Modeling of the Upper Head of a Pressurized Water Reactor During Transient Operation

A mathematical modeling approach is used to describe the thermal hydraulic behavior of the reactor pressure vessel upper head of a pressurized water reactor. We specifically describe vapor formation in the upper head during a shutdown in the emergency power mode. The multiphase fluid in the upper head is modeled mathematically. Lumped modeling is used, i.e., the properties of the fluid within the head do not vary spatially. Heat transfer occurs between the fluid and the structures, which are also modeled as lumped systems. The ordinary differential equations are solved numerically using standard techniques. The model has been tested and it performs qualitatively as expected. Results show the temporal distribution of temperature, structure heat transfer and void fraction. The model is suitable for different designs of the upper head, including “open dome” and “closed dome”.