Some JAEA's studies to support development of severe accident analysis for LWRs

Nagase, Fumihisa ; Yoshida, Hiroyuki  ; Kaji, Yoshiyuki  ; Amaya, Masaki  

In order to conduct decommissioning of the Fukushima-Daiichi NPPs properly and reliably, increase of accuracy is required in estimation of the accident progress and status inside the reactors. It is also required to confirm effectiveness of safety features against prevention and mitigation of severe accident (AM) in the existing power reactors. Furthermore, it is necessary to prepare own prediction methods to demonstrate prototypical accident phenomena with higher accuracy. Therefore, Japan Atomic Energy Agency (JAEA) conducts researches and developments in terms of thermal hydraulic behaviour in reactor, fuel damage and degradation process, behaviour of structural materials and pressure vessel, accident analysis, and molten materials relocation in the lower plenum region between lower core plate and lower head in BWRs during severe accidents. The paper presents progresses and recent results of the main research subjects.