Development of air cooling performance evaluation method for fuel debris on retrieval of Fukushima Daiichi NPS by dry method, 1; Outline of research project

Yoshida, Hiroyuki  ; Uesawa, Shinichiro  ; Yamashita, Susumu   ; Nagase, Fumihisa 

To perform the decommissioning of the TEPCO's Fukushima Daiichi Nuclear Power Station, it is considered that application of four methods (full submersion, submersion, partial submersion and dry methods) to perform fuel debris retrieval from the reactor pressure vessels and the primary containment vessels. In the dry method, the fuel debris is exposed in air, and neither cooling nor filling of water is involved. Therefore, by using this method, the stopping water leakage from the PCV is not necessary. However, evaluation of the cooling performance of air convection for fuel debris is required to perform this method. JAEA starts the research project to develop an evaluation method to estimate the air cooling performance for fuel debris. The evaluation method is developed based on the JUPITER, which has been originally developed to estimate the relocation behavior of melting fuel, in order to estimate the cooling performance by considering the melting fuel debris distribution as initial and boundary conditions. To develop and validate the simulation method for the air cooling of the fuel debris, experimental database is required. Then, a heat-transfer and flow visualization experiment of free and/or mixed convection adjacent to upward-facing horizontal surface is conducted in this research project.