An improved methodology to determine pore size distribution and pore density in the high burnup structure

摘要

The formation of the high burnup structure (HBS) on the peripheral region of the light water reactor (LWR) UO_2 fuel pellet is characterized by a steep increase in porosity. The newly formed micron-size intergranular pores trap most of the created fission gas. The study of the pore size-distribution and its evolution with burnup is fundamental to estimate the fission gas pressure in the pores and can influence the burst release in accidental conditions. Quantitative image analysis is usually employed to quantify the pore size-distribution. It is determined mainly in two-dimension (2D) using a histogram. Few attempts have been made in the past to derive also three-dimensional (3D) pore size-distribution employing the Schwartz-Saltykov (ScSa) method (see Appendix A). In this work, we determine experimentally the pore size-distribution in the HBS and apply a new procedure to determine the distribution, both in 2D and 3D.