High-temperature Drop-solution Calorimetry of PuO2

Xiaofeng Guo1,2, Hakim Boukhalfa2, Jeremy N. Mitchell3, Michael Ramos3, Andrew J. Gaunt4, Robert Roback1, Hongwu Xu1

Motivation of Pu-calorimetry

Transuranium Calorimetry Protocols

• Isoperibol Type, 500~1000 °C

• Determine heats of reactions

• Refractory, volatile-bearing,

air-sensitive, molten-salt, or

variable valence materials can

be studied

• High sensitivity, very small heat effects can be measured

(~0.5 kJ/mol)

• Stable baseline, reproducibility, located in a rad controlled

area (or reactor-house facility)

• Accuracy 1 - 3%

Acknowledgement

• U-, Th-, Np-, Pu-containing solids

• Oxides, silicates, phosphates, etc.

• Actinide-containing minerals

• Chloride-, and fluoride-based molten salts

Interested future systems

High Temperature

Oxide Melt Solution Calorimetry Results and Future Plan Work

Pu serves as an important bridge between the actinides with itinerant and localized 5f electrons. Its unique position may be reflected in its thermodynamic

properties, which can serve as benchmarks for theoretical calculations of actinide behaviour and provide critical parameters for nuclear energy applications,

To ensure a safe and accurate conduct of such calorimetry with minimized risks of contamination, we laid

out a cradle-to-grave protocol for the experiments, including design of a sealed sample dropping device that

can safely contain Pu samples and be incorporated into the high-T calorimeter system.

We obtained the drop solution enthalpy of

PuO2 in molten salt (sodium molybdate) at

700 ℃. This will provide imperative

information for future calorimetric studies

of other Pu-containing phases that are

relevant to nuclear applications.

• Whole setup is

made out of

quartz.

• Reusable in U/Th

experiments) to

minimize waste

process

• Disposable after

each Pu

calorimetry

RT

700 °C

• Use disposable

quartz crucibles to

replace expensive

Pt made

• 3Na2O∙4MoO3

solvent was tested

in quartz crucibles

• Design novel

Hold-and-drop kit

for Pu or other

actinides

experiment

• Provide air-tight

and sealed

mechanism when

drop rad pellets

into the reaction

chamber

Outer Part:

Liner

Middle Part:

Radiation Shield

+

Quartz Crucible

Inner Part:

Pu Dropper

+

Dropping Tube

such as designing new mixed oxide (MOX) nuclear fuels and evaluating the long-term stability of Pu-containing waste forms. However, direct measurements of the thermochemical parameters of Pu-bearing phases,

especially their enthalpies of formations, are largely lacking, which is the motivation of this study. We conducted high-temperature drop-solution calorimetry on PuO2, an important component of MOX fuels.

1 Department of Chemistry and the Alexandra Navrotsky Institute for Experimental Thermodynamics, Washington State University, Pullman WA2 Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos NM3 Materials Science and Technology Division, Los Alamos National Laboratory, Los Alamos NM

4 Chemistry Division, Los Alamos National Laboratory, Los Alamos NM

Actinide Calorimetric Database

drop tube

silica glassliner

sample

solvent

alumina plug

bubbling tubeheaters

insulation

thermopiles

inconel block

voltmeter

Pu Dropper Pu Drop Calorimetry

• Safety documents

• Waste stream approval

• Experiment coordination

• Real-time activity monitor

• Waste disposal

Control team

• Lab arrangement

• Critical designs

• IWD

• Handling samples

• Minimize waste

Calorimetry team

• Sample preparation

• Transuranium

sample transfer

• Sample loading in

rad glove-box

Sample team

16 mg PuO2

93% Pu239, 6% Pu240

Samples were loaded

into the dropper in

the rad glove-box

Droppers were

transferred into the

calorimetry lab

Waste Stream

Enthalpy of drop solution

-46.0 ± 3.8 kJ/mol

AnO2 DHds (kJ/mol)

ThO2 0.89 ± 0.481

UO2 9.49 ± 1.532,3

UO3 -140.40 ± 2.673

NpO2 7.81 ± 1.224

Np2O5 17.11 ± 2.674

PuO2 -46.04 ± 3.75

1. Helean, K.B., Navrotsky, A., Lumpkin, G.R., Colella, M., Lian, J., Ewing, R.C., Ebbinghaus, B., Catalano, J.G., J. Nucl. Mater. 2003, 320, 231-244

2. Helean, K.B., Navrotsky, A., Vance, E.R., Carter, M.L., Ebbinghaus, B., Krikorian, O., Lian, J., Wang, L.M., Catalano, J.G., J. Nucl. Mater. 2002, 303, 226-239

3. Guo, X., Szenknect, S., Mesbah, A., Clavier, N., Poinssot, C., Ushakov, S.V., Curtius, H., Bosbach, D., Ewing, R.C., Burns, P.C., Dacheux, N., Navrotsky, A., PNAS 2015, 112(21), 6551-6555

4. Zhang, L., Dzik, E.A., Sigmon, G.E, Szymanowski, J.E.S., Navrotsky, A., Burns, P.C., J. Nucl. Mater. 2018, 501, 398-403

Reference

Sample

Prep/loading

The obtained drop solution enthalpies of actinide

oxides in sodium molybdate solvent at 700 ℃

Solidified dissolved

sample + solvent

encapsulated in

sealed containers as

LLWRad controlled area

Dropper turn on and off

LA-UR-18-22193

Collaborative team to ensure safety and security Engineer improvement of calorimetric setup