. Hydrogen isotopes absorbed in thesample of Li were released by reaction with D-depleted
H2O. Hydrogen isotopes absorbed in the sample of Y werereleased by the reaction with HNO3. These chemical
reactions are shown below.

Static (D2)T[K]diffusiontime[hr]

573

80

amount ofsamples[mmol]
Li:50.5 Y:3.48

673

160

Li:59.6 Y:4.28

3523

4573

56dynamic(D2)

80

8673
573

Li:23.1 Y:7.42
Li:119 Y:8.26

523
573

dynamic(D2 + N2)

Li:72.6 Y:7.84

673

7937

Li condition

Li:28.6 Y:9.56
160

Li:93.4 Y:7.62
Li:115 Y:7.95

80

Li:72.4 Y:7.87

K. Esaki et al., Study on Control of Non-Metallic Impurities in Liquid Lithium

distribution coefficient calculated from the experimentalresults (No. 1~No. 9). When D recovery from Li to Y
approaches to equilibrium, the hydrogen pressures in eachsample become equal, so the equilibrium distribution
coefficient can be expressed as the ratio of two Sieverts
constants. The Sieverts’ constants under an equilibrium
condition are as follows [6,7]:஼ವǡಽ೔௄ൌ ವǡಽ೔
(5)

Fig. 3 shows the experimental apparatus for the Liforced-convection flow. The purpose of this experiment isto set a Li flow condition simulating the nonmetallic
impurities removal system of IFMIF and to evaluate theperformance of the Y hot trap. The Li flow was generated
by pressurizing the Li container with Ar gas (purity:99.999%). At the same time, the entire flow path was heldat uniform temperature higher than 453K of melting pointof Li (purity: 99.9%). The container was filled up with
1000 g of Li. The height of the Y trap, which made ofSS-316 is 260 mm, and the pore size of filter is 15 Pm. Ytrap was packed with 5.3 g of Y tip. HF treatment isperformed to the Y trap in order to eliminate oxide on Y
surface before the filling. Initially, a constant concentrationof D2/Ar mixture 1000 ppm was supplied to Li container
by bubbling. Then, Li is flown to Y trap by Arpressurization. Finally, Li sample was taken out from theflow and was analyzed by chemical dissolution method.
Table 2 shows experimental conditions of Li forced-convection flow.

஼ವǡೊ ୈǡଢ଼ ൌ ʹǤͻͶ ‫  ଺ିͲͳ כ‬ቀ

ோ்

ቁ

(6)

ቁ(7)

80

2.02E-02673

160

8.27E-03

523

4

573
dynamic(D2)6amount ofY[g]
5.3

573

3
5

Table 2 Experimental conditions

573

Static (D2)2Fig. 3 Schematic diagram of the forced-flow apparatus toinvestigate the performance of Y trap

amount ofLi[g]
1000

ோ்
଼଻ସ଻ହ

Table 3 Distribution coefficient of each samples
distribution
diffusion
Li condition
T[K]coefficienttime[hr]
CD/Li/CD/Y[-]

1T[K]ହଵଷ଻ଶFig. 4 shows the equilibrium line and experimental
values of the distribution coefficient as a function oftemperature. As seen in Fig. 4, D transfer from Li to Y
greatly depends on temperature, diffusion time and theconditions of Li. Comparing the data of Li static conditions
with those of Li dynamic conditions, it is shown thathydrogen isotope migration to Y is enhanced under Li
dynamic conditions than Li static conditions. This isbecause the diffusion distances of D in the Li dynamiccondition is shorter than that in the Li static condition.
From a viewpoint of temperature, the recovery
performance of Y is most stable when Li temperature is573 K. The distribution coefficient at 573 K is very close tothe equilibrium value.

Noflow rate ofLi[cc/min]10௄ವǡೊ ୈǡ୐୧ ൌ ͶǤ͹Ͷ ‫  ଺ିͲͳ כ‬ቀ

7

1.96E-04
80673

3.52E-03523

1.49E-03
160

573

8673
dynamic(D2 + N2)

9

3.92E-04

573

3.27E-04
1.25E-04㻌

80

1.03E-03

First, results of experiment to realize long-time Li + Y
contact and H absorption in a vessel are described. In orderto analyze behavior of hydrogen isotope migration from Lito Y, the distribution coefficient was calculated from theexperimental result. The distribution coefficient is a ratio
between the D concentration in Li and that in Y. It isdefined as the bulk D concentration in Li denoted by CD, Li
divided by the bulk D concentration in Y denoted by CD, Y.
The smaller distribution coefficient means more D istransferred from Li to Y. Table 3 shows the result of the80 hr
0.01

160 hrt= 䌲At equiliblium

At equilibrium
Static condition
Fluidized condition 160hr
Fluidized condition 80hr
Fluidized condition 80hr
N2 absorbed

1E-3

1E-4
500

600

700

800

Absolute temperature[K]9001000

Fig. 4 Theoretical and experimental distribution
coefficient38㻌

Distribution coefficient (D/Li)/(D/Y)[-]

3. Results and discussion

K. Esaki et al., Study on Control of Non-Metallic Impurities in Liquid Lithium

Fig. 5 shows the results of N2 supplying experiments(sample No. 9). The N absorption rate of Li increases
gradually. As a result, the total N atom amount in Li
reached 430 wppm after supplying Li with N2 for 2 hours.
Since hundreds wppm of N is assumed to be mixed in
actual IFMIF Li loop, this N2 supplying experiment cansimulates the IFMIF conditions. On the other hand, as seenin Fig. 4, the value of distribution coefficient for Li sample
with N absorption is larger than those without N. This isbecause N in Li delayed D diffusion and D shift from Li toY was deteriorated due to Y surface pollution. However,the value of distribution coefficient for Li sample with N
absorption is between the static conditions and the dynamic
one without N. Therefore, hundreds wppm of N is
considered not to degrade the performance of Y greatly.

inlet gasoutlet gas

D2/Ar [ppm]1000

Lithium temperature
673 [K]
Concentration of supplied D2/Ar 1381.2 [ppm]
Flow rate
100 [ccm]
Lithium weight855.6 [g]

800
600
400

supplied D 0.0524 [g]D/Li 61.2 [wppm]

20000510152025303540Time [hour]Fig. 6 D dissolution in Li by D2 gas bubblingAbsorbed N2 in Li :430.652[wppm]

900

800 Li:16.01803[g](2.308[mol]),Y:0.70[g](7.873[mmol])
700 Flow rate:100.06[ccm],Concentrarion of inlet gas:998.301[ppm]Temperature:573[K],Revolution speed:50[ccm]
600 Contact time of Li and Y in a churning state :80hr
500

Concentration of inlet gas
Concentration of outlet gas
Amount of absorbed D2400
300

0.080.06

0.040.02

200
100020406080100120

N2 absorption rate [mmol/min]

1000

Concentration of N2 / Ar [ppm]12000.10

11000

14000.00

Fig. 7 D recovery under forced convection Li flow

Time [min]Table 4 Data for recovery rate

Fig. 5 The nitrogen supply experimental result ofsample No. 9

passage timesof Y trap [-]0135Next, results of experiment for Li forced convection
flow are described. Fig. 6 shows an experimental result ofD dissolution in Li by D2 gas bubbling. The D
concentration in Li becomes so high that Li is combinedwith D and forms Li deuteride of LiD. Since the melting
point of LiD is 953 K, the fluidization of Li bypressurization is inevitable under this experimental system.
Therefore, D was supplied to Li to prevent formation ofsolid LiD by D2 gas bubbling. As seen in Fig. 6, all D2
supplied was absorbed in Li. Li including ppm-level D isformed. The final amount of D in Li was 61.2 wppm. Fig.
7 shows the result of D recovery by Y hot trap under Li
forced-convection flow. Table 4 shows the data of thisexperiment. The more times Li passed Y trap, the more Dconcentration in Li decreased. Finally the D concentrationin Li decreased to the value of 12.7 wppm. We have almostachieved the goal of D recovery in IFMIF.

Li-Y contact
time [sec]
97.9
282
418.4

D/Li[wppm]
61.2
36.3
17.3
12.7

recoveryrate [%]
59.4
71.7
79.3

4. Conclusions
We have proved that the most stable operation
temperature of Y hot trap is 573 K and demonstrated how
the N atoms included into Y through Li affect the Drecovery. Under the dynamic condition with 573 K, 80 hrand N of 430 wppm, hydrogen isotope recovery from theLi was not highly influenced by N addition. Based on theexperiment of the Li forced-convection flow simulating
IFMIF, the D concentration target of IFMIF of <10 wppm
have almost been achieved.

39

K. Esaki et al., Study on Control of Non-Metallic Impurities in Liquid Lithium

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40