The science of nuclear energy
The science of nuclear energy

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

The science of nuclear energy

2.3.7 Solution: deep geological repository

The favoured option for nuclear waste management around the world at the time of writing, 2015, is to bury the waste in purpose-built underground repositories.

The siting of such a repository requires much thought as many of the fission products will remain active for thousands of years. Thus, a repository needs to be secure, both now and into the far flung future!

There are two main issues that need to be considered:

  1. The possibility of seismic activity. Earthquakes could bring the material to the surface.
  2. The problem of water. It is vital that water is not able to come in contact with the radioactive material now or in the future.

In order to reduce the possibility of either of these problems arising, the design of repositories includes containers with multiple layers enclosing the waste and other engineered barriers or seals around the containers. Great attention is also paid to the suitability of the surrounding environment, particularly the geology in terms of stability and rock composition, and the way water can move through it. Several processes combine to cycle water globally, and these in Figure 20.

Described image
Figure 20 The global water cycle: showing the distribution of the world’s water. ‘Lakes’ includes freshwater and saline lakes. The values shown as transfers represent the amounts of water cycled annually (in units of 1015kg y-1), as opposed to that stored in reservoirs (in units of 1015 kg)

At any stage in the water cycle where evaporation occurs, anything dissolved in the water is left behind. In particular, radioisotopes transported into the oceans would accumulate there; they would not evaporate and re-enter the water cycle.

How water flows through the ground is largely determined by the geology. Many of the rocks that make up the Earth’s crust contain voids, which can hold water. These voids can take various forms. In sandstones, for example, they consist of small interconnected pores between the grains of sand. In granites, which are made up of interlocking crystals, there may be fissures or fractures, which can be interconnected so allowing water to travel through the rock. Below a certain level, the rock voids are all filled with water. This level is called the water table, and the rocks below it are said to be saturated. By using the voids as a pathway, water can flow through the saturated rocks.

Described image
Figure 21 Void structures in different rock types.

The ease with which water flows through rocks varies with the rock types. For example, if the rock contains large well-connected pores or voids, like the sandstone in (a), or extensive linked fractures, like the granite in (b), the water will flow easily through the rock. In (c) there are large pores in the rock, but the pores are not interconnected, so the water cannot flow easily through the rock. Any repository would ideally need to sit above the water table and within a rock that resisted the flow of water.

In the next section you’ll see a video of the planning for a depositary in Yucca Mountain, a mountain in Nevada, US. This site was deemed to be near perfect as regards its geology.

OUFL_18

Take your learning further371

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses372.

If you are new to university level study, we offer two introductory routes to our qualifications. Find out Where to take your learning next?373 You could either choose to start with an Access courses374or an open box module, which allows you to count your previous learning towards an Open University qualification.

Not ready for University study then browse over 1000 free courses on OpenLearn375 and sign up to our newsletter376 to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371