Inhibition of radiation induced dissolution of UO2 by sulfide ― A comparison with the hydrogen effect [1]

Miao Yang, Alexandre Barreiro Fidalgo, Sara Sundin, Mats Jonsson

Division of Applied Physical Chemistry, KTH

September 6, 2013 Roskilde, Denmark

[1] M. Yang, A. B. Fidalgo, S. Sundin, M. Jonsson, J. Nucl. Mater., 434 (2013) 38-42

Outline

Introduction Experimentals Results and discussion Conclusions Acknowledgement

2

Long term safety for Spent Nuclear Fuel Introduction

3

Spent Nuclear Fuel Final Disposal - Deep Geological Repository

Introduction

4

Radiolytical oxidation and its inhibition of UO2

Kinetic of Radiolytical oxdiation of UO2 Inhibition of radiolytical oxidation of UO2

U(IV)

H2O2

2OH-

x HCO3-

UO2(CO3)X(2-2X)(aq)+x H+

H2

2H+

ε

Scheme Processes causing oxidative dissolution of UO2 & Noble metal particle catalyzed H2-inhibition [2]

U(VI)

Introduction

[2] M. Trummer, O. Roth, M. Jonsson, J. Nucl. Mater., 383 (2009) 226-230 5

Motivation

H2S

Reduce H2O2?

Reduce U(VI)?

Poison Pd catalyst?

6

Introduction

Sulfide sources

Bacterial sulfate reduction, BSR, Major source

Thermochemical sulfate reduction, TSR, required 100-140 °C

Dissolution of sulfide minerals, e.g. Pyrite, low solubility in deep repository

Introduction

[3] T. E-L Tullborg, C. J Smellie, G. A-Ch Nilsson, SR-Site sulphide content in the groundwater at Forsmark, TR-10-39 (2010) 45

[3]

7

Infuluence factors

pH and [CO32-] [S2-]

[U(VI)]0=168.3μm, [S2-] T=2.0 mM [U(VI)]0=168.3μm, [CO32-] T=4.0 mM

UO22++HS-↔UO2+S0+H+ [4]

[4] B. Hua, H.F. Xu, J. Terry, B.L. Deng, Environ. Sci. Technol., 40 (2006) 4666-4671

Introduction

8

Pd catalyst poisoning effect

Catalyst

poisoning by

sulfide [5-8]

Competitive adsorption of H2S/HS- with the reactants e.g. UO2

2+ + H2→ UO2 + 2H+

H2S/HS- VS. H2

Modification of the electronic properties of the palladium

in the vicinity of sulfur atoms

Formation of Pd*S compounds (suggested) Pd + H2S(aq) → Pd*S + H2(aq)

Pd + HS-(aq) + H2O ↔ Pd*S + H2(aq) + bOH-

(aq)

[5] L.L. Hegedus, R.W. McCabe, Catalyst Poisoning, (1984) [6] G.D. Angel, J.L. Benitez, Mol. Catal., (1994) 409 [7] S. Wilke, M. Scheffler, Surf. Sci., 329 (1995) 605-610 [8] R. Hughes, Deactivation of Catalysts, (1984)

Introduction

9

Scheme

Effect of sulfide on inhibition of radiation induced dissolution

of UO2

Oxidant(s) scanvenging

H2O2+sulfide

Reduction

Direct reduction N2+U(VI)+sulfide H2+U(VI)+sulfide

Catalytic reduction N2+U(VI)+sulfide+Pd H2+U(VI)+sulfide+Pd

UO2 pellet+sulfide+N2

γ source

Experimentals

10

Methodology

• 3mM H2O2 with 0.1, 0.5, 1 mM H2S/HS-

• [H2O2], Ghormley I3- method [9-11]

• H2O2+2H++2I-→2H2O+I2 • I2+I-→I3-

Oxidant scavenging effect of H2S/HS-

• UO2 pellet, 0, 1, 2 mM H2S/HS- • 137Cs γ-source, dost rate ~0.15 Gy/s • [U(VI)], Arsenazo III method [12,13]

H2S/HS- inhibition of radiation induced dissolution of UO2

• 150 μM U(VI), 0, 1, 2 mM H2S/HS- • Autoclave • [U(VI)], Arsenazo III method

Effects of H2S/HS- on Pd catalyzed reduction of

U(VI) by H2

[9] W.A. Patrik, H.B. Wagner, Anal. Chem., 21 (1949) 1279 [10] T.C.J. Ovenston, W.T. Rees, Analyst, 75 (1950) 204 [11] Y. Nimura, K. Itagaki, K. Nanba, Nippon Suisan Gakk., 58 (1992) 1129 [12] S.B. Savvin, Talanta, 8 (1961) 673 [13] I.K. Kressin, Anal. Chem., (1984) 2269

Experimentals

11

Oxidant scavenging effect of H2S/HS-

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 200 400 600 800 1000 1200 1400 1600 1800

[H2O

2]/m

M

Time/s

0.1mM sulfide 0.5mM sulfide 1mM sulfide

[H2O2]:[H2S/HS-]=~4:1-3:1

[sul

fide]

Figure 1 Concentration of H2O2 plotted against time with different H2S/HS- concentration

Results and discussion

12

In vessel

H2S/HS- inhibition of radiation induced dissolution of UO2 pellet

[sulfide] The inhibition periods for the two sulfide

concentrations used in this work roughly corresponds

to the times required to produce equimolar amounts of

radiolytic oxidants under the present conditions.

0.0

2.0

4.0

6.0

8.0

10.0

0 5000 10000 15000 20000 25000 30000 35000

[U(V

I)]/µ

M

Time/s

without sulfide 1mM sulfide 2mM sulfidePellet in γ-cell

Figure 2 Concentration of UO22+ plotted against irradiation time with different H2S/HS- concentration

Results and discussion

13

Catalytic reduction by H2S/HS- in the presence of N2?

0

20

40

60

80

100

120

140

160

180

0 5000 10000 15000 20000 25000

[U(V

I)]/μ

M

Time/s

N2 N2/H2S N2/H2S added 1mL H2SN2/H2S Readded 1mL H2S N2/H2S/Pd N2/H2S/Pd added 1mL H2SN2/H2S/Pd Readded 1mL H2S

No catalytic effect of Pd on U(VI) reduction by H2S/HS- in the presence of N2

Figure 3 Concentration of U(VI) plotted against reaction time at 1.5 bar N2 under different conditions

Results and discussion

14

In autoclave

Effects of H2S/HS- on Pd catalyzed reduction of U(VI) by H2

0

50

100

150

200

0 10000 20000 30000

[U(V

I)]/μ

M

Time/s

20 bar H2 20 bar H2/H2S(1mM)

20 bar H2/H2S(2mM) 1.5 bar N2/H2S(2mM)

20 bar H2/Pd 20 bar H2/Pd/H2S(1mM)

pH 7.97 7.48 7.87

In autoclave pH 7.74 7.49 7.75

Figure 4 Concentration of U(VI) plotted against reaction time at 20 bar H2 or 1.5 bar N2 under different conditions

Reduction of U(VI) by H2 in the absence of a

catalyst cannot be observed in the given time

period

H2S/HS- reduces U(VI) is strongly pH-dependent

and the rate of reduction increases with increasing

[H2S/HS-] and decreasing pH value

Reduction of sulfide appears to be completely

independent of the presence of H2 in the absence

of a catalyst

No clear poisoning effect can be observed

Results and discussion

15

Conclusions

16

Reduce H2O2? Reduce U(VI)?

Sulfide does reduce H2O2 and U(VI), thereby inhibiting or retarding

radiation induced dissolution of UO2 based spent nuclear fuel.

Poison Pd catalyst?

No evidence of sulfide poisoning of palladium catalyst can be observed in

the present conditions.

Acknowledgement

Special thanks for their remarkable work and kindly help.

Professor Mats Jonsson

Dr. Sara Sundin

Dr. Claudio M. Lousada

Kristina Nilsson

Åsa Björkbacka

Alexandre Barreiro Fidalgo

The Swedish Nuclear Fuel and Waste Management Co., SKB and

China Scholarship Council, CSC are gratefully acknowledged for financial support.

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Thank you for your attention!

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