Surveillance schemes that monitor the effect of neutron irradiation on reactor pressure vessel materials employ Charpy impact specimens that are periodically withdrawn and tested as a function of test temperature. The resulting Charpy impact absorbed energy curves have been modeled by a threeparameter relationship with the same functional form as the Burr distribution function. The parameters of the Burr distribution function have been represented as a function of irradiation variables: dose and temperature. The method of maximum likelihood estimation has been used to obtain estimates of model parameters together with their standard errors. A method is presented for the evaluation of uncertainties in Charpy impact energy curves and temperature shifts resulting from irradiation damage. A sampling approach, based on Bayesian inference and employing Markov chain Monte Carlo (MCMC) simulation, has been used to quantify the uncertainties. The main idea of MCMC sampling is to generate the distributions of the model parameters by successive random sampling from the multivariate normal distribution. Illustrative results are presented for irradiated submerged arc weld metal.

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