JET operating experience: Global analysis of tritium plant failure

The objective of the activity was to build up an overall data collection about the existing experience on the performances and management of the system dedicated to handle the tritium at the Joint European Torus (JET).At first, the analysis performed in 2002 on data related to JET Active Gas Handling System (AGHS) failures was reviewed considering failures and system updating occurred in the AGHS between 2002 and 2006. Main reliability parameters associated to the components (i.e.: failure rate and the corresponding standard errors and confidence intervals) were estimated by means of investigation on failure modes of components and, where possible, causes and consequences of the failures. About 460 failures/malfunctions on a set of more than 6200 components, operating for about 215,000,000 h, were pointed out since 1995 up to 2006.By the comparison between this statistical assessment and the old one performed in the 2002 it is possible to note, apart few cases, the slight increase of failure rate values because of a slight deterioration of components, due to the ageing. The evaluated failure rates were also compared with failure rates existing in literature for similar applications (e.g.: nuclear power plants, tritium processing laboratories). A good agreement between the values from the different sources came out. Second step of the work was the detailed analysis of some relevant maintenance operations performed to repair significant failures in the plant. Unavailability of components and systems, possible impact on workers’ doses and possible environmental releases related to the maintenance activities were scrutinized. The investigation highlights the very low consequences for workers in terms of doses and the negligible effects on environmental releases. The investigation also highlights essential key elements of procedures undertaken to perform maintenance on the AGHS.