When we talk of nuclear waste we imagine spent fuel from nuclear reactors. But many industries and even medical centers produce radioactive waste. What happens to it?
Nuclear waste disposal
There are two approaches to disposal. Dilution and dispersion is used for very low-level radioactive gases and liquids, which are released into the environment and then quickly disperse. Concentration and containment is more relevant to highly radioactive solid waste, which has a long half-life and must therefore be removed from the environment for potentially 1000s of years.
Waste is split into low level, intermediate and high level waste. Low-level waste, which makes up around 90% of radioactive wastecomprises clothing and lab equipment which has been used where radioactive materials are present. Its radiation levels are incredibly low – less than the background radiation emitted by some rocks (e.g. granite). This waste is compacted, put into steel barrels, and then stored in shallow depth concrete-lined vaults.
Intermediate waste (hospital waste comes under this category) is first encapsulated in cement, and then also stored in steel barrels.
High-level waste (HLW) is the stuff that we really need to worry about. This is the spent fuel from nuclear power stations. Although it comprises only 0.1% of nuclear waste, it’s nasty stuff, consisting of spent reactor fuel. It generates a lot of heat and can take hundreds of thousands (even millions) of years to decay. It’s stored in double walled steel containers inside concrete vaults and liquid cooled to prevent overheating. To make the waste easier to handle it can be vitrified – turned into glass – and the majority of HLW undergoes this process.
As yet there is no agreed way to permanently dispose of HLW. All storage facilities are in effect temporary whilst governments try to agree on how to best dispose of it. Various options have been suggest. Shooting it into space has been deemed far too risky – if the rocket exploded before it reached space, HLW would be spread over the entire globe; there’s also a moral issue around using space as a galactic landfill site. Others have suggested keeping it in bunkers as we do now.
However, this stuff will be around for hundreds of thousands of years, and who can say what society will be like in this time? We’re imposing a huge responsibility on future generations by leaving them with this HLW and asking them to look after it.
The view among experts is moving towards deep geologic disposal; in short burying the HLW in deep boreholes sunk in geologically stable zones, the idea being that the waste lies there undisturbed for millennia whilst it quietly decays to safety.
Whilst this idea sounds the most pragmatic and effective, it’s not without its critics. The timescales are immense and we don’t know how the waste containers will hold up over this period. They may fail, leaking HLW into the environment. And no area is truly geologically inactive, there’s always a risk of some movement. And of course there’s the NIMBY (not in my back yard) element – would you want barrels of HLW a mile or so from your home?
Our insatiable desire for energy has left us with a problem that won’t go away for a very long time. Whatever your opinions on nuclear energy, we need it to generate the electricity we use. Alternatives do exist, but at present they can’t generate the amount of power we need. And until they can, we’re stuck with a very unpleasant problem. -MARK LEE