Experimental studies in the EAGLE-3 project for controlled material relocation in severe accidents of sodium-cooled fast reactors

加藤 慎也; 松場 賢一; 神山 健司; Mukhamedov, N.*; Akayev, A.*; Pakhnits, A.*; Vurim, A.*; Baklanov, V.*

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To achieve the In-Vessel Retention (IVR) in case of Core Disruptive Accidents (CDAs) is of prime importance in enhancing safety of sodium-cooled fast reactors (SFRs). In order to ensure IVR, we are investigating the feasibility of the controlled material relocation (CMR) which enables to decrease the reactivity of degraded core and encourage cooling of relocated material. EAGLE-1 and -2, which have already conducted as the collaboration studies of Japan Atomic Energy Agency (JAEA) and the National Nuclear Center of the Republic of Kazakhstan (NNR-RK), focused on the molten-fuel discharge on the early phase of CDAs and demonstrated the molten-material discharge through the intra-subassembly sodium-filled duct without an inner structure1). In EAGLE-3, the discharge of molten-core material, which gradually expands in the core region by decay heat during the later phase of CDAs, toward the lower sodium plenum through the control rod guide tubes (CRGTs) has been focused. CRGTs have internal structures, such as a sodium-flow regulator, which could affect fuel discharge. Thus, in order to clarify the effect of the internal structures in the CRGT on the discharge behavior of the molten-core material, a series of experiments has been conducted. The knowledge obtained through the EAGLE-3 experiments are presented here.