Submerged Helium Blower Experience With Specific Reference to the Electro Magnetic Bearing Behaviour on the PBMR Helium Test Facility

The Helium Test Facility (HTF) situated at Pelindaba in the North-West Province of South Africa is one of the test facilities that is owned and operated by the Pebble Bed Modular Reactor (Pty) Ltd. company (PBMR). The main purpose of the HTF is to test the main support systems for PBMR’s demonstration reactor. Helium circulation is achieved with a submerged centrifugal blower making use of electro magnetic bearings. The blower has to circulate helium through the plant at operating pressures ranging from 10 to 90 bar and operating temperatures ranging from ambient to 280 degrees Celsius. This blower has been in operation from 2006 until 2007 when it experienced an electro magnetic bearing failure. Valuable operating experience with this blower was gained. Many lessons on the requirements and operation of such a blower and the plant were learned. This paper presents the operating experience with regard to blower behaviour as well as the behaviour and failure of the electro magnetic bearings. Blower sizing and available pressure ratio is discussed. The problems associated with operation in nitrogen is also discussed. The results of a vibration investigation, that was undertaken to investigate the cause of a high pitched audible noise when the blower was operated at approximately 11,000 r/min, is presented. The electro magnetic bearing failure is discussed with photos presented of the damaged electro magnetic bearing coil. Rust was found inside the blower which is also discussed.