COLLECTION AND ANALYSIS OF COMPONENT FAILURE DATA FROM JET SYSTEMS

Objective of the on going activity is to develop a fusion specific component failure database with data coming from operating experiences gained in various fusion laboratories. The activity started since 2001 with the study of the Joint European Torus (JET) Vacuum (VS) and Active Gas Handling Systems (AGHS). Two years later the Neutral Beam Injectors (NBI) and Power Supply (PS) systems were considered and, in this last year the Ion Cyclotron Resonant Heating (ICRH) system is under evaluation. Number of failures/malfunctions occurred in the years of operations, failure modes and, where possible, causes and consequences of the failures, were identified, as well as whole sets of components which the anomalies are related to. Components were classified and counted in order to find out amount of similar components, related total operating hours and related demands to operate (for components operating in intermittent way). Main reliability parameters (such as failure rate and corresponding standard errors and confidence intervals) associated to the components were estimated too. In this paper results obtained for the NBI and PS will be presented in detail, as well as an overview of the main data estimated for all the systems. As sample of the information that will be reported, we can mention that about one hundred failures were identified since the beginning of operations up to March 2004 for the NBI mechanical components installed in the two NBI boxes. For a NBI Unit of 8 PINIs per Unit, failure rates of 1.7E-4/h of full operating day (16 h/day) and 7.1E-2/h of pulses were estimated, while the failure probability on demand results 7.6E-5/pulse. About 1000 failures and malfunctions were identified in the period January 1997 - May 2003 for the Coil PS systems, while for the NBI PS systems the identified troubles were about 900. Generic malfunctions, such as “Alert Alarm” or “Erratic Alarm” and “Failure to preset” the systems to operate, have been differentiated from troubles related to “Failure to operate” or “Spurious operation” of the systems. When possible, failures of low level components (e.g.: circuit breakers, solid state devices, capacitors, Instrumentation and Control devices, etc.) have been identified by the specific failure modes. It has to be highlighted that component failure rates here evaluated are: • one of the most consistent set of data in the field of fusion facilities, both for amount of components treated and for total number of operating hours; • very useful in support of safety assessment and for availability/reliability analyses of fusion machines/plants