In the process of nuclear power plant design, Pipe Rupture Hazards Analysis (PRHA) was obliged, including postulated rupture location and configurations, jet impingement effects, compartment pressurization effects, environmental influences, flooding effects, leak-before-break and influence on SSC, etc. The analysis of jet impingement is of great importance; aims at obtaining the jet impingement configuration and the impingement force acting on the target. Jet impingement configuration and force depended on the jet flow properties. A jet discharging from a saturated steam line will accelerate and expand due to the pressure differential, and it will partially condense to a low-moisture wet steam with liquid phase in the form of dispersed, entrained water droplets. A jet discharging from a sub-cooled or saturated hot water line (greater than 100°C) would flash to a low quality wet steam and the flashing would cause the jet diameter to expand very rapidly. These jet flows have a phase change and two-phase flow process; the recommended two-phase flow model that should be used was presented in ANSI/ANS 58.2-1988. However, penetration jet impingement which is often encountered in the PRHA was not introduced. In normal cases, the saturated steam, sub-cooled or saturated hot water (greater than 100°C) expands directly to the surroundings. But for penetration jet impingement, the fluid is first discharged to the narrow annular section formed by the pipe and the penetration, then flows through this area, and finally expands to the surroundings at the open side of the penetration. The penetration expanding jet analysis is much more complicated. A method of determining penetration jet impingement in engineering applications was derived based on the fundamental method presented in ANSI/ANS 58.2-1988, Henry and Fauske model recommended. The simplified method took advantage of the two-phase flow models and equations given by ANSI/ANS 58.2-1988; the jet configuration could be calculated effectively and the target impingement force could be derived using the result presented by these equations simultaneously. The impingement pressure field was defined using the program for different initial states of the postulated pipe rupture — namely sub-cooled and saturated. The pressure distribution along the jet centerline obtained has shown clearly the three regions in ANSI/ANS 58.2-1988. The pressure field has shown that sub-cooled water has a larger zone of influence and saturated vapor has a higher mean impingement pressure as Sub-cooled water was under expanded while saturated vapor has higher enthalpy as it contains more energy.

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