Pore pressure calculation of the UO2 high burnup structure

• Pore pressure is calculated based on local burnup, density and porosity.
• Ronchi's equations of state are used instead of van der Waals’ equation.
• Pore pressure increases as HBS transformation begins and then stays constant.
• A best approximated parameter used for pore pressure calculation is recommended.

UO2 high burnup structure has an important impact on fuel behavior, especially in case of reactivity initiated accident (RIA). Pore relaxation enhances local fuel swelling and puts additional load to the fuel cladding, which makes fuel more susceptible to pellet–cladding mechanical interaction induced failure. Therefore, pore pressure calculation becomes vital when evaluating the fuel failure. In this paper pore pressure is calculated as a function of pellet radial local burnup based on the basic characteristics of HBS using Ronchi's correlation. The results indicate that pore pressure will approach a stable value as HBS is developing. A best approximated C value of 55 N/m is recommended for pore pressure calculation.