Acquisition and verification of reference light-water reactor rods

In manufacturing LWR fuel assemblies, the UO2 pellet homogeneity is being tested using a rod scanner device, which is fundamentally intended to detect in very short time (about 1 min) off-specification pellets, i.e. pellets with an enrichment departing x% from the nominal enrichment, the value of x being currently between 10 and 15%. Furthermore, this device is able to verify the 235U content and the weight of the individual rods; therefore, it could be used in nuclear material accountancy, either directly at the rod KMP, or indirectly at the pellet KMP, giving further assurance of the homogeneity of the pellets, or better confidence in the representative sampling. To test the rod scanner device, the operator produces a set of 13 reference rods. It is evident that a high degree of assurance for these reference rods is required, and this is best achieved by collaboration between the operator and the safeguards authorities. Such collaboration was established between the operator, the safeguards authorities (Euratom and IAEA) and nuclear centres (CCR Euratom, Ispra and CEN/SCK Mol), to agree on the way in which characterization should be performed so as to be adequate for both management and verification purposes. Procedures followed by the operator and the safeguards authorities are described. These procedures include: (a) chemical analysis; (b) mass-spectrometric measurements performed by three laboratories; (c) non-destructive measurements of enrichment using NaI and Ge detectors effected by three teams working in plant environment; and (d) surveillance and containment measures. An estimate of the cost for safeguards verification (manpower, samples to be measured, surveillance) is given. (author)