The Rating of Element Closure Welds and Its Influence on Fuel Reliability

Abstract

A high performance standard of CANDU fuel, and similarly of CIRENE fuel is possible only if the frequency of fuel element failures due to incomplete welds is kept very low. Weld rating, i.e. the relative length of sound weld line, is used to characterize the weld completeness. Metallography is used for quantitative determination of the weld rating. The nature of the metallographic inspection method, together with the affordable sample size and the very low acceptable weld failure rate, make a statistical approach to the evaluation of the weld ratings necessary. The paper outlines a statistical method of weld rating assessment. The method links the probability of finding discontinuities in metallographic sections, with the distribution of discontinuities in a statistical sample of welds. It presents the results in the form of a weld rating distribution graph. Applications of the method are discussed. Its use is shown for three batches of CIRENE development welds.