Nuclear waste management

 Created on Friday 06 Feb 2009
by Χριστίνα Μελίδου

christina_melidou's picture
Pin It
1232
vote

Spent nuclear fuel stored underwater and uncappedA big concern when it comes to nuclear power plants is waste management. What do you do with all the stuff that's no longer useful but is still radioactive? Well, first of all let me start by saying that, contrary to what happens in other industry sectors, nuclear power plants are obliged by law to handle their own waste. And when it comes to waste management there are two factors one needs to consider: quantity - how much waste is actually produced, and quality - what kind of waste.
Regarding the actual amount of radioactive waste, let me give you some figures provided by the World Nuclear Association:

  1. In countries that have nuclear power plants in operation, radioactive waste comprises just 1% of total industrial toxic waste.
  2. In the U.K., it has been estimated that radioactive waste represents a volume of 840cm3 per person per year - less than the volume of two videotapes.
  3. Finally, according to the French Atomic Energy Commission radioactive waste in France is less than a kilogram per person per year. This becomes even more important when we take into account that France has the highest percentage of electricity produced by nuclear power plants in the world. 

But, even though numbers prove that the quantity of radioactive waste is not substantial, people are understandably concerned about waste from nuclear power plants because after all it is "radioactive". This brings me to the second factor: the kind of radioactive waste produced. The International Atomic Energy Agency has divided radioactive waste in four groups taking into consideration various criteria, such as concentration of radionuclides, heat content etc. The first category is exempt waste. Exempt waste has such a low concentration of radionuclides that it's basically not considered radioactive and need not be handled with any special care. The second category is low level waste which contains small amounts of mostly short-lived radionuclides Things that could fall in this category include, for example, clothes, paper or filters that have been inside the nuclear power plant. The best option for disposing of exempt and low level waste is burial in shallow landfill sites, that is burying them close to the surface, which is what most european countries do with their domestic waste as well. In fact, the main concern with these first two categories is not radioactivity, which is low, but actual volume so in many cases the waste is incinerated or compacted prior to disposal so that it takes up less space.

The real radiological threat could, in theory, come from the next two categories, intermediate and high level waste. By intermediate level waste we usually refer to parts of the actual reactor (concrete, pipes etc), which have become activated because they have been in the reactor for a long time. High level waste refers to the spent fuel itself, which contains fission products and transuranic elements. The first question that arises when we get our hands on this material is: is it really waste? The answer is that at least part of the spent fuel can be recycled. You can reprocess it to extract uranium and plutonium, which can then be reused in the reactor. What's left after reprocessing is really waste for our generation. And I am saying "our generation" because future generations could find some other use for it. So, from that point on, we need to ensure that this material remains isolated from the biosphere until it's safe. The first step is allowing a cooling period because this material, apart from being radioactive, is also very hot. So you keep it in artificial ponds or in ventilated rooms (usually inside the npp) and you allow a period of 30-50 years for it to cool down. This has an added bonus because while the material cools, it also decays so that by the end of the cooling period it only has about a thousandth of its original radioactivity left. Still, you can't just ignore it. The second step is immobilising the waste. You incorporate it in something like borosilicate glass, which is what we call pyrex glass, to make it solid. The third step is putting this solid piece of waste in metal containers. They can be made out of stainless steel or copper and they sometimes have an extra coat of bentonite clay to make them impermeable by water. The final step, which is deciding what to do with the metal containers, has not been implemented yet but there is almost universal consensus that the best option is deep geologic burial, in simple terms you bury it deep underground.

The repository at the Olkiluoto Nuclear Power Plant in Finland

One european country with two nuclear power plants and a strong environmental policy has already started building its burial site. It is Finland and their efforts have been publicised through research*eu, which is the research magazine of the european communities. First of all, Finland has chosen an appropriate burial site. It is a crystalline rock formation in the Baltic Shield. The reason they've chosen this area is because the rocks there are stable and the entire area is free of earthquakes so, geologically speaking, it's a very quiet area. Then they will just bury the canisters 500 m below surface and leave them there. It's a completely passive method: you do nothing, you just allow nature and time to take their course and allow the material to decay until it's no longer radioactive. In Finland they have estimated that it will take their waste about 250.000 years to become completely safe but they don't plan to worry for that long. In fact they will monitor the radioactivity level from the earth's surface for 350 years and then they will simply forget about it.

In fact, deep geologic burial is not even our idea, nature has been doing it for billions of years. For example, 2 billion years ago in what is now Gabon in West Africa there was a natural uranium deposit, which produced a series of nuclear reactions that lasted for a period of 500.000 years before dying away. These reactions produced a large amount of radioactive waste. Today, there is no radioactivity in the area, because the material decayed, and the entire deposit has migrated by less than 10 m, because the area was geologically quiet. This is what we are aiming for as well.

Just to sum it up, I would like to emphasise on three points:

  1. Nuclear power plants take care of their waste.
  2. The cost is internalised, so when you pay for electricity generated from a nuclear power plant you also pay for waste management and burial.
  3. There is no technology that can produce electricity on an industrial scale without polluting. There is no dilemma between "no pollution" and "pollution". The only question is what kind of pollution do we prefer. And I think we should go for the kind of pollution we can actually understand, predict and manage.