research performed at unlv on the chemistry of technetium in the nuclear fuel cycle 1. separation...
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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 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
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
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
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.
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