ICONE19-44130 DEVELOPMENT OF THE FAST BREEDER REACTOR PLANT DYNAMIC ANALYSIS CODE, ADYTUM

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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. In addition, JNES needs a plant dynamic analysis code has high general versatility and flexibility in preparation for the safety review of a next generation FBR, because we had only specialized analysis code for the MONJU system so far. To fulfill this requirement, JNES has been developing the FBR plant dynamic analysis code (ADYTUM), which has a 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, the ADYTUM code 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. Generally, it is difficult to obtain a good agreement between the measured data in the FBR plants and the computational results, because the plant is extremely complicated and every part of the system influences each other. In order to validate major physical models of ADYTUM, we have tried a method which divides the analysis model into some small regions and we called this method "region dividing method (RDM)" in this paper. The RDM has the following sequences; (1) divides the model into some regions, (2) corrects models and conditions of ADYTUM by comparison between calculated results and test data in each separated region respectively, finally, (3) validates the whole plant system model. We have applied the RDM to the turbine trip test at a 40% power load which was conducted by using the Japanese prototype FBR, MONJU in 1995. After the improving the models and conditions of ADYTUM through the application of RDM, the once through calculation results have shown a good agreement with the test data in the whole plant system.

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