Zagreb, Croatia — Successful tests of a promising technology for moving and storing low level radioactive sealed sources are paving the way for a new disposal method for dealing with small volumes of radioactive waste around the world. The method, which involves placing and covering sealed sources in a narrow hole a few hundred metres deep, would allow countries to safely and securely take charge of their own disused radioactive sources. The proof of concept for the technology was tested in Croatia late last year — without the use of actual radioactive material.
Virtually all countries use radioactive sources in health care, industry and other sectors. Many, though, do not have the equipment or staff needed to deal with these once they are no longer usable. Under typical circumstances, a developing country using sealed radioactive sources may generate hundreds of disused sources with low levels of radioactivity over several years, according to IAEA estimates.
“Low activity sources pose the larger challenge because they exist in large quantities around the world and in different forms and variations,” said Andrew Tompkins, a nuclear engineer at the IAEA.
In most developing countries, sealed radioactive sources are stored temporarily. Some developed countries have disposal facilities close to the surface. Both of these pose a security risk if they are not sufficiently protected. The new disposal method represents a long-term solution to this problem that will ultimately help protect people and the environment.
Equipment tests conducted by IAEA engineers and a Croatian radiation protection company confirm the feasibility of a system used to safely move and insert low activity sources as part of borehole disposal.
The tested technology, developed for disused sources with low levels of radioactivity, relies on a robust metal platform and a mobile container called transfer cask, which is used to move the sources into the borehole safely. “It’s simple, affordable and can be deployed worldwide,” said Janos Balla, a waste technology engineer at the IAEA.
“We realized that countries that had low levels of waste, modest infrastructure and limited human and financial resources needed a safe, straightforward and practical solution,” said Balla.
Preventing theft and terrorism
Increasing nuclear security is an important driver behind the development of the new method. “Given that disused sources remain radioactive, we want to limit the probability of these being reached and used for terrorist activities,” said Gert Liebenberg, a nuclear security officer at the IAEA. “Once in the borehole, they are no longer easily accessible to anyone.”
The original borehole idea was developed by the South African Nuclear Energy Corporation (Necsa), and subsequently adapted by the IAEA to incorporate the disposal of sources with higher levels of radioactivity. Today, borehole technical preparations and safety assessments are taking place in several countries, including Malaysia and the Philippines, so that the method can be implemented in the coming years.
The IAEA is ready to train experts in countries interested in using the borehole disposal method and provide them with the necessary assistance, either equipment or technical specifications, to build their own transfer cask. The technology to drill the hole is similar to that used to extract water, and is widely available in most countries, including less developed ones.
Sources: from where to where
Radioactive sources are used widely in medicine and industry, from radiotherapy machines for treating cancer, to industrial tools for sterilizing disposable medical supplies. The most common sealed sources have low levels of radioactivity or a short half-life, meaning they will remain radioactive for only a few months to a few hundred years.
Before disposal, all sources are treated and repackaged through a process called conditioning. When prepared according to this method for disposal, hundreds of sources — the typical amount generated by a developing country each year — take up less than a cubic metre, the size of a small wardrobe.
Once the borehole is in place, the conditioned sources will be loaded into a specially-designed canister, or disposal package, which is then sealed. The sealed canister will then be placed inside the transfer cask and moved over — and eventually into — the borehole.