Ageing surveillance activities

Evidence of ageing problems can appear progressively or suddenly. A rigorous inspection and visual examination plan based on a periodic in-service inspection programme or on a schedule for all selected components and systems should be established. It may also be part of the preventive maintenance programme. Scheduled inspections and visual examinations should be established consistent with the component, system and structure category. Symptoms of ageing related problems are distortion of dimensions, surfaces or materials, leaks, cracks, and even discoloration. Operators and maintenance staff should be 

Inspection activities should also be planned for long maintenance and shutdown periods. They should include manufacturers recommendations for preventive maintenance tasks such as verification of tolerances, lubrications, etc. 

Ageing effects may be detected by a change in measurable parameters. For example, increase in temperature or pressure may be an indication of die accumulation of corrosion products in the tube of a heat-exchanger and instrument drift may be an indication of electronic component degradation. Parameters should be measured periodically in a consistent manner and the readings should be compared and assessed. Physical parameters, such as temperature, pressure, flow rate, control rod drop times, radiation level (e.g. neutron and gamma), water quality, are indicators of the state of a system, structure or component. 

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An epidemiological and statistical method based on linkage of routinely available computerized hospital admission records with vaccination records has been described by Farrington (20). This active surveillance method has been used to assess the attributable risk of convulsions after DTP and MMR immunization and to investigate the relation between MMR vaccine and idiopathic thrombocytopenic purpura in children under 2 years of age in five districts in England. 

The association between Rotarix and intussusception has been studied using case-series and case-control methods in 615 infants with intussusception who were identified through active surveillance at 69 hospitals (16 in Mexico and 53 in Brazil) and in 2050 age-matched infants from the same neighborhood as controls [22 ]. Immunization dates were verified by a review of vaccination cards or clinic records. There was an increased risk of intussusception at 1-7 days after the first dose among infants in Mexico with the use of both the case-series method (incidence ratio =5.3 95% Cl=3.0, 9.3) and the case-control method (OR=5.8 95% CI=2.6, 13). There was no significant risk after the first dose... 

The surveillance requirements should also cover activities to detect ageing and other forms of deterioration due to corrosion, fatigue and other mechanisms. Such activities will include non-destmctive examination of passive systems as well as of systems explicitly covered by limits and conditions for normal operation. If degraded conditions were to be found, then the effect on the operability of systems should be assessed and acted upon. 

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