Application of probabilistic modelling to the lifetime management of nuclear boilers in the creep regime: Part 1

Monte Carlo probabilistic simulation has been applied to a large population of nominally identical components in an AGR boiler operating in the creep regime. The components have a history of defectiveness. The R5 procedure is used to calculate creep-fatigue crack growth rates within a probabilistic programme. The inspection process is also modelled probabilistically. The overall result is a ‘prediction’ of past inspection results which can be used to tune the parameters of the model. The model then makes genuine predictions of the required level of remediations in future overhauls by predicting the inspection results. The probabilistic treatment of both the structural calculations and the inspection process jointly has been shown to assist in clarifying the interpretation of the inspections and ascertaining the true state of the plant.

► Creep-fatigue crack growth rate assessments are subject to large uncertainties.
► Difficult in-reactor inspections have limited reproducibility.
► A probabilistic treatment of both assists in ascertaining the true state of the plant.
► Monte Carlo simulations predict the required level of remediation in future overhauls.