Mass spectrometer helium leak testing of large volume pipelines and pressure vessels of a nuclear power plant

In Nuclear Power Plants (NPP) generally the leak tight performance of component/system is checked with appropriate leak testing methods in order to have assurance on their reliability and safe operation during service. Depending on the severity, it implies in the event of failure of the component in service to be leak tight, the leak testing method and the acceptable leak rate is specified. Where radioactive, toxic, inflammable or hazardous operating fluids are involved, even a minute leak from a piping system or a pressure vessel into the environment is a major safety concern. Hence, the components and systems of nuclear power plant are tested thoroughly for their integrity and leak tightness before commissioning into service. Technical specification applicable to liquid sodium service component/system of Fast Breeder Reactors envisage reliable sensitivity for detection of the minutest leaks of the order of 1 × 10 −10 Pa.m 3/s with the help of a mass spectrometer helium leak detector. However, it is difficult to achieve the required sensitivity while testing pipelines with complicated geometry and pressure vessels with large volume. Meticulous planning and preparations are required for conducting such tests. This paper brings out our experience on the successful completion of mass spectrometer leak testing of a piping system including the pressure vessels of an Indian Fast Breeder Test Reactor.