The generation and classification of small leaks in a high pressure water system

This report investigates the detection of small leaks from the primary system of a Nuclear Pressurised Water Reactor. Leak rates of 12 g/s are invariably difficult to detect and locate. The typical leak indicators in a nuclear reactor control room are a drop in pressure and level from the pressuriser, and the air sampler detecting particulate matter. However, in both cases the leak is normally quite substantial by the time any parameters or values are obviously outside the normal operating conditions. Therefore, a small leak could go undetected for a significant amount of time. As part of the reactor safety studies, it is important to have more information about small leaks. Due to the lack of small leak data, the solution was to construct a high pressure water rig producing temperatures and pressures close to those experienced in the primary circuit, these being 200ºC and 100 bar respectively. Pressure is maintained by a vane water pump and heating is achieved by passing a high current through a small diameter, thin walled pipe. To reproduce different size cracks, various size carburettor jets are used. The water on exiting this crack, flashes to steam and immediately meets metallic pipe lagging, which is typical of most primary systems. With the typical crack scenario recreated it is now important to add sensors that will detect conditions associated with a small leak. These sensors are either mounted on or around the lagging material. The parameters that are monitored include vibrations, acoustics, thermal variations, moisture change, air flow and pressure adjustment leaving a predetermined outlet. The sensor outputs are pre-processed and the nonlinear data are applied to an artificial neural network, whereas the other data are applied to a digital logic system. The results showed that with 13 different leak rates, separated by only 1.4 g/s the ANN was able to correctly differentiate and identify different leak sizes with a certainty of over 97%. The results from all the analysis are further presented graphically through an Operator Advisory System. This informs the operator of the predicted leak size and location. All of the available sensor data relevant to the leak can be viewed and location of the leak is presented by a three dimensional model of the reactor system.EThOS - Electronic Theses Online ServiceGBUnited Kingdo