The methodology of the study comprised of breaking down the method statement of each removal option into 20-25 sequential activities. For each activity the main hazards were identified, and their probability of occurrence was assessed form detailed technical background documentation and in expert workshop sessions. On this basis a risk model was established using Object Oriented Bayesian Networks, which is a class of probabilistic models well suited for handling interdependent variables. Using this model, the removal options were compared with respect to the technical and personnel risk as well as environmental impact.

The technical feasibility of the removal activities included quantification of major accident probabilities and schedule/ cost problems. These problems could be caused by tool failure or structural condition uncertainty. Personnel safety was evaluated in terms of fatality risk during e.g. diving, cutting or lifting operations.

The main output of the project was a well-documented quantitative basis for selection of the optimal removal option. The study provides high-level decision support based on detailed background technical documentation prepared for the decommissioning project. It included sensitivity analyses and identification of main risk contributors. The study is expected to form an important part of the basis for the public consultation process.