Management of low and intermediate activity nuclear waste
Nuclear waste management is understood as the set of activities that lead to its reuse, its disappearance or its neutralization and evacuation to suitable places. These measures must guarantee long-term security.
Nuclear waste management encompasses all the administrative and technical tasks necessary for the handling, treatment, conditioning, transport and storage of nuclear waste. These actions must take into account both economic and security factors.
Isolation of nuclear waste
The isolation of nuclear waste is done through the interposition of natural and artificial barriers between radioactive waste and human beings, so as to prevent the escape of radionuclides and, therefore, radioactivity, into the environment.
The objective is to suppress all escape routes to the environment, preventing or slowing the migration of radionuclides through groundwater to the surface.
The natural barriers are constituted by diverse geological formations, and the artificial barriers are composed of immobilization matrices, concrete walls and special clays.
The four barriers used to contain radioactive materials are the following:
- Chemical barrier
- Physical barrier
- Engineering barrier
- Geological barrier
The chemical barrier immobilizes the residue in a solid, stable and durable matrix that is chemically inert. This operation is known as conditioning. The most used materials for the matrix are: cement, asphalt and polymers.
The physical barrier is the container where the immobilized nuclear waste is confined, thus avoiding its contact with the outside and the possible dispersion of radioactive material. The containers are metallic drums, resistant to corrosion and with a high conductivity of heat energy that allows the evacuation of residual heat.
The engineering barrier is constituted by structures, armoring and storage systems.
The geological barrier is constituted by the geological formation of the earth's crust where nuclear waste is stored. It must be stable and impermeable, thus stopping the escape of the radioactive elements to the environment in case they overcome the three previous barriers.
Conditioning of nuclear waste
Nuclear waste management is understood as the set of activities that
The conditioning of nuclear waste is constituted by a series of processes. These processes go from the production of the waste, until they are stored in drums, after their treatment and immobilization.
A residue of low and medium radioactive activity can be divided into two parts.
A pare of this nuclear waste is decontaminated, contains almost all the total volume of the original residue and has a low radioactive activity. The other part is a concentration of radioactive material of small volume and with radioactive activity close to that of the original nuclear waste, which is transformed into a solid product, in the case of liquid nuclear waste, or into a compact solid in the case of waste. solid nuclear
The conditioning consists of three phases:
- Main treatment
- Immobilizer and packaging
In the pretreatment, the nuclear waste is classified (according to the activity of its radioactivity, half-life and chemical composition), it is chopped, decontaminated and stored for radioactive decay and transport.
In the main treatment the volume of the nuclear waste is reduced and the nuclear activity is concentrated in said reduced volume. In this way, the storage capacity of the facilities is optimized. In the liquid nuclear waste, the radionuclide is separated from the solution where it is dissolved by chemical precipitation, centrifugation, filtration, evaporation and ion exchange, and is then concentrated. The solid nuclear waste is usually compacted, obtaining small "pills" with enough resistance to prevent its expansion. These pills will be placed in a larger container and immobilized with cement. Radioactive solid organic and biological waste, and combustible liquids will be incinerated, also immobilizing their ashes with cement.
In the immobilization and packaging all the components of the waste are immobilized by means of solidification processes (with cement). In this way, the obtained solid product is chemically inert, resistant to fire, stable against radiation, insoluble to water and conductive of residual heat. The solid product and its container are called packages, and guarantee the immobility of the radionuclides.
Last review: December 19, 2018