Radioactive Waste Management and Disposal

Because radioactive waste cannot be chemically treated to remove its hazard, its management is fundamentally a problem of safe, reliable containment and isolation for however long it takes for natural radioactive decay to reduce its activity to an acceptable level -- a period that, depending on the isotopes present, can range from a matter of weeks to many thousands of years. This section covers how radioactive waste is classified and the specific engineering approaches used to manage and dispose of it safely.

Radioactive waste is generally classified into three broad categories according to how radioactive it is and how long it will remain hazardous. Low-level waste includes items such as contaminated protective clothing, tools, and other materials that have been exposed to radiation but carry comparatively low levels of radioactivity and, in many cases, comparatively short-lived isotopes; it can typically be managed through relatively simple measures such as shielded storage for a period followed by disposal as ordinary waste once its activity has decayed sufficiently, or straightforward burial at a licensed low-level waste facility. Intermediate-level waste contains higher levels of radioactivity or longer-lived isotopes -- for example, resins and chemical sludges from reactor operation, or some contaminated reactor components -- and generally requires some form of solidification (for instance, encasing the waste in cement) along with more substantial shielding and more secure storage or disposal than low-level waste. High-level waste is overwhelmingly dominated by spent nuclear fuel and the concentrated liquid waste from reprocessing it; although it makes up only a small fraction of the total volume of radioactive waste generated, it accounts for the great majority of total radioactivity and contains isotopes with half-lives long enough that it must be regarded as hazardous on a timescale of thousands of years, making it the category that demands the most rigorous management.

For high-level waste in particular, two specific techniques are central to safe long-term management. Vitrification is a process in which the radioactive waste, generally in liquid or slurry form, is mixed with glass-forming materials and heated to a very high temperature so that it fuses into a solid block of borosilicate glass, with the radioactive material chemically incorporated into the glass structure itself rather than merely mixed in loosely. This vitrified glass is chemically very stable and highly resistant to leaching, meaning that even if its outer container were eventually to fail, the radioactive material would not readily dissolve out into surrounding water -- a crucial property for a waste form that must remain safely contained for an extremely long period. Deep geological disposal is the complementary long-term disposal strategy: once vitrified (or otherwise conditioned) and sealed within engineered containers, high-level waste is placed deep underground -- typically several hundred metres down -- within carefully selected, geologically stable rock formations chosen for characteristics such as very low permeability and the absence of significant groundwater movement. The logic of deep geological disposal is that, unlike a surface storage facility, which depends on continuous human institutional oversight, maintenance and security to remain safe, a well-chosen deep geological repository relies primarily on passive natural barriers -- the surrounding rock itself -- that do not require ongoing human intervention to continue functioning over the very long timescales involved. …