Japan Nuclear Energy Safety Organization, JNES has been studying the methodology to apply the risk informed regulation (RIR) to the safety regulation for Light Water Reactors (LWRs) and Fast Breeder Reactors (FBRs). A best estimate code of plant dynamic analysis is necessary for the RIR application and it must be validated very carefully.

To fulfill this requirement, JNES has been developing a FBR plant dynamic analysis code ADYTUM, which has flexible code structure and algorisms for applying to the safety evaluation. ADYTUM is composed of several inherent components of physical model named “module”, based on one-dimensional flow network model which calculates the sodium flow and the heat transfer between sodium and structures in primary and secondary loop systems. In addition, ADYTUM is designed so that variables of each module have no connection with other modules. Therefore, ADYTUM allows us to calculate and validate each module alone [1].

In order to reinforce the precision of the analysis model of ADYTUM, we are trying to quantify the uncertainty of the model parameters by use of the Code Scaling, Applicability, and Uncertainty (CSAU) methodology for the primary pump stick accident in FBRs. The approaches of the CSAU are (1) to define the physical value and the range of time scale which are focused on, (2) to select the input parameters which have a profound effect on the physical value of focus by use of the phenomena identification and ranking table, and finally (3) to provide the uncertainty quantification of the focusing value.

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