Understanding Nuclear Waste: Treatment and Safe Disposal
Understanding Radioactive Waste
What is Radioactive Waste?
Radioactive Waste (RW) refers to material containing or contaminated with radioactive nuclei in concentrations higher than those set by authorities, for which there is no provision for later use. It is characterized by its severity and duration.
Types of Radioactive Waste
Waste is categorized based on its half-life (the time required for the number of radioactive atoms to be reduced by half) and specific activity (number of decays per unit time):
- Low and Intermediate-Level Waste: Half-life of less than 30 years.
- High-Level Waste: Half-life of over 30 years, including waste from nuclear weapons.
Ionizing Radiation and Its Impact
Definition and Effects
Ionizing radiation consists of electromagnetic radiation or particles that, originating from a transmission source, spread into space and produce ions when passing through matter. Its effects include the formation of ions and free radicals, which cause chemical reactions with tissue components. This can lead to tumors such as leukemia, lung and skin cancers, and abnormalities in the gonads.
Management in Spain
In Spain, the management of radioactive waste is the responsibility of ENRESA (Empresa Nacional de Residuos Radiactivos S.A.). Historically, storage methods mentioned included ocean dumping for low and intermediate-level waste, and proposals for high-level waste involved launching into space on rockets or burying in ice. (Note: These methods are largely historical or theoretical and not current standard practices.)
Managing Low and Intermediate-Level Waste
Storage and Confinement
Low and intermediate-level radioactive waste is typically confined for a period of 300 years in surface or shallow geological repositories. Waste is often solidified with cement in drums for shipment.
Spain’s El Cabril Facility
In Spain, there is a deposit for these residues in an old abandoned uranium mine in Córdoba. Here, the drums are stored in modules called superficial cells. These cells have a drainage system to control water entry and retain waste.
High-Level Radioactive Waste Treatment
Long-Term Isolation Requirements
It is necessary to ensure the isolation of high-level waste for 1,000 years or more.
Spent Fuel Storage
Spent nuclear fuel is initially stored at power plants in pools, which are concrete structures internally coated with stainless steel sheets. Alternatively, storage containers can be located near the nuclear plant.
Deep Geological Disposal: Multi-Barrier System
The long-term location for this waste would be buried at appropriate locations at depths greater than 300 meters. This is known as deep geological disposal, where four physical barriers are interposed between the waste and the living environment:
- Vitrification of the waste: To prevent leaching.
- Second container: Made of a corrosion-resistant material, designed to confine the solidified residue.
- Waterproof material: Surrounding the container.
- Geological environment: The surrounding rock, with clays often being the most appropriate choice.
Spent Nuclear Fuel Management Alternatives
Open vs. Closed Fuel Cycles
There are two main alternatives for the management of spent fuel from nuclear power plants:
- Open Cycle: Spent fuel is not reprocessed and becomes waste directly.
- Closed Cycle: Spent fuel is reprocessed and can be reused 3 or 4 times.
Reprocessing and Transport Risks
The highest risk activity is considered to be the transport of waste to its final repository, especially prior to conditioning. Conditioned low and intermediate-level nuclear waste is sent to facilities like El Cabril after being cemented and compacted.