Start-up physics test
Fuel loading to the reactor started in July 1998, and the first criticality was attained on November 10, 1998. Fuels were column-wise loaded from the outer fuel columns to the inner ones and 19 of the total 30 fuel columns made the reactor critical. The first criticality was attained almost in a shape of annular core, installing the outer ring of fuel columns and one inner fuel column leaving the other inner ones filled with dummy fuel blocks. The predicted minimum number of fuel columns attaining the first criticality was 16±1. The discrepancy between the predicted and the measured values was due to impurity and air contents in the dummy fuel blocks used for the calculations. The post calculation with revised graphite block composition showed that the number of critical fuel column is 19. The other inner fuel columns were filled in to give the full core by December 1998. In the course of fuel loading, low power physics tests were carried out for the 21, 24, and 27 fuel columns loaded core. These tests provide useful data for designing future annular cores of advanced HTGRs.