The application of the DEM-based burnup construction method in the pebble burnup history analysis in HTR-10

Highlights: • Fuel pebble burnup history is investigated using DEM model of HTR-10. • Correction to Cesium based burnup assay by other radionuclides are discussed. • Activity vector of radioactive isotopes are checked against burnup and times. - Abstract: In the 10 MW high temperature gas-cooled test reactor (HTR-10) operation history, the reactor experienced frequent shutdown periods and irradiation periods with varied power. The complicated operation history is supposed to influence the pebble burnup history. Therefore, this paper firstly introduces a DEM-based pebble burnup tracking method, which combines the DEM pebble flow simulation and the pebble burnup calculation. The method can track the burnup of each pebble in the core individually. Then the method is applied to construct the pebble burnup under the complicated HTR-10 real operation history, and the construction results are analyzed to investigate the influence of operation history on the pebble burnup history. The analyzing results show that the average final pebble burnup at the end of the history is 17–18 GWd/tU. Most of the pebbles experience 2–3 cycles before the reactor finally stops. Moreover, the correlation between the pebble burnup and the Cs-137 activity is found to be influenced by the operation history. The tail of the original single linear distribution turns to be double linear distribution, which brings system error for determining the pebble burnup by Cs-137 activity. In addition, a method that can correct the system error is promised with the help of some recommended auxiliary nuclides.