Investigation of pressure and temperature variations and flow pattern evolution during pressurized water injected into lead-bismuth eutectic

Steam generator tube rupture is possible to occur in lead-cooled fast reactors due to huge pressure and temperature differences acting on both sides of the tubes. The significant pressure and temperature variations caused by the accident have been experimentally explored, but the tests are extremely sophisticate and only limited information can be measured. Numerical methods are also employed to study the accident yet the water vaporization model was generally over-simplified by ignoring the driven force of pressure. Moreover, the injected medium in most numerical models is water vapor instead of liquid water. A novel transient numerical model for the whole process of pressurized water injection into lead-bismuth eutectic considering pressure-driven water mass transfer is established in this study. The effects of the jet pressure, diameter, and position on the system pressure and lead-bismuth eutectic temperature are investigated from a new perspective of the flow pattern evolution. The pressure and temperature trends in the reactor are found associated with the behavior of the core bubble region formed during the water injection. Steady reactor pressure is determined by the jet pressure under the pressure-driven core bubble expansion. A larger jet diameter leads to shorter core bubble expansion thus reduces the time to achieve steady reactor pressure. Lead-bismuth eutectic gets cooled by the cold core bubble region in a trumpet-shape because of the region's expansion, detachment, and migration.