Deep borehole disposal as a potential solution for high-level waste (HLW) and spent nuclear fuel (SNF) in Norway – current status and a first generic safety assessment
Authors: Engelhardt Hans-Joachim , Fischer Tilman , Haverkamp Bernt , Wanne Toivo , Wunderlich Ansgar 
Published: September 2023

Abstract. Deep borehole disposal (DBD) is currently being
investigated as a potential solution for the disposal of the existing spent
nuclear fuel (SNF) in Norway. Over the past years, BGE TECHNOLOGY GmbH (BGE
TEC), together with the Finnish companies A-Insinöörit Oy (AINS
Group), Mitta Oy and VTT Technical Research, has supported the Norwegian
agency Norwegian Nuclear Decommissioning (NND) in the development of a deep
borehole concept, including work on different technical details. At the end
of 2022, the consortium was able to win a follow-up contract to further
deepen and advance the work. For this second framework agreement, additional
companies were added to further strengthen the expertise. The Geological Survey
of Finland (GTK), Posiva Solutions Oy (PSOY) and Rambøll are now part of
the new consortium group, which works under the acronym GeoReN (Geological Repositories for Norway). This paper provides an overview of the work carried out in the past for the
deep borehole concept in Norway. In detail, this includes a basic
description of the concept developed for the waste that originates from
different institutions. Initial calculations indicate that a 69 BSK-R canister
may be sufficient for the waste inventory to be considered. As the current
conceptual borehole design provides the basis for most of the other work
carried out, it will be presented and discussed within the paper. Furthermore, as part of the concept development, a first generic
post-closure safety assessment was also performed for the DBD concept. The
main results of the long-term calculations are discussed and presented in
this paper as well. The main objectives of the generic safety assessment
were the identification of critical parameters and assumptions for the model
of the DBD repository and the performance of a first assessment of possible
consequences of the potential post-closure release of radionuclides from the
borehole. To be able to give a prediction at the present stage of the
project, the assessment used conservative assumptions, models and data. The
preliminary results for the normal evolution of the deep borehole repository
indicate that highly mobile radionuclides, such as I-129, Cl-36, Ni-59 and
Se-79, are the major dose contributors and that the expected potential
radiological impact on future generations associated with these releases is
extremely small. In addition, alternative scenarios have been assessed,
which assume a hydraulic gradient leading to advective flow either upward
through the borehole and surrounding excavation damaged zone (EDZ) or between certain parts of the
borehole and the surface via a transmissive fracture system. Despite the
pessimistic assumptions chosen for these scenarios, the maximum dose rates
are significantly lower than the expected regulatory limit. However, it needs to be pointed that the present generic safety assessment
is still on a conceptual level. With more detailed planning and updated
information regarding the inventory, the geological environment, and
the integrity and performance of the engineered barriers, repeated safety
assessments will need to be performed to derive more substantiated results.