Nuclear waste – Can it be disposed of safely?

If you’re reading this, and you oppose nuclear energy, there’s a good chance that you do so as you’re concerned about nuclear waste. In fact, if you’re reading this and support nuclear energy, there’s a good chance you’re still somewhat concerned about nuclear waste. This concern is very reasonable – there’s a lot of fear in the public mind about nuclear waste, and not a lot of easy to access information about what it is, and what can be done with it. In fact, I myself was once opposed to nuclear energy, and when I did, a main reason was nuclear waste.

 

What is nuclear waste?

In the production of power from nuclear reactor, there are several different kinds of waste produced – Low Level Wastes (LLW), Intermediate Level Wastes (ILW) and High Level Wastes (HLW).  The LLW and ILW include everything from lightly contaminated equipment and fluids used within a power station, up to the dismantled reactor cores and other components. However, what people usually think of when they hear the term nuclear waste is the spent fuel – the uranium rods that have been ‘burned’ in a nuclear reactor, and the plant operator no longer wants to use.

Nuclear and Renewables – How they can work together

The opposition to the continuing existence of a largely fossil-fuel based economy can be loosely divided into two key groups: The first propagate that a reliance on coal, oil and gas should be replaced with the exploitation of renewable energy sources, such as wind, solar and biomass; The second group support the growth of atomic energy, and envision a future society where hydrocarbon power plants are replaced by nuclear alternatives. It is frequently asserted, by members of both groups, that the two approaches are incompatible with each other – that we are faced with an either-or decision. We can either take the ‘nuclear option’, or go for an entirely renewable energy future. I personally believe that both positions are false. The evidence that I have seen leads me to the conclusion that nuclear and renewables can not only work well together, but an energy solution including elements of both would be more economical and have a higher chance of success than relying on one source of energy alone.

Let’s start by looking at some of the advantages and disadvantages of nuclear and renewable energy.

Into Eternity: Fact or Fiction?

I watched ‘Into Eternity‘ last night on More4 (It was titled ‘Nuclear Eternity’ on the channel here), and I must say the film was a wonderful work of art. The imagery was fantastic, the music was entertaining, the narrative compelling. However, being an engineer I was somewhat frustrated by the lack of technical discussion, and instead a heavy reliance on philosophical questions. If you’ve seen the film, and I suggest you do before reading this entry, you’ll notice that the interviewees (mostly technical staff working on the Onkalo repository) were somewhat taken-a-back by this kind of question.

So, in this entry, I’d like to discuss some of the technical issues which I believe were somewhat missed in the film. The first is the issue of how long the waste has to be stored for. The 100,000 years needed to store spent fuel is based on the radiological toxicity (how dangerous it is to humans).

As can be seen from the diagram, the danger from the fission products (what you get when you split the uranium atom) is more or less gone after between 500-1000 years. These are the worst bit of the waste, and they are what you want to guard against. After this, you have the actinides remaining. In a nutshell, these are what you get when uranium captures a neutron, but doesn’t split. These are still dangerous if you ate or came into contact with a large amount of them, but they will be largely diluted by the rest of the material in the repository. They also happen to be some of the heaviest elements known to man, and so are unlikely to ever migrate to the surface, even if they come into contact with water. As can be seen from the diagram, they are the reason why the spent fuel is still more radiotoxic than the original ore for a period greater than 1000 years.

Could a ‘Fukushima’ happen in the UK?

(This blog should be read following the previous post ‘Could a Chernobyl happen in the UK?’).

Due to the events recently concerning the situation in Japan, I’ve decided to supplement my previous blog ‘Could a ‘Chernobyl’ happen in the UK?’ with some further information.

The first thing that I’d like to point out is that a 41 year old reactor has been hit by one of the worlds most intense earthquakes, coupled with a huge tsunami, and yet remains largely intact (the primary containment remains isolated) and significant melting of the fuel has been avoided. A dangerous amount of radiation has not been released, and there have been no fatalities amongst the public.

Rather than a boost to the ‘told you so’ attitude of the nuclear opponents, these latest events are surely a sign of the robust safety of nuclear power. In contrast, hundreds have been killed or injured in fossil fuel plants around the country.

It’s also worth noting that the UK is not near any major fault-lines,  so our nuclear generating infrastructure is not subject to the same risks.

However, just to set worried minds at ease, I’ve decided to highlight some of the safety features of a modern nuclear power plant design (such as the AP1000 and the EPR, as was looked at in detail on the previous article). These features would prevent even the very minor consequences experienced at Fukushima.

The first is the advanced and substantial containment and shield buildings present in both designs. As we noted previously the EPR has a doubled layer containment dome, and the ap1000 has a separate shield building.

As you may have heard, the Fukushima back-up diesel  pump systems failed, possibly due to sea-water contamination (or they may have just been old and unreliable). In the EPR design there are four separate diesel systems, each capable of providing cooling to the core. Two of these four systems are ‘bunkered’ and so are protected from external hazards. The safety back up systems of the AP1000 are based on a  ‘passive’ arrangement, and are located within the primary containment (so would not be subject to external hazards). Passive systems are designed to operate in a ‘fail safe’ system, where simplicity is favoured over complexity (far less chance of age-related failure).

You’ve no doubt seen the explosions on TV. This was caused by hydrogen formation and venting to the atmosphere. In both the AP1000 and the EPR systems are present that safely recombine or ‘burn’ the hydrogen in an accident scenario and so avoid the possibility of an explosion of this type.

You’ve also no doubt have heard about the effort to cool the Fukushima cores with sea water. In an extreme accident scenario, the pumping of seawater would not be necessary in one of the two modern designs noted here. A large vat of water sits on top of the reactor core of the EPR and Ap1000, and could simply be drained in directly.

Finally the operators inside the plant are safe from any possible increase in radiation due to the a ‘control room  habitability’ system, which vents the work space and provides safe levels of air. If this is not enough, both the AP1000 and EPR can be controlled remotely – i.e operators would not need to be on site to control the reactor.

Could a ‘Chernobyl’ happen in the UK?

A large proportion of the discussion on nuclear power is centered around the possibility of a ‘severe accident’ at a power station. More specifically, the infamous accident at Chernobyl reactor No.4 is the first thing that comes to mind when the topic is raised.

Opponents of nuclear power often highlight claims made about the projected casualties of the accident. Some proponents of nuclear power suggest that other than the immediate casualties of the blast and the clean-up there is little evidence of any further deaths caused by the accident. The claims range from 56 to 945,000 fatalities as a result of the subsequent release (The World Health Organization estimates 9,000 worldwide early deaths will occur as a result of elevated radiation levels across Europe).

In this article, I wish to discuss the likelihood (If any) of an accident similar in consequence to Chernobyl happening in a modern reactor, of a design most likely to be built here in the UK over the next 10 years.

Draft Charter

The first step in building this organisation is perhaps to decide what its goals are. In doing this, the development of a charter seems a wise idea. This will of course be subject to revision and further additions etc.

These are some preliminary ideas that I have had. Perhaps they should later be divided into goals/objectives etc:

• Promote, through an evidence based approach, the use of Nuclear Energy for Electricity Generation and other applications.