Research performed at UNLV on the chemistry of Technetium in the nuclear fuel cycle
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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 99 Tc

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Research performed at UNLV on the chemistry of Technetium in the nuclear fuel cycle

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Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

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


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

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


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

  • 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


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

UREX process: Suite of solvent extractions.

UREX

segment


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

UREX segment

1. Acetohydroxamic acid :AHA

 Reduction Np, Pu

 Prevent extraction by TBP

2. TBP in dodecane

 Extraction: U&Tc

1.5 M H+, 4 M NO3-

Pu, Tc, U, Np

[U]= 50-100 g/L

[Tc] = 60-130 mg/L

0.01 M HNO3

3. 0.01 M HNO3

Tc & U back extracted

U& Tc

TBP/dodecane


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

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


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

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 resin

Spent fuel

Goal : Separation U/Tc & Synthesis Tc waste form


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

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 hno 3

A- Lab scale demonstration

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

Separation of Tc from U using anionic exchange resin

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


Results

Results

Elution profile

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

Products obtained after separation

Uranium:

Technetium:

1 liter of UO2(NO3)2 in 0.01M HNO3

350 ml of TcO4- in 1 M NH4OH


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

B- Synthesis of solid forms

1.Uranium

1.Synthesis of Uranyl hydroxide

1.Precipitation

NH4OH

Uranyl nitrate

Uranyl hydroxide

2. Filtration

2.Conversion to uranium ammonium oxide

250 ºC

3 hours

119.44 g), [Tc] < DL

Ammonium Uranyl hydroxide(172.60 g) Tc < DL


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

2.Technetium

1.Synthesis of (n-Bu4N)TcO4

Dissolution

Evaporation

Precipitation

(n-Bu4N)HSO4

Centrifugation

NH4TcO4 (15 %)

NH4NO3 (85%)

Need to separate!

2.Conversion to Tc metal (Steam reforming)

Tc

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

Arc melting

(n-Bu4N)TcO4: 520 mg

Tc metal : 68.2 mg


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

Characterization Tc metal

XRD

XRD

  • Tc hexagonal

  • No other phase

EXAFS

EXAFS

13(2) Tc @2.72 Å

  • Tc hexagonal


Recovering of the technetium on the guard column by pyrolysis steam reforming

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

Before pyrolysis

After pyrolysis

900 ° C

Wet Ar

Resin in “Tea bag”

Set up used for pyrolysis

Optical and SEM microscopy

Before pyrolysis

After pyrolysis

900 ° C

Wet Ar

Tc metal : SEM x 300

R- TcO4

Tc metal: x 40


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

C- Conclusion

  • 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%.


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

2. Synthesis and Characterization of Tc Waste Form


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

Reprocessing activity of spent fuel will produce technetium stream

DOE: Technetium plan to be incorporated into a metallic waste form

  • Two metallic waste forms considered:

  • 1. Tc metal

  • Possibility to transmute into stable Ru

  • 2. Tc-Zr alloys

  • Make 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


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

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

Arc melted

Annealed at 1400 °C

Mixed

Pressed

Tc + Zr

Four different phases observed

  • Tc6.2Zr and Tc4.6Zr (a-Mn, cubic)

  • Tc2Zr (Zn2Mg, hexagonal)

  • b-Zr(Tc) (solid solutions of Tc in Zr)

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


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

Experimental Tc-Zr phase diagram at 1400 °C


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

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

Dark: ZrO2

Light: Tc

TcZr sample

After treatment

SEM: Phase separation

XRD: Tc metal and ZrO2

  • 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


Research performed at unlv on the chemistry of technetium in the nuclear fuel cycle

Questions


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