Improvement of temperature evaluation model of biological shielding concrete for HTTR test simulating LOFC with VCS inactive

Takada, Shoji; Yanagi, Shunki; Iigaki, Kazuhiko ; Shinohara, Masanori ; Tochio, Daisuke ; Shimazaki, Yosuke ; Ono, Masato ; Sawa, Kazuhiro

The VCS of HTTR, which is composed of thermal reflector plates, cooling panel composed of fins connected between adjacent water cooling tubes, removes decay heat from reactor core by thermal radiation, conduction and natural convection in case of LOFC. The metallic supports are embedded in the biological shielding concrete to support the VCS. The LOFC test is planned with the VCS inactive at 9 MWt while the reactor shut-down system disabled. In this test, the temperature distribution in biological shielding concrete is prospected locally higher around the support. A symmetrical model was improved to simulate the heat transfer to the concrete through the VCS support. The numerical results were compared with the measured data acquired from the test, in which the RPV was heated up to around 110 C without nuclear heating with the VCS inactive, to show the temperature is locally high but kept low around the support due to sufficient thermal conductivity to the cold temperature region.