Used fuel management strategy in Spain: increase of used fuel storage capacity in Cofrentes NPP

Nuclear Fuel, once its power production stage in the reactor has finished, is stored in used fuel pools (UFPs) in the Nuclear Power Plant (NPP) site for removing the residual heat that produces. From this time, different basic action options exist: - Open cycle: after undefined period of temporary storage (dry/wet storage), used fuel is conditioned and encapsulated for definitive storage as high activity radioactive waste. This option is recognized worldwide as feasible and recommended for nonproliferation issues and less-uncertainty cost estimation alternative. - Closed cycle: after undefined period of temporary storage (dry/wet storage), used fuel reprocessing is proceeded with the object of separating uranium and plutonium from the rest of components for further use in a new nuclear fission process again as fuel. Produced high radioactive wastes are conditioned through vitrification for later handling and final storage. This scheme constitutes a better and more sustainable profiting of nuclear fuel. Closed circle can include separation and transmutation of minority actinides for reducing the activity and radiotoxicity. As main feature, this last option requires the availability of a fleet of fast reactors and industrial separation and transmutation facilities. International consensus exists about the necessity of a Deep Geologic Disposal (DGD) for the final disposal of these wastes, independently of chosen cycle scheme. The basic strategy for used fuel management (UFM) that Spain has selected, so far, is an open cycle scheme, mainly for economic reasons. Conditions that led to take this decision have not changed until nowadays, and are not expected to do, at least in near future. An exaggerated and constant uprise of uranium prices could advice its reconsideration (besides other social and energy political factors). Spanish UFM strategy is established in the Sixth General Radioactive Waste Plan (6. GRWP) and is focused on the centralized interim storage (CIS) of used fuel, based on proved dry storage system technologies, over the time periods required until the definitive or very long term management (DGD). Although the Plan previses the construction of a centralized interim storage, for which a site is being sought, until this facility is commissioned, interim used fuel storage is being safely performed in the NPPs. Two approaches are followed for increasing the used fuel storage capacity in NPPs: i) used fuel pools re-racking, replacing old stainless steel racks by other new high density ones using neutron-absorbing materials, and ii) construction of an Independent Spent Fuel Storage Installation (ISFSI) in the NPP site, based in dry used fuel storage casks technology (metallic or concrete). Cofrentes NPP (BWR-6), totally owned and operated by IBERDROLA, completed a first stage for increasing the storage capacity for irradiated fuel by re-racking of the West UFP of the Fuel Building in past 1997. Nowadays, Cofrentes NPP has recently performed a second stage by re-racking of the East UFP. Initially, both UFP were equipped with storage racks, made of plain austenitic stainless steel. These old racks have been replaced by a design containing a more effective neutron absorbing material that is borated stainless steel (BSS), with the purpose to increase and to optimize (maximize) the storage capacity of the pool. The current project has also included all the modifications in piping and nozzles in the cooling system, which were a prerequisite for the installation of the new storage racks. For execution of the project, interlocks that prevent from transportation of heavy loads over the pool have been removed, and the existing crane has been upgraded as single-failure-proof, according to NUREG-0554 and NUREG-0612 Appendix C. Furthermore, an auxiliary temporary platform has been installed over the pool for making possible different maneuvers. Replaced racks have been decontaminated and stored onsite with adequate provisions according to their remaining activity. (authors)