Sunday, 9 January 2011

It's not waste it's used fuel!



We all know that nuclear power often suffers with a public perception problem. The industry has done itself few favors over the years by permitting and even acknowledging certain to be regarded materials as waste.  The main material I want to focus on for the next few blog entries is uranium fuel.

Values used in my writing will relate to typical numbers for PWR type reactors but the principles apply to any thermal neutron reactor that uses Uranium fuel.

Natural uranium is mined and processed, enriched and fabricated into fuel. Reactor fuel is typically enriched to around 3.6% to 4.1%. That means the U-235 (which is needed for is fissile properties) is increased to that percentage over the more abundant U-238. In contrast natural uranium as mined contains  around 0.7% U-235.

The diagram to the right illustrates the concept of enrichment. I have left the weapons grade enrichment of uranium in place to illustrate just how much enrichment is required to obtain something that could be used in a nuclear weapon verses what is used in reactors. It is important to realise that low enriched Uranium (LEU/Reactor grade) is VERY different to high enriched uranium (HEU/Weapons Grade).

So this reactor grade uranium in the form of fuel assemblies goes into a power reactor. In current reactors it will generally remain there for at least 18 months where the reactor will use it to generate electricity. The fuel assemblies are eventually removed and replaced with new fuel. However what is not obvious is the "spent" fuel that is removed has had less than 1% of the available energy it contains used.



This "spent" fuel, which from now on I will call used fuel is as it is in no way spent is currently generally labeled as waste and treated as such.

The majority of the fuel will still be uranium except it will now have other radioactive elements present known as fission products and actinides. We want to recover most of what is found in the used fuel as it can be used for other purposes mainly producing more fuel.

Currently used fuel will be stored for a number of years often on site at the reactor as it will continue to produce radioactive decay heat. This cooling usually happens in fuel pools which are as exactly what they sound like, pools of water.

Currently the intended destination for this used fuel following several years of cooling is geological storage underground. However to date no undeground geological repository has been brought into operation.

Why are we looking to store used fuel that has 99% of it's energy remaining underground? In the past nobody was quite sure if this used fuel was an asset or a liability. This has led to the used fuel being poorly branded as waste along with all the perception problems that generates.

People rightly ask, "if this isn't waste why must we lock it underground?". Right now we need to shake of the idea that used fuel is waste. Lets not even brand it "spent fuel". Spent implies that it's of no further use and that is energy is depleted.

This is not the case. What comes out from a nuclear reactor is not and should not be viewed as waste. With a combination of reprocessing and recycling this used fuel can be used again and again to provide ultra-low/carbon free power for at least several thousand years.

So the next time somebody asks "Well what about the waste?" at least explain that the fuel isn't really waste at all and can be reused if we want to and we are not simply leaving burdensome 'waste' behind for the next generation. 

More to come on the how of recycling next time.

4 comments:

  1. I can't believe used fuel still has it's benefits. The idea of recycling fuel is very wise, not only in saving cost but also in saving the environment from further destruction.
    fuel trailers

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