Journal of Nuclear Materials 191-194 (1992) 158-162North-Holland

journal ofnuclear

materials

Compatibility test of Be with Li 20 (1) - diffusion couple test

Naoki Sakamoto b, Hiroshi Kawamura ", Etsuo Ishitsuka a and Yoshinori Ichihashi a

a Japan Atomic Energy Research Institute, Oarai Research Establishment, Oarai-Machi, Higashi Ibaraki-Gun,Ibaraki-Ken 311-13, Japan

b NGK Insulators, Ltd., Maegata-Cho I, Handa-Shi, Aichi-Ken 475, Japan

The tritium breeding blanket in a fusion reactor is the essential component to collect thermal energy and tritium. Thehelium gas-sweep/water-cooled blanket has been recommended as a concept design in the Japan Atomic Energy ResearchInstitute (JAERI). In this blanket, beryllium as neutron multiplier may be contacted with lithium oxide as tritium breedingmaterial. In this case, the compatibility between beryllium and lithium oxide is one of the most important issues. Therefore,the out-of-pile compatibility test has been carried out by means of a diffusion couple of beryllium and lithium oxide whichwas inserted in the capsule container filled with high purity helium gas.

As a result of this test, beryllium evaporated on the lithium oxide side was clearly observed. However, reaction productswere not detected by X-ray diffraction on the beryllium interface that is in contact with the lithium oxide. Beryllium collapseby oxidation and penetration of lithium-diffused layer into beryllium was observed.

Table 1The results of chemical analysis on beryllium specimens

high temperature, and then polished. Cleaning of theberyllium specimens was done by ultrasonic washingwith acetone.

2.1.2. Lithium oxideThe lithium oxide specimens arc sintcred pellets

(80%T.D.) made by Mitsubishi Atomic Power Ind.,inc .. Their dimensions are 10 mm diameter and 5 mm

1. Introduction

Beryllium has been used as neutron reflector inJMTR, because its thermal, mechanical and nuclearproperties are suitable [1]. On the other hand, beryl­lium is promising as neutron multiplier, with lithiumoxide as tritium breeding material [2]. It is expectedthat the operation temperature range of this blanket is450-750oe [3]. Therefore, the evaluation of thermal,nuclear and tritium release characteristics arc indis­pensable to usc this breeding blanket [4].

From this point of view, the irradiation tcst thatsimulate the structure of the tritium breeding blankethave been planned at JMTR [5]. Therefore, the out­of-pile compatibility test of beryllium with lithium ox­ide was carried out by inscrting a diffusion couple ofberyllium and lithium oxide into the capsule containerfilled with high purity helium gas.

2. Experimental

2.1. Specimen

2.1.1. BerylliumThe beryllium specimens are hot-pressed beryllium

disks made by NGK Insulators, Ltd .. Their dimensionsare 10 mm diameter and 1.4 mm thickness. Theirpurity is about 99 wt.%. The results of a chemicalanalysis of the beryllium specimens are shown intable 1. The main impurity was beryllium oxide. Hot­pressed beryllium cut down into plate was wrappedwith mild steel (SS41), rolled at 900oe, reformed at

Chemical component

BeBeDAlBCdCaCCrCoCuFePbLiMnMgMoNiSiAgCIN

Analysis value (wt.%)

99.281.280.03200.000090.00020.00310.09500.0110.00070.00210.06100.00200.00030.01000.00900.00190.0200.02360.00040.00300.0380

0022-3115/92/$05.00 © 1992 - Elsevier Science Publishers B.V. All rights reserved

N. Sakamoto et al. / Compatibility test of'Be with LilO 159

Zry- 2 W Spring

was investigated by visual observation for each speci­men. Then, the reaction products on the belylliuminterface were identified by X-ray diffraction. UsingCrKa, this examination was carried out before andafter washing away extraneous matter 9n the contact­ing interface by a ultrasonic washing equipment. Then,the lithium-diffusion characteristic in depth and theoxidation characteristic on the beryllium interface wereinvestigated by ion microanalysis (IMA).

The lithium-diffusion characteristic was evaluatedby the thickness of the lithium-diffused layer. The ation was used as primaty ion for IMA. The primary ionbeam was narrowed down to a diameter of about 1 f.lmin order to perform the surface analysis at 1000 magni­fication. qBe ion images, 7Li ion images and all ionimages were obtained in this analysis.

AI203 Zry-2Fig. 1. The outline of the capsule. 3. Results and discussion

3.1. Observation of appearance

104/T. K- 1

Fig. 2. Vapor pressure of beryllium over beryllium, and lithiumover lithium oxide.

7001000

T,K

2000 1500

-15Be over BeLi over Li,O

-205 10 15

CD Kudo.at al. : raf. r8)

CD (J) Ikeda. et al. : ref. (l)

\, @ Kimura.at al.: ref. [9)

CD A.James StonehouseE - 5

''r-,~; ref. (6)....

<l1

a.: ® 'I'Ol -100

@

As a result of visual observation and X-ray diffrac­tion on the outside and the interface, evaporated beryl­lium was identified on the lithium oxide side. Thethickness of this evaporated beryllium layer was seento increase with increasing annealing temperature andtime. Transformation and crack were not observed.

The vapor pressure of beryllium over beryllium [6],and that of lithium over lithium oxide [7-9] is shown infig. 2. This figure shows that the vapor pressure onberyllium is higher than that on lithium oxide in this

2.3. Procedure

The outline of the capsule is shown in fig. 1. Adiffusion couple of belyllium disk and lithium oxidepellet was' inserted into the capsule container made ofZry-2. Then, after filling the capsule with high purityhelium gas (6N) at 1.0 X 10 5 Pa, the capsule is sealedby tungsten inert gas (TIG) welding. All components ofthe capsule are degassed at 900°C before the assem­bling. The diffusion couple is pressed down by thespring to maintain a constant contacting pressure onthe interface of the diffusion couple. All works con­cerning this assembling were carried out in an inert gasatmosphere in a glove box.

A helium gas leak test was carried out for assem­bled capsules by inner pressure method, and the leak­age rate was Jess than 1.0 X 10- 9 Pa m3/s.

The capsules assembled by the above methods wereannealed in a vacuum electric furnace with less than1.3 X 10- 4 Pa. The annealing conditions are 100 and300 h at 400°C, and 100, 300 and 1000 h respectively at600 and Booae. After annealing, the capsules wereopened by a diamond cutter and the specimens (beryl­lium and lithium oxide) were taken out. Following testswere carried out to evaluate the behavior of the con­tacting interface between beryllium and lithium oxide.

Existence of evaporation, transformation or crack

2.2. Capsule

thickness. Their purity is 99.9 wt.%, and the mainimpurities are Ca (0.03 wt.%), Sn (0.007 wt.%), Al(0.003 wt.%) and Si « 0.001 wt.%). Because of theirhygroscopicity, the lithium oxide specimens were han­dled in an inert gas atmosphere.

N. Sakamoto et al. / Compatibility test of Be with Li20160

2 e

Fig. 3. The results of X-ray diffraction on beryllium interfaceannealed at 400, 600 and 800ae for 300 h.

testing temperature range. Becausc of the higher vaporpressure of bcryllium, the evaporated beryllium layerwas formed on lithium oxidc side.

If this phenomenon takc place in a tritium breedingblanket, tritium formed in thc lithium oxide will bereleased through thc evaporated beryllium layer.Therefore, it will be necessary to confirm whether thechemical form of thc releasing tritium is condensed(HTO or TzO) or noncondcnsed (lIT or Tz), andwhether the tritium rclease is protected by the evapo­rated beryllium layer.

-1000

";'

0 •E..,-11 00

..lo!0-

'-'"'" melting point

-1200 • Beo Li

2Be+02c2BeO

-1300500 1000 1500

400"c 600·e 800"C- 900 r-----.:.-r-......~-.-~;---__,

3.3. Lithium-diffusion characteristic into beryllium

formation of low melting point compounds by anneal­ing below 800ae for lOOO h.

T, K

Fig. 5. Standard free energy changes (6.GO) on fonnation forberyllium oxide and lithium oxide.

received

B

A A

AA: Be peak

B: BeO peak

tODD

}1:::===t=-:::::jJ:1,L~==+==tr-2:==::::::j8 00 "C6OO"C

400 "C

10.0

3.2. Identification of reaction products

The results of X-ray diffraction on the berylliuminterface annealed at 400, 600 and 800De for 300 hareshown in fig. 3.

BeO and Li 2 BczO, arc conceivable as reactionproducts, and H. Migge [10] suggested thcir formationprobability. Howcver, as a result of X-ray diffractionon the annealed beryllium interface, Li zBezO, was notidentified in this test. On the other hand, berylliumoxide was identified, and the intensity of the berylliumoxide pcak was the same as for as-received berylliumspecimens. The results of X-ray diffraction before andaftcr ultrasonic washing did not change. From theseresults, it is considered that there is no question about

7Lj ion images on the vertical section of the beryl­liUln interface annealed at 400, 600 and 800ae for 100h arc shown in fig. 4. These images show that thelithium-diffused layer exists at each temperature andthe thickness of the layer increases with increasingannealing temperature. Then, it was obvious that thethickness of the layer increased with increasing anneal­ing time, and that the increase rate of the thicknessdepended on diffusion.

Standard free energy changes (~G(l) on formationfor beryllium oxide [11] and lithium oxide [12] areshown in fig. 5. This figure shows the ~G(l of berylliumoxide is lower than that of lithium oxide at 400, 600and 800ae. This indicates that beryllium oxide is morestable than lithium oxide. Therefore, it is considered

...J

Q)

CO

or-:=========~N

Fig. 4. 7Li ion images on the vertical section of beryllium interface annealed at 400, 600 and 800ae for 100 h.

N. Sakamoto et al. / Compatibility test of Be with Li20

o

161

(a) 400·C

Fig. 6. All ion images hy IMA 011 the vertical section of beryllium interface annealed at 400, 600 and 800°C for lOO h.

that lithium oxide was dcoxidized by bcryllium, andlithium diffused into beryllium. From the viewpoint oftritium release from bcryllium, it will be necessary toinvestigate the effect of thc lithium-diffused layer.

3.4. Oxidation characteristic on beryllium interface

All ion images by IMA on the vertical section ofbelyllium interface annealed at 400, 600 and 800°C for100 h arc shown in fig. 6. Oxidation and collapse onthe beryllium interface have progressed as shown inthis figure. The collapse in this ease is a typical phe­nomenon on beryllium oxidation. Namely, berylliumoxidized preferentially at grain boundary is broken intosmall pieces by intrusion of oxides into beJYllium ma­trix. From this result, it will be neceSS3JY to investigatethc influence of beryllium collapse for the gas sweepblanket.

4. Conclusions

Beryllium is promising as neutron multiplier, con­tacting with lithium oxide, which is candidatc for tri­tium breeding material in a fusion reactor. As the firststep to investigate their compatibility, the diffusioncouple of beJYIIium and lithium oxide was inserted intothe capsule container with high purity helium gas, andthe evaluatiOJl of the chemical interaction on the inter­face was performed after annealing. The informationobtained in this test is as follows.

0) As a result of appearance observation, a layer ofevaporated beryllium was observed on the lithium ox­ide side. However, it is unknown whether the evapo­ratcd bcryllium layer affects the tritium release charac­teristic in lithium oxide or not Therefore, it will be

necessaJY to investigate tritium permeation in such anevaporated belyllium layer.

(2) As a result of X-ray diffraction for evaluation ofreaction products on the beryllium interface, reactionproducts such as Li 2 Be 20 J were not identified in theannealing temperature range 400-800°e. Therefore, itis considered that there is no question about formationof low melting point compounds by annealing belowBOO°e.

(3) A lithium-diffuscd layer existed on berylliuminterface. This phenomenon depended on annealingtemptrature and time. From these results, it will beneeessaJY to investigate the effect of lithium-diffusedlayer on tritium release from beryllium.

(4) Oxidation progressed on beryllium interface, andbeJYllium collapse was observed. From this result, itwill be necessary to investigate the influence of beJYI­Iium collapse for the gas sweep blanket.

Acknowledgements

The authors express their sincere thanks to Dr. Y.Futamura, director of JMTR project and Dr. T. Kura­sawa in Tritium Engineering Laboratory in JAERI fortheir valuable advice to adjust this report. And they arethankful to T. Kikuchi in Mechanical Engineering Divi­sion in JAERI.

References

[1] T. Take.da, H. Amezawa and K. Tobila, JAERI-M 86-(J07(1986).

[2] T. Tone et aI., JAERI-M 87-017 (1987).

162 N Sakamoto et al. / Compatibility test of Be with Li20

[3] S. Mori et a!., JAERI-M 88-014 (1988).[4] Fusion Experimental Reactor Team, JAERI-M 90-090

(1990).[5] H. Kawamura, private communication.[6] A. James Stonehouse, J. Vac. Sci. Techno!. A4(3) (1986)

1163.[7] Y. Ikeda, H. Ito, G. Matsumoto and S. Nasu, Mass

Spectr. 27(4) (1979) 263.[8] H. Kudo, C.H. Wu and H.R. Ihle, J. Nuc!. Mater. 78

(1978) 380.

[9] H. Kimura, M. Asano and K. Kubo, J. Nuc!. Mater. 92(1980) 221.

[10] H. Migge, Proc. 14th Symp. on Fusion Techno!.,Avingnon, 1986, p. 1209.

[11] The Chemical Society of Japan, Kagaku Benran(Handbook of Chemistry) (1984).

[12] O. Gotzmann, J. Nuc!. Mater. 167 (1989) 213.