PSA applications for Research Reactors towards a very low risk

PSA techniques are to be applied for Research Reactors in order to reduce their overall risk. In the present work, a Probabilistic Safety Assessment (PSA) was performed for the Australian Replacement Research Reactor (named OPAL), under contract by Invap. The PSA studies have been performed in parallel with the basic engineering phase of the project. Therefore, preliminary results from "the risk point of view" were used to retrofit the design process, thus permitting improvements to be made to the design of systems and components, and to operating and maintenance procedures. These improvements have resulted in an effective reduction of the residual risk. The overall results of the PSA indicate a very low residual risk for OPAL, and several design characteristics of OPAL contribute to these very low risk estimations. The PSA proved to be a valuable tool to increase the safety level of OPAL, and this was possible because the interaction between the PSA performers and the designers was straightforward all along the development period. The main conclusion is that it is possible to effectively reduce the risk or RRs if the basic design process and the PSA proceed in parallel, eventually converging to a reactor where no external emergency plans are necessary. As many RRs are located close to populated areas, this is a major achieved goal.