With potential storage of several hundred years underground in a geological disposal facility (GDF) before closure, there is a requirement for radioactive waste packages to perform adequately. Over the past 25 years, cementitous grouts based on blast furnace slag (BFS) and ordinary Portland cement (OPC), have been used in the UK to immobilize intermediate-level waste (ILW), Magnox swarf, and currently such wasteforms are in surface storage awaiting geological disposal. Magnox fuel cladding will slowly corrode when encapsulated in alkaline cementitious grouts to produce hydrogen gas and an expansive corrosion product. Expansive corrosion products may lead to degradation of the wasteform and, if extensive, could affect the container. This study investigated the acute and chronic rates of corrosion of unirradiated Magnox swarf encapsulated in a BFS/OPC grout over a range of temperatures (25, 40, 60, 75 and 90°C) for curing times of up to 2½ years. Structural product degradation starts to develop as the tensile strength of the grout is approached by the expansive forces generated. Deformation of some experimental containers was also noted. An estimate of the time taken for a grouted product to fracture from this study due to the corrosion solely of Magnox is 350 years for storage at 25°C. Although not fully described in this paper, the main cement phases were calcium silicate hydrate, portlandite and gehlenite; the main product of Magnox corrosion was brucite. The curing temperature did not affect the compositions of the Magnox metal, corrosion product or grout.

Irradiation is one of the characteristic conditions that nuclear wasteforms must withstand to assure integrity during their service life. This study investigates gamma irradiation resistance of an early age slag cement-based grout, which is of interest for the nuclear industry as it is internationally used for encapsulation of low and intermediate level radioactive wastes. The slag cement-based grout withstands a gamma irradiation dose of 4.77 MGy over 256 h without reduction in its compressive strength; however, some cracking of irradiated samples was identified. The high strength retention is associated with the fact that the main hydration product forming in this binder, a calcium aluminum silicate hydrate (C–A–S–H) type gel, remains unmodified upon irradiation. Comparison with a heat-treated sample was carried out to identify potential effects of the temperature rise during irradiation exposure. The results suggested that formation of cracks is a combined effect of radiolysis and heating upon irradiation exposure.