Innovative applications of abrasive waterjet for irradiated graphite dismantling and decommissioning

The characterization, dismantling and pre-disposal management of radioactive materials have an important role in safe decommissioning of nuclear facilities. One of the main challenges is related to the management of irradiated graphite (i- graphite) used as moderator and reflector in several nuclear power plants and research reactors. In addition to common radiation protection issues typical of most radioactive waste, easily volatizing long-living radionuclides (above all 3H, 14C, and 36Cl) and stored Wigner energy can be released during imprudent retrieval and processing of i-graphite, that hence require careful considerations and precautions. It is well known that Wigner energy release can be avoided by monitoring the i-graphite temperature, that must be kept below its irradiation temperature, with about 50 °C safety margin. This is especially important for those blocks irradiated below 100 °C. With this regard, among all cutting techniques, the abrasive waterjet (AWJ) can be a promising technical solution that achieves all the thermo-mechanical and radiation protection objectives. In this work, the application of AWJ to segmentation of graphite blocks has been explored, aiming at optimizing the retrieval, storage and disposal of such waste. This would have benefits from the points of view of safety, management, and costs. AWJ technology may represent a valuable alternative to mechanical dismantling techniques from the perspective of following process requirements: — Restraint of suspended dusts; — Low cutting temperature; — Limitation of secondary waste; — Easy remote use; — Low cost. This work was aimed at characterizing the AWJ machining capability of 100x100x600 mm blocks of non-irradiated graphite. Several factorial experiments were designed to optimize the machining process parameters (e.g. traverse speed, abrasive mass flow rate, water pressure). The preliminary results obtained in this work promote AWJ as a valid alternative to other conventional techniques. In particular, secondary waste can be limited by optimizing the abrasive mass flow rate.