ABSTRACT
Experiments on the fuel behavior under the accidents in the High Temperature Engineering Test Reactor (HTTR) design are summarized. For investigating the fission product release from the coated particles under the core heat-up conditions the out-of-pile heating at high temperature ranging from 1400°C to 2200°C was undertaken on the TRISO coated fuel particles irradiated to 1 %FIMA at 1300°C in an in-pile gas loop, OGL-1. During irradiation the fractional releases of the fission gas from the fuel element were determined by measuring the fission gas concentration in the primary loop of OGL-1. The instantaneous reactivity insertion would not be considered in any HTGR designs, but an event due to the reactivity insertion by drawing out the control rods rapidly was predicted in the HTTR design. With respect to the HTTR safety design, following three types of the accident are predicted as phenomena at extreme temperature; core heat-up by loss of forced coolant circulation, coolant channel blockage and rapid reactivity insertion.
