About the project
This webb page is about a development project around the hillfort Broborg. There are two purposes:
1. to contribute to the Swedish cultural heritage by an improved understanding regarding the genesis and function of Broborg
2. to contribute towards a safe disposal of nuclear waste in the USA, and also to the proof of the safety.
____BBroborg is situated about ten kilometers east of Knivsta in the county of Uppland, Sweden. Carbon-14 datings indicate that there have been human activities in the fort during the migration period, but that the fort probably has been abandoned during a long time thereafter. It is overseeing Storån ("the Grand River") which was part of an ancient waterway leading from the Baltic Sea to the inner part of Uppland. It has thus been possible to use the fort for the purpose of control of trade as well as protection against enemies.
___The wall has originally consisted of three parts, and probably also a palisade on top. The upper wall, which has been disintegrated, was a dry wall which might have been held together with a timber construction. The two lower parts, which have constituted some kind of fundament for the upper wall, are still in place and appear to be largely intact. The bottom part of the wall is a dry wall consisting of boulders. The wall in the middle is remarkable since it consists of geniss-like stones which have been joined together by molten rock material. There, the high temperature during the melting has implied that the geniss-like stones have been fire-cracked and thus weakened, and that stones consisting of the rock type amphibolite have molten, expanded somewhat due to some evolution of gas, and solidified to a glass with a high mechanical strength and a good ability to hold the granite-like stones together. It has been concluded in earlier investigations that the vitrification was carried out deliberately and for constructive purposes. However, the question of the reasons for vitrification in ancient hillfort walls has been discussed and argued about among archaeologists for around 200 years, and the debate is still a vivid one.
____In Sweden, the plan is to put the spent nuclear fuel in composite canisters with cast steel on the inside and copper on the outside, and to put these canisters/containers is special holes in crystalline rock at a depth of around 500 meters. It is intended that the space between the canisters and the rock will be filled with compacted bentonite which has a very low hydraulic conductivity. Even if the different components match and support each other in this system, it is nonetheless the canisters that provide the longest and most reliable protection against any release of radionuclides.
____There are different solutions in different countries, and in the USA, part of the spent nuclear fuel has been reprocessed so that the long-lived radionuclides have been concentrated into a slurry. Glass forming elements are to be added to such slurry after which the mixture is turned into a glass by heating. The chemical composition as well as the process have been selected such that the glass becomes very resistant to weathering/corrosion. Extrapolation indicates that the release of radionuclides will be very low even after thousands of years.
____Nonetheless, it is important to relate to reality, i. e. the long-term perspective, and consequently, research has been carried out for decades on analogues, namely natural glass and glass in ancient domestic objets. It is not trivial how such investigations are to be conducted. Natural glasses must be sufficiently resistant in order for them to still be around, but not too resistant, such that they may be too old, in which case it may be difficult to determine the environment that they have experienced. The anthropogenic glasses studied so far, i. e. glass in domestic objects, are more easily weathered as compared to nuclear waste glasses.
____The hillfort glass at Broborg is similar to nuclear waste glass, and it can also be assessed how old it is as well as what environment it has experienced. Therefore, it constitutes a valuable anthropogenic analogue. This has prompted the present research which has been carried out for about two years now in an international co-operation between USA and Sweden. One of the tasks has been the excavation that took place in October 2017 during which a many pristine samples were taken. They are presently being analysed using a number of advanced methods. |
Financing, project management, participants and regulatory authority
The work is financed by United States Department of Energy (US DOE), Office of River Protection (ORP), and the project is managed by Pacific Northwest National Laboratory (PNNL). The work is carried out primarily by the following organisations. In Sweden: the Arkeologists in Uppsala, the Geoarkeological Laboratory, a part of the National Historical Museums in Sweden, and Luleå University of Technology (LTU) / Tekedo AB. In the USA: US DOE ORP, PNNL, United States National Institute of Standards and Technology (NIST), Washington State University (WSU) och Museum Conservation Institute (MCI), a part of the Smithsonian Institution. Permit for the excavation has been granted by the Uppsala County Administrative Board who is also conducting oversight of the work and the reporting. |
