In this paper, the effect is discussed of both pressure and temperature variations and their bearings on the SRA UHB safety factors. A variable peak distribution characterised by probabilities of distinct design and operating conditions is proposed and developed for performing OOS UHB. A routine has been developed recognizing that such a distribution is generally not available in the SRA software. Bearing in mind that friction is an important parameter in the UHB and OOS analysis but not duly considered in the literature to date, an integrated UHB model is introduced in the SRA to account for axial friction. The probabilistic methodology, its implementation and significance are shown through a series of SRA and parametric studies using Monte Carlo simulations. It is demonstrated that a more sensible UHB SRA can be achieved to minimise unnecessary margins, whereby the design parameters can be represented by appropriate probability density functions taking into consideration of maximum design, operating and surge excursion conditions, system availability and reliability levels. Some conclusions and recommendations are presented on the selection of SRA input parameters.

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