Prediction of fuel performance and fission gas release behavior during normal operation of the high temperature engineering test reactor by JAERI andFZJ modeling approach

In high temperature gas-cooled reactors (HTGRs), coated fuel particles are employed as fuel to permit high outlet coolant temperature. The essential f eature of HTGRs is the role of the coated fuel particles acting as tiny con tainment and the principal barrier against radionuclide release under any o perational and accident condition. For a safe operation of the High Tempera ture Engineering Test Reactor (HTTR), the continuous and reliable measureme nt of the coolant activity is required to allow an evaluation of the fuel p erformance and the radiological assessment of the plant during normal opera tion conditions. Since fission gases do not plateout on the inner surface o f the primary cooling system, their concentrations in the primary coolant r eflect the core-average through-coatings failure fraction and the fuel matr ix contamination fraction. The main purpose of this report was to give a pr ediction of the fuel performance and fission product behavior in the HTTR u nder normal operating conditions by applying the calculation models as used at Japan Atomic Energy Research Institute and Research Center Juelich (FZJ ), Germany, and to compare the results and methodologies. In the prediction of core average failure fraction, JAERI model gave much earlier failure an d about two times larger than FZJ model. In the fission gas release predict ion, FZJ model showed later increase of fractional release than JAERI model and rapidly increased towards the end of the operation.