Research performed at UNLV on the chemistry of Technetium in

the nuclear fuel cycle

1. Separation U/Tc and synthesis of solids form

2. Synthesis and characterization of Tc-Zr alloys

Background In the US:

Spent fuel inventory in 2014: 65 000 MT of spent fuel ~ 50 MT of 99Tc

DOE: Various options for nuclear waste management

1. Direct disposal of spent fuel: Deep bore hole

2. Reprocessing and development of waste storage forms.

Development of experimental separation process : UREX process: U recovered and Tc placed in a waste form for storage

No PUREX because of proliferation concerns

Study at UNLV focused on Tc separation for UREX process and development of metallic technetium waste form

UREX process: Suite of solvent extractions.

UREX segment

UREX segment

1.5 M H+, 4 M NO3-

Pu, Tc, U, Np

1. Acetohydroxamic acid :AHA Reduction Np, Pu Prevent extraction by TBP

2. TBP in dodecane Extraction: U&Tc

U& Tc TBP/dodecane

3. 0.01 M HNO3

Tc & U back extracted

[U]= 50-100 g/L[Tc] = 60-130 mg/L

0.01 M HNO3

1. U/Tc Separation for UREX processsynthesis of solids forms

Separation U/Tc already been studied at ANL.

Labscale -Demonstration of UREX process using spent fuel Tc separated from U using Anionic exchange resin

No waste Tc form synthesized

Separation U/Tc at ANL: anionic exchange resinSpent fuel

Goal : Separation U/Tc & Synthesis Tc waste form

A- Lab scale demonstration

B- Synthesis and characterization of solid forms

C- Conclusion

Solution: [U]= 100 g/L, [Tc]= 130 mg/L in 1L 0.01M HNO3

Experimental condition:

Elution column: 7 g of treated Reillex

Guard column: 1 g of Reillex

Elution:

-350 ml of 1M NH4OH(flow rate = 4 ml/min)

Set-up for lab scale demonstration

A- Lab scale demonstrationSeparation of Tc from U using anionic exchange resin

Results

Total Sorption yield : 97.7%. Elution yield of treated Resin : 93.7 %

Products obtained after separation

1 liter of UO2(NO3)2 in 0.01M HNO3 350 ml of TcO4- in 1 M NH4OH

Uranium:

0

0.00025

0.0005

0.00075

0.001

0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 2.25 2.5

Volume (L)

mo

les o

f T

c

absorption Washing

elution

Technetium:

Elution profile

2. Filtration

Ammonium Uranyl hydroxide(172.60 g) Tc < DL

Uranyl nitrate

1.Precipitation

NH4OH

Uranyl hydroxide

119.44 g), [Tc] < DL

250 ºC

3 hours

1.Uranium

B- Synthesis of solid forms

1.Synthesis of Uranyl hydroxide

2.Conversion to uranium ammonium oxide

1.Synthesis of (n-Bu4N)TcO4

2.Technetium

NH4TcO4 (15 %)NH4NO3 (85%)

Need to separate!

(n-Bu4N)TcO4: 520 mg

Evaporation

Precipitation(n-Bu4N)HSO4

Centrifugation

2.Conversion to Tc metal (Steam reforming)Reduction at 800 °C under wet Ar: (n-Bu4N)TcO4 + 2H2 → Tc metal + 2 H2O

H2 /CO produced by reaction between Carbone and H2O at 800 °C

T= 800 °C

Wet Ar, 5 hours

Tc metal : 68.2 mg

Arc melting

Dissolution

Tc

XRDTc hexagonal

No other phase

XRD

EXAFS

Tc metal Struct parameter

Scattering C.N. R (Å)

Tc0-TcA 13.6 2.72

Tc0-TcB 4.9 3.85

Tc-TcC 14.7 4.76

EXAFS 13(2) Tc @2.72 Å Tc hexagonal

Characterization Tc metal

Recovering of the Technetium on the guard column by pyrolysis (Steam reforming)

Optical and SEM microscopy

Before pyrolysis

Before pyrolysis

Set up used for pyrolysis

Tc metal: x 40R- TcO4

900 ° C

Wet Ar

Resin in “Tea bag”

Tc metal : SEM x 300

After pyrolysis

After pyrolysis

900 ° C

Wet Ar

1. Optimization Uranium/Technetium separation Tc Elution yield of 93 % on Reillex HP resin

2. Synthesis of U and Tc solid form U product is free of Tc and was recovered in a yield of 99.4%. Tc metal is free of U and was obtained in a yield of 52.5%.

C- Conclusion

2. Synthesis and Characterization of Tc Waste Form

Two metallic waste forms considered:1. Tc metal

Possibility to transmute into stable Ru

2. Tc-Zr alloysMake a combined waste form with the Zr from the cladding

Permit to decrease the melting point of waste form

Determination Tc-Zr phase diagram Stability of Tc-Zr alloys

Reprocessing activity of spent fuel will produce technetium stream DOE: Technetium plan to be incorporated into a metallic waste form

Tc + Zr

Four composition analyzed: Tc6.1Zr, Tc2.1Zr, TcZr1.1, TcZr5.7

Pressed Arc melted Annealed at 1400 °CMixed

Tc6.1Zr Tc2.1Zr TcZr1.1 TcZr5.7

Tc6.2Zr Tc4.6Zr Tc2Zr -Zr(Tc)

Tc2Zr -Zr(Tc) Zr3O

Four different phases observedTc6.2Zr and Tc4.6Zr (-Mn, cubic) Tc2Zr (Zn2Mg, hexagonal)-Zr(Tc) (solid solutions of Tc in Zr)

Tc-Zr alloysSolid-State Structure

P-XRDCompositionSEM

EPMA Tc-Zr alloysSolid-State Structure

P-XRDCompositionSEM

EPMA

Poineau, F., et al. Inorg. Chem. (2010) 49, 1433.

Experimental Tc-Zr phase diagram at 1400 °C

Behavior of Tc-Zr in oxidizing conditions

Tc6Zr, Tc2Z and TcZr treated 3 days at 1500 °C under Ar

Low presence of O2 in the system (release from alumina tube) Zr complete oxidation to ZrO2

Tc remain as the metal

SEM: Phase separation

Dark: ZrO2

TcZr sampleAfter treatment

Light: Tc

Tc metal more stable than Zr toward oxidation

Oxygen free atmosphere required to develop Tc-Zr waste form

Tc metal might be a more stable waste form than Tc-Zr

XRD: Tc metal and ZrO2

Questions