The 4S (Super-Safe, Small and Simple) reactor is a small fast reactor which has been developed by Toshiba Corporation in cooperation with Central Research Institute of Electric Power Industries (CRIEPI). The 4S system design of the 30MWt version is completed and the licensing activities have commenced. In licensing activities, safety analyses are performed by using Toshiba self-developed safety analysis code SAEMKON (Safety Analysis for Energy, Motion, Kinetics, One dimensional Flow-Network) which is a kind of one dimensional flow network code. To satisfy the regulations of U.S. Nuclear Regulatory Commission, the code verification and validation (V&V) should be performed.

In verification, the equation and coding have been verified through line by line check. In validation, the capability to evaluate particular events has been validated. Among the transient events, Loss of Offsite Power Event (LOSP) is selected as one of the examples for validation in this paper. The validation phase can be classified into 3 phases; Separate Effects Test (SET) phase, Integral Effects Test (IET) phase and Applicability Demonstration phase (confirm that SAEMKON has the capability to analyze particular events).

In SET phase, the analysis results of the important phenomena should be evaluated with using theoretical solutions, other validated computer programs, experimental results, standard problems with known solutions, or published data and correlations. The important phenomena of LOSP are selected by PIRT (Phenomena Identification and Ranking Tables) and the phenomena are classified into 5 types. To validate the code with 5 types of phenomena, various evaluations have been performed with comparison to data of test and published paper.

In IET phase, the test data of EBR-II (Experimental Breeder Reactor-II) are used and the capability of the code to simulate natural circulation behavior of the plant is confirmed.

The applicability demonstration has been also planned by using a CFD 4S full scale model.

In this paper, these validation results of the 4S safety analysis code for LOSP are described.

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