A Study on the Oxidation Behaviorof Uranium

Abstract

The intermetallic compound of aluminum-dispersed UsSi, is used for

Hanaro Reactor(Korea Multipurpose Research Reactor, KMRR) and

U-Zr alloy nuclear fuel is under the development for a Liquid Metal

Reactor in KAERI. Depleted uranium wastes are generated in forms of

chips, scraps and powder during the manufacturing processes of

alloy-type nuclear fuels. As a radioactive waste treatment method has

not yet been fixed for these wastes, they are currently being stored in

a temporary storage house for later treatment. When storing

depleted uranium wastes, careful handling is required due to their very

high oxidation rates.

To determine the oxidation mechanism and the oxidation rate of

depleted uranium wastes, and to find important factors to be considered

in their treatment, an experiment was carried out by varying the

heating rates of an Air-Controlled Oxidizer. The experiment showed

that depleted uranium wastes are pulverized by oxidation because of

the density difference and then converted to U3O8. The grain size of

pulverized powder decreases with increased temperature.

The oxidation rate is different depending on the alloy composition of

the wastes. The oxidation rate of the U~Si alloy waste per unit area

against temperature is as follows :[ -85.8W/>«o/|

dwldt = 6.92 x 106 e\ RT I mg/ cm2 h

That for U-Zr alloy waste is as follows '•I -57.Q2/fe//mo/|

dwl dt = 8.46 x 10 7 e \ RT I mg/ cm2 h

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S.

Table 1. Analysis of impurity content(ppm) in l^Si sample 15

Table 2. Oxidation rates of U-3.9 wt% Si with air 28

Table 3. Program of thermogravimetric analyzer. 37

Table 4. Reaction rate constants for the oxidation of U-10wt% Zr

on air 46

Table 5. Oxdton rates of U-10 wt% Zr in air 47

Table 6. Oxidation rates of UO2 with air 52

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Fig. 1. Microstructure of the specimen before oxidation(x200) 16

Fig. 2. XRD pattern of initial specimen 17

Fig. 3. A Schematic diagram of oxidation test equipment 18

Fig. 4. Shape of a specimen after oxidation at 250°C 21

Fig. 5. Shape of a specimen after oxidation at 275°C 22

Fig. 6. Shape of a specimen after oxidation at 300°C 23

Fig. 7. Shape of a specimen after oxidation at 325°C 24

Fig. 8. XRD pattern change after oxidation of U~Si 26

Fig. 9. Weight gain vs time curve for the oxidation at 250-300°C 29

Fig. 10. Weight gain vs time curve for the oxidation at 325-400°C ••••30

Fig. 11. Rate of weight gain versus 1000/T 31

Fig. 12. Schematic diagram of thermogravimetric analyzer. 36

Fig. 13. Shape of a specimen after oxidation at 350°C 38

Fig. 14. Shape of a specimen after oxidation at 450°C 39

Fig. 15. Shape of a specimen after oxidation at 500°C 40

Fig. 16. XRD pattern change after oxidation of U~Zr 42

Fig. 17. Weight gain vs time curve for the oxidation at 250-300^ 43

Fig. 18. Time dependence of the weight gain at 300-500°C 44

Fig. 19. Rate of weight gain versus 1000/T 45

Fig. 20. Shape of a specimens after oxidation in air 49

Fig. 21. XRD pattern change after oxidation of UO2 50

Fig. 22. Weight gain vs time curve for the oxidation at 300-500T: 53

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Fig. 23. Rate of weight gain versus 1000/T 54

Fig. 24. Shape of DU chips before the oxidation experiment 56

Fig. 25. Shape of samples after oxidation. 58

Fig. 26. XRD pattern change after oxidation. 59

Fig. 27. Weight gain vs time curve for the oxidation at 250-500°C 61

Fig. 28. Rate of weight gain(%) versus 1000/T. 63

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BIBLIOGRAPHIC INFORMATION SHEET

Performing Qrg.Report No.

Sixxisoring Org.Report No. Standard Report No. M S Subject Code

KAERI / TR-987/98

Title/Subtitle

A Study on the Oxidation Behavior of Uranium

Project Manager/Dept.(or Main Author)

Taekook Kim (Rad Waste Treatment Facility Dep.)

Researcher/Dept

Kweonho Kang(RWTF), Kiljeang Kim(RWTF), Dsik Kang(RWTF),Kyung whan Jung(RWTF)

Pub. Place Tae jon Pub. Org. KAERI Pub. Date 1998.3

Page 80 P. HI and Tab. Yes ( v ), No ( ) Size 26 cm.

Note

Classified Open ( v ), Outside ( ), Class Report. TypeTechenical

Report

Sponsoring Org. Contract No.

Abstract

When storing depleted tiranium wastes, careful handling is required due to

their very high oxidation rates.

To determine the oxidation mechanism and oxidation rate of depleted

uranium wastes, the most important factors to be considered in their treatment

, an experiment was carried out by varying the heating rates of the

Air-Controlled Oxidizer. The experiment, showed that depleted uranium

wastes are pulverized after complete oxidation because of the density difference

and then converted to UO2, U3O7, U3O8. The grain size of pulverized powder

decreases with increased temperature.

Subject Keywords

Depleted uranium wastes, Oxidation mechanism, Oxidation rate,Air-Controlled Oxidizer, UO2, U3O3, U-Si. U-Ti alloy.

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