LNG - Nuclear
"Capitalization of operating experience on surveillance and maintenance of buried pipes in several industrial applications", AMP 2010 Workshop, Toronto, Canada, November 2010
Biscons I.(1), Gaine C.(1),Cornish-Bowden I.(1)
The buried assets in the nuclear, oil & gas and water supply industries present differences in their use but some similarities in terms of surveillance and maintenance needs. Regarding the reported events, the Oil & Gas industry is the only industrial field for which the number of buried pipes incidents has not been increasing over the years, even considering corrosion, despite the ageing of pipes. The good results from piping in this field can be related to the by-and-large use of instrumented vehicles (e.g. ultrasonic testing) and potential survey since years ago. Such methods are currently more and more used in the nuclear field even if the techniques are still often in testing.
"Potential contribution of materials investigations in reducing the risks of unavailability of nuclear civil engineering infrastructures", Fontevraud 7, Avignon, France, September 2010
Goy R.(1), Gaine C.(1), Cornish-Bowden I.(1), Auge L.(1), Thillard G.(1), Capra B.(1)
Many consulting assignments undertaken by OXAND within the framework of lifecycle management of existing nuclear civil engineering structures, relied on taking into account the structure’s level of deterioration, the quantitative estimate of its residual strength capacity (obtained by analytical calculations or by computer simulations) and the future progression of this capacity over time. In this context, developments have been made in order to improve the associated methods, based on the latest technical advancements in the assessment of infrastructures.
One of the studied structures, which enters into the framework of these developments, consists of networks of reinforced concrete beams, which are subjected to a rapid increase in their mechanical stresses.
The objective of the study of this structure was to establish an overall diagnosis of the state of the beam networks and of their exploitation, and to identify the main risks associated with the current exploitation of these infrastructures.
The analysis of the structure’s state relied on the periodic inspection reports of the structures, the ageing simulations (carbonation, corrosion) and also on the results of tests and materials investigations.
The diagnosis has highlighted the absence of materials ageing and the good general state of the beams, as well as identified the presence of more frequent and more significant damages localized on the supports.
The diagnosis also confirmed that, in the case of an increase of the mechanical stresses, the risk of a beam failure could be brought under control by setting up a maintenance procedure, which consists in systematically relieving the structure before the overloads reach a limit criterion fixed with ultimate limit state calculations. However, the study showed that this practice could impact the availability of these infrastructures.
Advanced techniques in the assessment of infrastructures, based on enhancing the value of structure materials investigations, represent potential ways to improve the availability rate of the studied infrastructures.
Indeed, several methods exist, which allow to take full advantage of the real performances of the materials, specified through more detailed investigations, in order to refine the structure calculation.
For the studied case, the use of these methods could allow to refine the limit criterion, and thus to have potentially additional strength and availability margins. It consists, for example, in exploiting the potential difference between the structure “such as designed” and “such as built and aged”. Also, the partial safety factors can, for example, be reduced if tests and investigations demonstrate that the real performances of the materials are satisfactory.
"Prediction of prestressing losses for long term operation", AMP 2010 Workshop, Toronto, Canada, November 2010
Cornish-Bowden I.(1), Thillard G.(1), Capra B.(1)
Prestressed concrete is used in nuclear reactor buildings to guarantee containment and structural integrity in case of an accidental event. Experience feedback over 40 years of operation and monitoring has shown that prestressing losses can be much greater than the design estimation with usual standard laws. A method was developed to determine the realistic residual prestress level in structures, in particular for those where no embedded instrumentation was installed, taking into account in situ measurement results rather than design characteristics. The results can enable the owner to justify a lifespan extension while guaranteeing adequate safety.
"Maintenance Optimization through Risk Based Ageing Management Program", CNS 2010, Montreal, Canada, April 2010
Barreau M.(1), Cornish-Bowden I.(1), Augé L.(1), Frenette R.(2)
With increasing demand for energy and the need to control energy costs, many nuclear energy producers choose to extend the lifespan of their existing infrastructures while ensuring operation safety. The success of this decision requires a high level of expertise and know-how in managing the infrastructure life cycle. Oxand has developed and implemented dedicated integrated solutions to assist in managing the ageing of infrastructure over its life-cycle: operation, license renewal application and extended lifespan. These solutions enable to anticipate and optimize the maintenance of the infrastructures thanks to relevant Ageing Management Programs integrating owners’ issues such as safety and availability.
(1)Oxand France, (2)Oxand Canada