Preparation of the post-operational phase of the Belgian NPPs
Bel V is currently actively working with the licensee Electrabel on the preparation of the post-operational phase of the life of the Belgian NPPs (POP Phase). This phase directly follows the definitive shutdown and aims in a time period of approximately 5 years at evacuating the spent fuels and the operational wastes from the units, and at preparing the dismantling activities. This phase ends when all the spent fuel has been evacuated from the reactor.
This phase is primarily characterized by an evolution of the nuclear island, which is reduced to the SSCs (Structure Systems and Components) needed for ensuring the remaining safety functions, mainly the protection of the spent fuel pools (SFPs). Each system and circuit is subject to an assessment in order to define whether the system remains important to safety and must therefore remain fully submitted to nuclear plant programs (Maintenance, Ageing, Qualification…), is simply functional or can be abandoned during each sub-phase of the POP. Questions arose mainly about the number of trains or the redundancy and diversity of the power sources that are required in order to ensure the safety functions “Decay Heat Removal” and “Confinement” of the spent fuel pools. Bel V is currently working on the assessment of the proposed status of each circuit of the two first reactors to be definitively stopped by the end of 2022 (Doel 3) and in early 2023 (Tihange 2).
In a second step, a status is similarly attributed to each individual component of each circuit, in order to prepare accordingly the required modification files. A downgrading of the status (from “important to safety” to “functional” or “abandoned”) implies a reduction of the plant programs (maintenance, periodical tests, qualification requirements…) applied on this component. As repair and replacement of qualified components gets harder due to supplier and obsolescence issues, it is important to attribute an appropriate status to each SSC for prioritizing and ensuring the safety during the POP.
In parallel to the definition of the nuclear island, the licensee prepares the evacuation of the spent fuels from the SFPs. The spent fuel itself is evacuated after 5 years of decay. During this period, some activities necessary for the complete emptying of the SFPs are performed such as the evacuation of the non-fissile materials from the SFPs, the reparation of the damaged spent fuels or the adaptation of the SFPs to new types of containers. Bel V is currently preparing the assessment of all the modification files required to perform these activities.
Finally, some preparatory activities for the dismantling are also currently prepared by the licensee, the main one being the chemical decontamination of the primary circuit of the reactors. This operation is indeed important for reducing the activity of the pipes, in order to facilitate subsequent dismantling activities. Bel V is currently assessing all the documents justifying this operation.
The preparation of the POP phase is clearly an important challenge for the Belgian Safety Authority in term of workload and planning, as it requires significant evolutions of the nuclear island, the corresponding technical specifications and safety analysis reports of the units, while preparing the emptying of the SFPs.