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

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. 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


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 resin

Spent fuel

Goal : Separation U/Tc & Synthesis Tc waste form


A- Lab scale demonstration

B- Synthesis and characterization of solid forms

C- Conclusion


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

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


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


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


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)

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


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%.


2. Synthesis and Characterization of Tc Waste Form


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


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.


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

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


Questions


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