The methodology developed provides guidance on the use of Probabilistic Safety Assessment (PSA) for the risk-informed evaluation of Guides which ensure the compliment of Outage Key Safety Functions (OKSFs) in Nuclear Power Plants. The methodology has been applied to the 3rd and 13th Plant Operational States (POSs) as a Pilot experience. These POSs are within the operating mode 4 (Hot Shutdown) of a 3 loops Westinghouse Pressurized Water Reactor. The addressed Guide requires the operability of just one charge pump as boric acid supply source. PSA gives a Core Damage Frequency increase (∆CDF) of 1.19•10 -6 year -1 for the unavailability of the charge pump in standby, consequently, the maximum exposure time (time for the increase of Core Damage Probability of the configuration to reach 1.0E-06) for this situation is T= 53.6 hours. Given an average time for the POSs of 40 hours, it is concluded that the charge pumps requirement is correct. However, it could be improved with the inclusion of an additional inventory replacement function. This would limit the effect on Risk of the charge pump unavailability. Furthermore, the need for the external electrical sources to be available during mode 4 is ratified. The procedure requires the operability of both supply sources during the POSs. The unavailability of one of supply sources them involves a ∆CDF equal to 1.64•10 -5 year -1 and a maximum exposure time of T= 3.89 hours. This requirement is considered appropriate from the risk-informed regulation point of view.

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Aircraft engineering is subjected to many classes of uncertainties due to the lack of proper definition of loads, behaviour of new materials or even due to the inaccuracies produced during manufacturing. Because of that, the most advanced methods of analysis and optimization need to be used during the dimensioning of aircraft structures. One way to increase the safety level of a design could be to increase the safety coefficients for load values or material strength, but this approach would lead to an unacceptable amount of material for the aircraft. More proper approaches can be applied using probabilistic analysis during the design phase. In that case, some of the parameters, such as loads, material properties of manufacturing tolerances are defined as random variables and a probabilistic analysis is carried out to identify the safety of the design. This approach can be also enhanced by introducing the concept of design optimization. In that case the optimum solution for an aircraft structure is obtained even considering the random nature of some of the design variables. In this paper these methodologies will be described and some examples of aircraft structures will be presented to show the potential in real problems.