Carbon-14 Source Term – CAST. Progress report for the third year (work at SCK•CEN) (D3.12)

This report describes the progress made at SCK•CEN for the work on Zircaloy-4 in the framework of Work Package 3 of the CAST project. The aim of our work is to investigate the release of 14C from Zircaloy-4 claddings representative for Belgian PWR claddings and the 14C speciation in a cementitious environment, which is relevant for the Belgian Supercontainer design, as perceived for the geological disposal of high level waste. In order to achieve this, we have designed both static and accelerated corrosion tests, and we obtained irradiated material which is representative of commercial fuel cladding. Metallographical analysis was carried out on the unirradiated material, indicating that most of the precipitates in the Zircaloy-4 are Laves phase. The second type of precipitates consist of ZrC, and is elongated, needle-shaped. Measurements were made on the 60Co release from Zircaloy-4, in order to obtain a preliminary estimation of the corrosion rate. However, these measurements were disturbed by precipitation. Furthermore, static and accelerated corrosion test setups were designed. First accelerated tests show a broad passive behaviour of Zircaloy-4.