AN ANALYSIS METHOD FOR THE FUEL-ROD GAP INVENTORY OF UNSTABLE FISSION-PRODUCTS DURING STEADY-STATE OPERATION

An analysis method was developed to predict the equilibrium inventory of unstable fission products present in the fuel-to-cladding gap of fu el elements during steady-state operation. With the shape of grain tre ated as tetrakaidecahedron (TKD), the interlinked fraction of fission gas bubbles to open space at grain corners was determined with use of the Monte Carlo technique and the model of White and Tucker. The metho d was applied to calculate the gap inventory of unstable fission produ cts for CONTACT experiments and FIO series tests. Bubble interlinkage at grain corners was shown to be the rate-controlling step in the rele ase of fission products from the matrix to the open space. Comparison shows that the method reasonably well predicts the gap inventory in th e temperature and burnup ranges investigated.