The storage of nuclear waste of low and medium activity is based on the interposition of natural and artificial barriers between said nuclear waste and the environment, so that they are perfectly isolated for the time necessary until their radioactivity decays to harmless levels.
The storage of radioactive waste of low and medium activity is carried out in facilities prepared for it. Most of the waste is cleaning rags, filters and impurities of circuits, ion exchange resins, pieces of facilities, etc., coming from nuclear power plants. Also stored are gloves, syringes, containers, needles, biological waste, etc., generated in hospitals and industries with low or medium radioactivity.
Installations for the storage of nuclear waste
A typical installation of this type is composed of the following buildings and structures:
- Waste Building of Low and Medium Activity: where the tasks of compaction, incineration, etc. are carried out.
- Storage structures of the RBMA: cells aligned in two concourses and in double row where the properly conditioned waste will be placed.
- Quality Verification Laboratory: where the characterization processes are carried out, verification tests and control of the characteristics of the radioactive packages received or conditioned in the installation, and research activities are carried out.
- Service and Control Buildings: constituted by the Transitory Reception Building, Technical Services, Industrial Safety, General Services, Maintenance Workshop, Concrete Container Manufacturing Building and Administration.
The waste to be stored arrives in 220-liter drums transported by trucks authorized for this type of transport and are unloaded in the Transitory Reception Building prior to the Conditioning Building. On this site, the drums are identified and classified into several categories. Afterwards, they are introduced into the containers. In the containers, once the lid is placed, mortar is injected to immobilize its contents.
As a final step in the process, these 24-tonne containers are located within the 28 nuclear waste storage cells. Each storage cell has a capacity for 320 containers. Once each cell is filled, it is closed with a concrete plate that is subsequently waterproofed.
These storage cells are arranged on two platforms of 12 and 16 units respectively. Once completed, the cells will be covered with alternative layers of draining and impermeable materials that will prevent possible infiltrations of rainwater from coming into contact with the nuclear waste, recovering the initial topography.
The infiltration control network has sampling points for the measurement of radioactivity. This network also has a water collection tank. The function of this deposit is to concentrate all the pipes of the nuclear waste storage cells to be controlled and treated if there is any indication of contamination.
To guarantee the minimum environmental impact, there are programs of environmental radiological surveillance. These programs consist in the periodic taking of samples and measurements of radioactivity in air, water, plants and other living beings in the environment, keeping the measured values below those indicated by the current regulations.
Strategies and international systems for storage of low and medium activity waste
For some years, the storage of low-level waste was carried out by discharging into the sea, which is currently totally prohibited in most legislations.
The solution currently valid for the storage of nuclear waste is the final storage on the mainland, where there are two options:
- Surface storage with engineering barriers, as in El Cabril in Spain, with a capacity of 50,000 cubic meters or L'Aube in France, with a capacity of 1,000,000 cubic meters. The purpose of this type of storage is to prevent water, surface or underground, from coming into contact with the drums. Both during the storage phase and afterwards the monitoring of the installation is necessary.
- Underground storage at low or medium depth, such as at the SFR center in Sweden and the Asse mines in Germany. They take advantage of artificial underground mines or galleries. When the storage gallery is full, the entrance tunnels are sealed with bentonite and when all the storage is completed they are sealed to the surface to avoid the possibility of access. The sealed storage does not need any surveillance.