Leapor: A computer code for leakage-rate calculations for cracks in cooling water piping systems

This paper describes the development of a new computer code called Leak Analysis of Piping - Oak Ridge (LEAPOR) which calculates estimates for the leakage rate of water escaping from postulated through-wall cracks in a piping segment of a nuclear power plant cooling water system. The ability of nuclear power plant control and safety systems to detect a piping leak prior to breakage is a fundamental requirement of the leak-before-break concept. The design and assessment of leak-detection systems, therefore, requires the determination of through-wall crack leakage rates covering a significant range of operating and flow conditions. For the primary use case of pressurized water reactors, the coolant is subcooled liquid-phase water at high pressures and temperatures, and the leakage flow regimes can range from adiabatic flow boiling ("flashing") with non-equilibrium vapor generation inside the crack to orifice flow of a subcooled liquid with vapor generation occurring outside of the pipe. The thermohydraulic Henry-Fauske model (with extensions) for non-equilibrium flashing flow through "tight cracks" has been implemented into LEAPOR. A primary driver in the development of LEAPOR has been that its Software Quality Assurance (SQA) requirements included evaluations for correctness, consistency, completeness, accuracy, source code readability, and testability. The new code should be prepared to successfully meet the criteria of formal SQA audits. The attributes of maintainability, portability, and extensibility also informed LEAPOR's layered software architectural design. The paper presents the results of verification and validation studies carried out with LEAPOR where verification by benchmark comparisons to the results of an independently developed leak rate code and validation against experimental data are described.