Supply chain disruptions have become key in supply chain management. Supply chain risks do not only emerge from disruptions caused by dramatic incidents or natural disasters. Ordinary, everyday problems provoked by customers and suppliers, or infrastructure and network risks can also affect supply chains. There does not exist decision support tool (DST) to aid managers in decision-making under operational risk. We believe that such a DST should be "user friendly", i.e., the decision maker should be able to easily model his own supply chain using generic and/or specific modules and functions available in the tool. In order to attain this goal, the first step is to provide a detailed specification for the above mentioned DST. More specifically, we need to identify the parameters af a supply chain that need to be considered in the generic modules of the DST and the risk categories that should be taken into account by the DST. The current article aims at providing an answer to these questions. To this end, we provide a taxonomy of supply chain risk classes. This taxonomy is based on an extensive literature review in order to broaden the already existing risk taxonomies. We propose a SysML based model to link the supply chain structure and the risk classes previously described. This SysML model gives the basic specifications of the DST.