In this work we introduce the software rPrism, as an branch of the software PRISM model checker, in order to be able to study weighted reactive state transition models. This kind of model gathers together the concepts of reactivity - which consists on the capacity of a state transition model to alter its accessibility relation - and weights, which can be seen as costs, rates, etc.. Given a specific model, the tool performs a simulation based on a Continuous Time Markov Chain. In particular, we show an example of its application for biological systems.