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Title: Computational investigations of the speciation of Sr2+ in aqueous solution, and its interactions with the hydrated brucite (0001) surface
Author: Makkos, Eszter
ISNI:       0000 0004 7227 4940
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2017
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The fundamental objective of this research project was to develop a computational model, using high-level quantum chemical techniques based on density functional theory (DFT), which is able to describe the aquo and hydroxide complexes of strontium and their inter- actions with hydrated brucite surfaces, aiming to create a general approach which can be subsequently modified for the investigation of other radioactive ions/surfaces. The first two chapters of this PhD thesis are a general introduction on the project’s industrial relevance and on the computational methodology used. The subject of this study is strongly related to the decommissioning of the UK’s nuclear legacy fuel storage ponds and therefore the the- sis is organised such that, through the three main steps of the computational investigation, it eventually leads to an industrially relevant main conclusion. In the third chapter, the possible strontium hydroxide complexes in aqueous environment have been investigated, in order to establish likely candidate species for the interaction of nu- clear fission-generated strontium with the hydrated brucite surfaces in high pH spent nuclear fuel storage ponds. A combination of the COSMO continuum solvation model and one or two shells of explicit water molecules are employed for describing accurately the hydrolysis of Sr2+. The next chapter presents the periodic electrostatic embedded cluster model, developed for the brucite (0001) surface to be employed in the study of the adsorption reactions. Using the periodic electrostatic embedded cluster method (PEECM), implemented in the TURBOMOLE code, we have created a quantum chemically treated cluster in an infinite array of point charges and validated this surface model by exploring the adsorption of Sr2+ and other s block cations on bare and hydrated surfaces, comparing the PEECM data with those from a periodic DFT study using the CRYSTAL code. In the fifth chapter, the results of the previous two chapters are combined to describe the Sr-surface interactions as realistically as possible. A theoretical reaction was created, in which the energy of the adsorbed Sr2+ ion on a hydrated brucite surface was compared with the energy of a solvated Sr2+ in the bulk solution, i.e. with the previously identified strontium complexes in aqueous phase. To achieve this, the PEECM model was extended with one and two layers of water molecules both in the quantum mechanical and point charge region, whose geometries are based on previous molecular dynamics studies. Several possible complexes are identified both in the presence or absence of solvatedOH− groups with different Sr-surface distances and complex conformation, and their adsorption energies were calculated in order to evaluate the general strength of the possible ion-surface interactions.
Supervisor: Nikolas Kaltsoyannis, P. ; Andrew Kerridge, D. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available