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Title: Assessment of magnesium potassium phosphate cements for radioactive waste encapsulation
Author: Gardner, Laura Jane
ISNI:       0000 0004 5992 1330
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2016
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In the UK, the current stabilisation/solidification technique for intermediate level waste (ILW) is for encapsulation in a Portland cement (PC) composite, which have desirable physical and chemical interactions with ILWs. However, niche waste streams such as reactive metals are known to corrode in the high pH and high free water environment of PCs. Corrosion can lead to the formation of expansive products and the generation of hydrogen. Consequently, there is a growing demand for tailored encapsulant grouts that can be chosen based on the chemical compatibility with the waste streams. Magnesium potassium phosphate cements (MKPCs) formed via an acid-base reaction, with a near-neutral pH and low water demand are one of the alternative encapsulants under consideration for such niche wastes. The aim of this project was to assess MKPCs for deployment in the nuclear industry with particular focus on: formulation optimisation, chemical stability with wastes, radiation tolerance and performance in accident scenarios, i.e. thermal incident. Uranium corrosion trials revealed a reduced gas generation compared to the standard industry grout. It was also demonstrated that the inclusion of supplementary cementitious materials in MKPCs (to form FA/MKPC and GBFS/MKPC) can lead to the formation of secondary reaction products, likely to be potassium aluminosilicates. The high temperature behaviour (i.e. thermal incident) and the radiation tolerance of blended MKPC binders were chosen to demonstrate the suitability of these binders for the UK nuclear industry. The high temperature performance indicated substantial phase assemblage changes occurred up to 1200 °C, however no cracking or spalling of the pellets exposed to high temperatures was observed, which is an important physical property and could to avoid/limit the radioactivity release in a fire scenario. Whilst, the irradiation experiments (up to 10 MGy) revealed that blended MKPC binders exhibit considerable gamma radiation tolerance (regardless of dose rate). The work demonstrated in this thesis indicates that MKPC binders could be a suitable encapsulant for use in the UK but further work involving scaled up experiments are still needed to provide an in-depth safety case.
Supervisor: Hyatt, N. C. ; Corkhill, C. L. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available