JRP CALL information
Supported By

European Commission

Short description of the work
The determination of the response of the redox sensitive radionuclides to the evolution of the system containing large amounts of iron and concrete is fundamental to the performance assessment of nuclear waste management systems. Redox transitions in the hyperalkaline pH range of for the radionuclides chosen in this study (Pu(III) ® Pu(IV) at pH+pe ~ –1, U(IV) ® U(VI) at pH+pe ~ +2, Tc(IV) ® Tc(VII) at pH+pe ~ +6) strategically cover the field of stability of the system Fe(0)/Fe(II)/Fe3O4, and thus are expected to provide a key understanding on the interaction of the waste with Fe corrosion products under repository conditions.

All experiments were performed at 22±2°C under inert gas (Ar) atmosphere (O2<5ppm). Batch solubility experiments were performed from undersaturation with a hydrothermally prepared α-Fe3O4(cr). Independent samples were prepared at pHc ~9 and pHc ~13 in 0.1M NaCl-NaOH solutions. Four different redox systems were defined: i. a-Fe3O4(cr) + RN, ii. a-Fe3O4(cr) + Fe(cr) + RN, iii. a-Fe3O4(cr) + 0.01 M SnCl2 + RN and iv. a-Fe3O4(cr) + 0.01 M Na2S2O4 + RN. [RN]0 was in all cases 3×10–5 M. LSC (for Tc-99 and Pu-242) and ICP-MS (for Pu-242 and U-238) were used for the quantification of total concentration. The redox behaviour of these radionuclides in the aqueous phase and on the surface of magnetite was followed in combination with pH and Eh data collected for the same systems. Redox speciation in the aqueous phase was investigated by solvent extraction techniques.

The concentration of Tc decreased steadily from t = 1 day, indicating that Tc(VII) was reduced to Tc(IV) as predicted from thermodynamic calculations. Similar observations were made for Pu, which confirmed in all cases the reduction of the initial +V redox state. The concentration of U decreased in most of the samples below 10–8 M, indicating the reduction to U(IV). However, two of the samples at pHc = 13 and less reducing conditions showed an increased U concentration, confirming the predominance of U(VI).

The experimental results gained within this TALISMAN project are currently being interpreted on the basis of thermodynamic calculations.

Main visitor contact data
Name: Maria Rosa González-Siso Sampedro
Organisation: Amphos 21


JRP Identification
JRP nr: TALI-C02-11
JRP title: Study of redox state of U, Pu, Tc and under highly alkaline conditions in teh presence of iron corrosion products
JRP scope: Scope 3: Actinide materials

Visited Associated Pooled Facility
Visited APF during the stay: KIT-INE - Laboratories
Name of the APF Contact Person: Thorsten Schaefer

Other APF and organisation involved in the JRP
Other organisations involved:
Other APF involved in the project:

Description of the work done at the associated pooled facility
Start date of the stay: 3/1/2014
End date of the stay: 5/31/2014
Quantity of access: 60
Access Unit: Days