This paper presents the results of an experimental model study of the transient loading of steam generator tubes during a postulated main steam line break (MSLB) accident in a nuclear power plant. The problem involves complex transient two-phase flow dynamics and fluid-structural loading processes. A better understanding of this phenomenon will permit the development of improved design tools to ensure steam generator tube integrity. The pressure and temperature were measured upstream and downstream of a sectional model of a tube bundle in cross-flow, and the transient tube loads were directly measured using dynamic piezoelectric load cells. High-speed videos were taken to observe and better understand the flow phenomena causing the tube loading. The working fluid was R-134a and the tube bundle was a normal triangular array with a pitch ratio of 1.36. The flow through the bundle was choked for the majority of the transient. The transient tube loading is explained in terms of the associated fluid mechanics. An empirical model is developed that enables the prediction of the maximum tube loads once the pressure drop is known.

No abstract

A Main-Steam-Line-Break accident in a CANDU nuclear steam generator produces a blowdown in which all the pressurised water is boiled off in a few seconds. The resulting high transient loading on the heat exchanger tubing could lead to their rupture, resulting in the release of radioactive materials out of containment. A better understanding of this phenomenon will permit the development of improved design tools to ensure steam generator safety in the event of such an accident. The paper presents a commissioned experimental rig and instrumentation system, for which a two-phase experimental program has been developed. Using R134a as the working fluid, measurements of temperature, pressure, and tube loading, as well as simultaneous high-speed flow visualisation, have been taken at conditions simulating a full-scale operating steam generator. The experimental results will be used to develop theoretical modelling tools for single and two-phase blowdown, such that an estimate of tube loading during Main-Steam-Line Break can be predicted from initial conditions.

The goal of this research is to improve our understanding of the effects of a postulated Main Steam-Line Break on the transient loading of nuclear steam generator tubes. The analysis of this problem deals with the complex coupling of rapid transient two-phase flow dynamics and fluid-structural loading processes. A main concern of nuclear reactor safety is to ensure that radioactive materials produced by nuclear fission are safely contained. This type of accident produces a ‘blowdown’ in which the pressurised water in the steam generator is boiled off in a few seconds. The resulting transient loading on the steam generator tubing could lead to their rupture, resulting in the release of radioactive materials out of containment. A better understanding of this phenomenon will permit the development of improved design tools to ensure steam generator safety in the event of such an accident. This paper presents a work in progress, describing the purpose-built experimental facility and a summary of commissioning results, including an evaluation of the instrumentation and data collection methodology. The final results of this research will provide physical insights and guidance for the development of predictive modelling tools.

An experimental facility was designed and built to study the loading on steam generator tubes during a blowdown. The facility used refrigerant R-134a and measurements were taken for static and dynamic pressures as well as tube loading and temperatures. Commissioning experiments indicated that the off-the-shelf dynamic pressure transducers and load cells could not take the mechanical and thermal shock loading caused by the blowdown and produced spurious results of no value. This paper presents the instrumentation problems found, explains why they occurred, describes the remedial procedures employed, and outlines the instrumentation validation methodologies developed. The success of the instrumentation development is demonstrated in a series of experiments designed to assess the rapid transient measurement system.