[en] KBS-3H is a joint project between Svensk Kaernbraenslehantering AB (SKB) in Sweden and Posiva Oy in Finland. The main goal during the project phase Complementary studies of horizontal emplacement KBS-3H 2008-2010 was to develop KBS-3H to such a state that a decision to go ahead with full-scale testing and demonstration could be made. The KBS-3H design is a variant of the KBS-3 method and an alternative to the KBS-3V design. In KBS-3H multiple canisters containing spent nuclear fuel are emplaced in parallel, 100-300 m long, horizontal deposition drifts at a depth of about 400-500 m in the bedrock whereas the KBS-3V design calls for vertical emplacement of the canisters in individual deposition holes. Further development and evaluation of the main KBS-3H design alternatives developed in earlier work, DAWE (Drainage, Artificial Watering and air Evacuation) and STC (Semi Tight Compartments) (Autio el al. 2007) has now enabled a well-founded KBS-3H reference design selection, DAWE has been selected. Regarding long-term safety; bentonite-metal interactions have been in focus and studies have given a good basis for material selection for the Supercontainer, plugs and other supporting structures and titanium is selected. The selections and evaluations made during this project phase will be used in the safety evaluations planned for Forsmark and Olkiluoto in the upcoming project phase. KBS-3H specific production lines have been outlined and layout adaptations for both Forsmark and Olkiluoto have been developed. Full-scale tests of system components have also been carried out with good results; the full-scale compartment plug test shows the ability to install a plug that separates drift compartments hydraulically