Nuclear Power
Polymeric encapsulation for radioactive waste immobilisation
Dr Steven Black looks at some of the latest developments to identify optimum methods of encapsulation for a range of waste streams, and the progress being made.
El Dr. Steven Black examina algunos de los más recientes avances para identificar métodos óptimos de encapsulación para distintas corrientes residuales y los avances alcanzados.
Dr. Steven Black untersucht einige der neuesten Entwicklungen, um optimale Methoden der Einkapselung einer Reihe von Abfällen und den dabei gemachten Fortschritt zu ermitteln
C
Fig. 1. Cementation is widely used for encapsulation of radioactive waste (shown here: filters and graphite chunks in a 3m3
box section).
ementation is widely used within the civil nuclear industry worldwide for encapsulation of higher activity wastes (HAW), but some of the waste streams generated by the
industry are difficult to encapsulate using this method. For those waste types, often referred to as WRATS (Wastes Requiring Additional Treatment) or orphan wastes, important strides forward are being made with research by Babcock into various alternative encapsulation materials. In anticipation of the expected requirements for consignment to the UK’s planned geological disposal facility (GDF), immobilisation of nuclear waste in a passively safe and stable form is sought, to prevent the mobilisation of radionuclides in the event of container failure. Te traditional grout mix used for encapsulation, which is based on a mixture of ordinary Portland cement (OPC) with pulverised fly ash (PFA) or blast furnace slag (BFS), provides a good mix of
chemical stability, compatibility with most wastes and well established physical properties, and is relatively cheap with a stable supply base.
Cementation process
Tis formulation is limited in scope, however, for reactive metal wastes and wet wastes where unknown water content and the presence of mobile ions can interfere with the curing process. Te stability of grout-based wasteforms for ion exchange resins, for example, can be affected by leaching during the initial cementation process, resulting in the presence of mobile radionuclides in the grout matrix. Wastes containing metallic aluminium, uranium and magnox cladding may also prove problematic due to potential fracturing of the grout as a result of corrosion of the metals, or hydrogen generation from reaction with the grout, while some waste streams interfere with the cement hydration process and can significantly retard or even prevent curing
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