Low level radioactive waste
Accepted international practice, as outlined in International Atomic Energy Agency (IAEA) guidelines, is that solid low level and short-lived intermediate level radioactive waste is suitable for disposal in near-surface repositories. This type of facility provides the required isolation for this type of waste to decay to acceptable levels of radioactivity within a period of time for which institutional control of the repository can reasonably be expected to continue. The content of long-lived radionuclides in near-surface disposal facility should be less than the limits established by the relevant national regulatory authority.
The operation of near-surface disposal facilities should be consistent with the following IAEA Safety Standards
:
- The principles of radioactive waste management (1995)
- Siting of near-surface disposal facilities (1994)
- Safety assessment for near-surface disposal of radioactive waste (1999)
- Near-surface disposal of radioactive waste: safety requirements (1999).
The IAEA standard Near-surface disposal of radioactive waste: safety requirements sets out the basic requirements that international experience has shown to be necessary for ensuring the safety of near-surface radioactive waste repositories. It covers the requirements relating to protection of human health and the assessment procedures needed to ensure that safety is achieved, as well as a variety of technical requirements. These technical requirements cover such issues as the siting, design, construction, operation and closure of the repository; waste acceptance; and the post-closure phase.
This IAEA standard also provides guidelines for establishing a comprehensive quality assurance program which should be applied to all safety-related activities required for the repository's operation. The quality assurance program ensures that the relevant safety requirements and criteria are met.
The near-surface disposal of low level and short-lived intermediate level radioactive waste has been safely practised for many years in many countries. There are currently more than one hundred repositories for low level waste either operating or being established in more than thirty countries around the world. The UK and other European countries also have near-surface repositories.
Examples of near-surface disposal facilities include:
Intermediate level radioactive waste
Storage in purpose-built stores is an internationally-accepted method of managing intermediate level radioactive waste in the long-term, prior to disposal.
Long-lived intermediate level waste is not suitable for near-surface disposal. Ultimately, it is considered appropriate to dispose of this waste in a geological repository, typically at depths of several hundred metres.
Geological disposal involves the underground emplacement of solid waste in excavations containing an engineered burial system tailored to the disposal site. Disposal in a mined cavity is currently the preferred technique, although deep vertical-bore disposal is being investigated. The basic requirement of any geological formation is its ability to ensure the safety of humans and the environment while also facilitating the safe disposal of the radioactive waste.
The Waste Isolation Pilot Plant (WIPP) in New Mexico, USA, is a disposal facility for long-lived intermediate level waste. WIPP began operating in 1999. It is constructed approximately 600 metres below ground level in a salt formation that is essentially impermeable to water.
High level radioactive waste
A number of countries overseas have high level radioactive waste, which results from the operation of nuclear power reactors and the production of nuclear weapons. Australia has no high level radioactive waste.
After initial storage to allow heat levels to reduce, high level waste can be safely disposed of at depth in stable geological formations. Many countries with high level waste are developing detailed design concepts for disposal facilities and have initiated site-specific repository assessment programs.
Yucca Mountain, approximately 100 miles northwest of Las Vegas, Nevada, USA, is the proposed site for the USA's first geological repository for spent nuclear fuel and high level radioactive waste. The Department of Energy is currently preparing an application to the Nuclear Regulatory Commission for a licence to construct the repository.