Vitrified forts as anthropogenic analogues for assessment of long-term stability of vitrified waste in natural environments

Abstract

The area's natural analogues, vitrifi ed forts, combustion technology, and vitrifi ed waste have been reviewed. The purpose was to identify if investigations of vitrifi ed rock in hill forts might be warranted for assessing the long-term integrity of vitrifi ed waste in natural environments. Wastes that are being vitrifi ed include ash from incineration of domestic waste, contaminated soil and fi ssion products from reprocessing of spent nuclear fuel. It was found that vitrifi ed materials in at least 200 hill forts constitute good anthropogenic analogues to vitrifi ed waste. The compositions vary considerably from site to site and even within one site and may correspond relatively well to the spans of parameters in the various vitrifi ed wastes. Glasses in vitrifi ed forts compare favourably to archaeological artefacts which are soda-and potash-based and consequently have different corrosion behaviours and may weather too quickly. Natural glasses might be too limited in composition variation and are perhaps also too durable. Combustion technology considerations based on quality of heat analyses indicate that at least some of the vitrifi cations of hill forts were carried out with the specifi c purpose of achieving strong and durable constructions. This makes it considerably easier to envisage how the vitrifi cations might have been carried out, and this, in turn, facilitates comparisons between anthropogenic analogues and modern vitrifi ed wastes.

Vitrified hillforts as anthropogenic analogues for nuclear waste glasses – project planning and initiation

“…Consequently, it has been found pertinent by the US DOE to also include in the objectives to support the understanding of the origin of the samples and their historical context. For instance, there has been a century long debate among historians and archaeologists as to whether the melting of the glass to hold the hillfort rock together was accidental or intentional, and in the latter case whether it was for constructive or destructive purposes [2,6,10,11].…”

“…A recent summary can be found in [13]. It has been found [14,15], see also [2], that there may be at least two main mechanisms that control glass corrosion and thus long-term stability, namely alkali extraction and (congruent) matrix dissolution where the former is favoured by low pH-values and the latter by high. There are also differences between the corrosion of high and low silica glasses [16].…”

“…This has been criticised in view of the contemporary high level of knowledge regarding iron beneficiation and ability to achieve high temperatures by burning charcoal and utilising forced draft [10]. Quality of heat analyses and calculations in [2] regarding wood and charcoal provide further strong support to the conclusions in [10].…”

“…However, hillfort glasses may offer supplementary or even more similar compositions or other characteristics as compared to glasses utilised as analogues previously. [2] A compositional comparison among different glasses is shown in Fig. 1 [3][4][5][6][7][8][9].…”

Compositional Imaging and Analysis of Late Iron Age Glass from the Broborg Vitrified Hillfort, Sweden

“…Swedish hillfort glasses from the Broborg Site near Uppsala, Sweden have recently been proposed as an analogue material to inform long term nuclear waste storage (Fig. 1A) [3]. As part of that effort, a fragment of the Broborg hillfort wall was embedded and polished prior to examination by x-ray methodologies to determine its composition and microstructure (Fig.…”