Complexation of neptunium(V) with fluoride in aqueous solutions at elevated temperatures
Over the past several decades, the production and testing of nuclear weapons in the U.S. have created significant amounts of high-level nuclear wastes (HLW) that are currently stored in underground tanks across the U.S. DOE (Department of Energy) sites. Eventually, the HLW will be made into the waste form and disposed of in geological repositories for HLW. Among the radioactive materials, neptunium is of great concern in the post-closure chemical environment in the repository because of the long half-life of 237Np (2.14•106 years) and the high mobility of Np(V), the most stable oxidation state of neptunium. It is estimated that 237Np, together with 129I and 99Tc, will be the major contributors to the potential total annual dose from the repository beyond 10000 years [1]. Due to the high radiation energy released from the HLW, the postclosure repository is expected to remain at elevated temperatures for thousands of years [1]. If the waste package is breached and becomes in contact with groundwater, neptunium, as well as other radioactive materials will be in aqueous solutions at elevated temperatures. Interactions of radioactive materials with the chemical components in groundwater play an important role in determining their migration in the repository. To predict the migration behavior of neptunium, it is necessary to have sufficient and reliable thermodynamic data on its complexation with the ligands that are present in the groundwater of the repository (e.g., OH–, F–, SO42– ,PO43– and CO32) at elevated temperatures. However, such data are scarce and scattered for 25°C, and nearly nonexistent for elevated temperatures [2]. To provide reliable thermodynamic data, we have conducted investigations of the complexation of actinides, including thorium, uranium, neptunium and plutonium, at elevated temperatures. Thermodynamic parameters, including formation constants, enthalpy and heat capacity of complexation are experimentally determined. This paper summarizes the results of the complexation of Np(V) with fluoride in aqueous solutions at 10–70°C studied by spectrophotometry and microcalorimetry.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 953794
- Report Number(s):
- PNNL-SA-65645; DF0961000; TRN: US1001354
- Journal Information:
- Journal of Thermal Analysis and Calorimetry, 95(2):415-419, Vol. 95, Issue 2; ISSN 1388-6150
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE
ACTINIDES
AQUEOUS SOLUTIONS
ENTHALPY
ENVIRONMENT
FLUORIDES
GROUND WATER
HALF-LIFE
HIGH-LEVEL RADIOACTIVE WASTES
LIGANDS
MIGRATION
MOBILITY
NEPTUNIUM
NUCLEAR WEAPONS
PLUTONIUM
RADIATIONS
RADIOACTIVE MATERIALS
RADIOACTIVE WASTES
SPECIFIC HEAT
SPECTROPHOTOMETRY
TANKS
TESTING
THERMODYNAMICS
THORIUM
UNDERGROUND
URANIUM
US DOE
WASTE FORMS
WASTES