Application of BEPU in review of research reactor safety analysis

To construct and operate a nuclear research reactor, authorization is required to be obtained by the licensee from the Regulatory Body. One of the tasks of the regulatory authority is to verify that the performed Safety Analysis fulfils the safety requirements. Historically, the compliance with safety requirements was assessed using a deterministic approach and conservative assumptions. This provides sufficient safety margins with respect to the licensing limits on boundary and operational conditions. Conservative assumptions were introduced into the framework of the safety analysis to account for the uncertainty associated with lack of knowledge. With the introduction of best estimate computational tools, safety analyses are usually carried out using best estimate approach. Results of such analysis can be accepted by the Regulatory Authority only if appropriate uncertainty evaluation is conducted. Best Estimate (BE) computer codes are capable of providing more realistic information on the status of the plant, allowing the prediction of the real safety margins. The Best Estimate Plus Uncertainty (BEPU) approach has proven to be reliable and providerealistic results if all the conditions are carefully followed. This paper therefore presents the concept of BEPU approach and how it can be applied to research reactors in the safety analysis. The aim of the paper is to investigate unprotected loss-of-flow transients "core blockage" of Miniature Neutron Source Reactor (MNSR) research reactor applying BEPU methodology. The results of the calculations showed that the temperatures in the core are within the safety limits and do not pose any significant threat to the reactor. This paper also discusses the methodology of BEPU approach applied to research reactors to review safety analysis for licensing purposes.