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: MT of spent fuel ~ 50 MT of 99 Tc 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 NO 3 - 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 M HNO 3 Tc & U back extracted [U]= g/L [Tc] = mg/L 0.01 M HNO 3

1. U/Tc Separation for UREX process synthesis 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

Solution: [U]= 100 g/L, [Tc]= 130 mg/L in 1L 0.01M HNO 3 Experimental condition: Elution column: 7 g of treated Reillex Guard column: 1 g of Reillex Elution: -350 ml of 1M NH 4 OH (flow rate = 4 ml/min) Set-up for lab scale demonstration A- Lab scale demonstration Separation 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 UO 2 (NO 3 ) 2 in 0.01M HNO ml of TcO 4 - in 1 M NH 4 OH Uranium:Technetium: Elution profile

2. Filtration Ammonium Uranyl hydroxide( g) Tc < DL Uranyl nitrate 1.Precipitation NH 4 OH Uranyl hydroxide 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-Bu 4 N)TcO 4 2.Technetium NH 4 TcO 4 (15 %) NH 4 NO 3 (85%) Need to separate! (n-Bu 4 N)TcO 4 : 520 mg Evaporation Precipitation (n-Bu 4 N)HSO 4 Centrifugation 2.Conversion to Tc metal (Steam reforming) Reduction at 800 °C under wet Ar: (n-Bu 4 N)TcO 4 + 2H 2 → Tc metal + 2 H 2 O  H 2 /CO produced by reaction between Carbone and H 2 O at 800 °C T= 800 °C Wet Ar, 5 hours Tc metal : 68.2 mg Arc melting Dissolution Tc

XRD  Tc hexagonal  No other phase XRD EXAFS Tc metalStruct parameter ScatteringC.N.R (Å) Tc0-TcA Tc0-TcB Tc-TcC EXAFS 13(2) Å  Tc hexagonal Characterization Tc metal

Recovering of the Technetium on the guard column by pyrolysis (Steam reforming) Optical and SEM microscopy Before pyrolysis Set up used for pyrolysis Tc metal: x 40R- TcO ° C Wet Ar Resin in “Tea bag” Tc metal : SEM x 300 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 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 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: Tc 6.1 Zr, Tc 2.1 Zr, TcZr 1.1, TcZr 5.7 Pressed Arc meltedAnnealed at 1400 °C Mixed Tc 6.1 ZrTc 2.1 ZrTcZr 1.1 TcZr 5.7 Tc 6.2 ZrTc 4.6 ZrTc 2 Zr  -Zr(Tc) Tc 2 Zr  -Zr(Tc) Zr 3 O Four different phases observed  Tc 6.2 Zr and Tc 4.6 Zr (  -Mn, cubic)  Tc 2 Zr (Zn 2 Mg, hexagonal)   -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 Tc 6 Zr, Tc 2 Z and TcZr treated 3 days at 1500 °C under Ar Low presence of O 2 in the system (release from alumina tube)  Zr complete oxidation to ZrO 2  Tc remain as the metal SEM: Phase separation Dark: ZrO 2 TcZr sample After 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 ZrO 2

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