Release Characterization of Delayed Neutron Precursors from Breached FBR Fuel Element

抄録

The release behavior of delayed neutron (DN) precursors from the breached fuel was analyzed, based on the diffusional release model. In this analysis, spherical co-ordinate simple approach as well as two-dimensional finite element method were used for the predomiant DN precursor ¹³⁷I.
It was shown that the fuel sodium reaction product (FSRP) layer at the pellet outer surface provided a predominant role for the accelerated release of DN precursors. The macroscopic diffusion coefficient for DN precursors in the FSRP layer was estimated to be 10^-9 to 10^-10m²/s, which is greater than that in unreacted fuel by more than about 10⁶. It was demonstrated that the DN signal response correlated to the growth of the FSRP layer, and did not depend on temperature change of interior fuel itself.