Preservation of Archaeological Materials in Arid Environments: Analogues Relevant to Yucca Mountain
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Preservation of Archaeological Materials in Arid Environments: Analogues Relevant to Yucca Mountain Neil Chapman1, Amy Dansie2 & Charles McCombie1 1 Independent Consultants, Switzerland ; 2Independent Consultant, USA
ABSTRACT The potential repository at Yucca Mountain in Nevada is in an arid area, in unsaturated volcanic tuff with oxidising conditions, and may be kept open and ventilated for hundreds of years. Existing US work on archaeological material and structural analogues in such conditions has been extended to seek further well-preserved objects in such conditions. The objectives of the study are partly scientific and partly aimed at the public. A wide range of exceptionally wellpreserved glass, metal and organic materials is found in the archaeological record from sites that have been characterised by arid conditions for many thousands of years. Underground preservation environments include those either continuously open (caves) or sealed but not ‘backfilled’ (tombs). Preservation of materials in such openings provides a useful analogue reference point for considering the operation and evolution of the Yucca Mountain repository. INTRODUCTION Archaeological artefacts have been used as analogues of the engineered components of waste repositories in numerous disposal programmes [e.g. 1]. Most attention has been devoted to materials preserved in saturated reducing groundwater conditions, since this is the environment envisaged for repositories in most countries. The potential repository at Yucca Mountain in Nevada is in an arid area, in unsaturated volcanic tuff with oxidising conditions, and may be kept open and ventilated for hundreds of years. It was judged useful to extend existing work on analogues in such conditions [e.g. 2] to seek further relevant, well-preserved objects. This paper discusses some interim findings of an ongoing study supported by the USDOE. Two different aspects of the value of studying the preservation of archaeological artefacts have been recognised. One is scientific, in that corrosion mechanisms and rates may be assessed, or the results of interactions between components over very long times can be observed. The difficulties are that boundary conditions determining behaviour of the objects studied are sometimes poorly known. Second, identifying well preserved archaeological artefacts can enhance public confidence in a safety case. The sometimes intense public and scientific debate about the feasibility of projecting the future behaviour of repository systems over hundreds, thousands or tens of thousands of years can be put into a broader perspective by observing delicate and beautiful artefacts deposited under the ground 2000 to 10,000 years ago. The objectives of the present study are partly scientific, in that objects worthy of detailed, mechanistic examination were sought, and partly aimed at the public, in that the feasibility of preservation of man-made materials for thousands of years should be made as visible as possible. The extensive tunnels that are planned to comprise the
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