Research on the leak-rate characteristics of leak-before-break (LBB) in pressurized water reactor (PWR)

• The leak rate mathematical models of LBB were studied and modified.
• Mathcad programming of leak rate calculation and comparing with experimental data.
• Studies of different initial conditions and friction effect.
• Formed Mathcad code can be used to calculate the crack leak rate accurately.

Leak rate calculation is the foundation of Leak-Before-Break (LBB) technology application in Pressurized Water Reactor (PWR). In the paper, a leak rate Mathcad calculation code with different critical flow mathematical assumptions was completed. The code calculation results were contrasted from the published experimental data. The compared results show that the code calculation results are coincident with experimental data. However, the theoretical results are greater than experimental data with different crack L/D, stagnation pressures and subcooled temperatures in case of ignoring friction effect. While the crack friction effect is considered, the calculated results are well in accordance with the experimental data. Also, the different pressure drops are obtained and studied with variations of important parameters in detail. It demonstrates that the friction effect is a significant factor and must be considered in the crack leak rate calculation. The Mathcad code can be used to calculate the crack leak rate and provide application foundation of LBB in PWR pipe system.