Posts Tagged ‘Nuclear decommissioning’

Road to Nowhere

September 21, 2015
A road to nowhere. This road is 60 metres below the surface of the Finnish peninsula on Olkiluotu and leads to giant silo - the end of the road for low-level and intermediate-level radioactive waste in Finland.

A road to nowhere. This road is 60 metres below the surface of the Finnish island of Olkiluotu and leads to two giant silos – the end of the road for low-level and intermediate-level radioactive waste in Finland.

I wrote last week that one of the things we in the UK need to build in ‘someone’s back yard’ is a Nuclear Waste Repository.

Last week during a progress meeting for the European Metrodecom project, I joined a visit to the site of such a repository in Finland, on the island of Olkiluoto.

Olkiluoto Island houses two working nuclear reactors, each generating approximately 400 MW of electricity for more than 95% of the time. It is also home to the first construction of a new type of reactor which may (or may not) be built at Hinkley Point in the UK. When completed this third reactor should generate approximately 1600 MW of electricity.

But more important than nuclear generation, Olkiluoto is home to Onkalo (meaning ‘Cave’ or ‘Cavern’) the world’s first final disposal site for high-level waste.

The lower levels of Onkalo are still under construction and so sadly we were not able to visit the tunnels 400 m below the surface. But we did visit the 60 m deep repositories for low-level and intermediate-level radioactive waste .

Importantly, these are not ‘storage’ facilities, but represent sites for the final disposal of this waste. When they are full, they will be sealed off and left.

The visit

After three briefings on Olkiluoto in general and Onkalo  in particular, we boarded a bus for a tour of the site, ending up at the entrance to the so-called VLJ repository.

We were asked not to take pictures of the site, but once inside the repository we were told that we could ‘fill up our memory cards’.

We put on obligatory hard hats, and after a large roller-door was raised, we descended on a sloping roadway mined from solid granite.

The tunnel descends, carved out of solid granite.

The tunnel descends, carved out of solid granite.

After 15 minutes or so we reached a large chamber containing two gigantic silos, each about 20 metres in diameter and about 40 metres deep.

Panoramic picture of the Low-level (on the left) and intermediate level (on the right) wast repository.

Panoramic picture of the low-level (on the right) and intermediate level (on the left) waste repository. (Picture from Simon Jerome). Click for larger version.

Above ground, waste is packed into concrete crates about 2 m x 2 m which are then driven along the ‘road to nowhere’ aka the repository. And then lowered by crane into the silo where they are carefully stacked.

Waste is packed into these concrete containers and lowered into the silo

Waste is packed into these concrete containers and lowered into the silo

We weren't allowed to peek into the silos, so this my photograph of a stock photograph of the silo showing the stacks of waste.

We weren’t allowed to peek into the silos, so this my photograph of a stock photograph of the silo showing the stacks of waste.

Most of this waste is ‘operating waste’ from the two existing nuclear reactors on site: typically single-use garments used by maintenance workers and operators, and ion-exchange resin used in maintaining water purity.

The current plan calls for three similar silos to be built to accommodate the decommissioned remains of the two existing reactors at the end of their lives.

Onkalo

By the time that Olkiluoto 1 and 2 reactors are being decommissioned, the Onkalo deep repository will be ready to take all the high-level waste that the reactors have produced over their lifetime.

The fuel rods from the reactors will be removed and placed in water storage for about 10 years – a backlog of fuel awaits the availability of the repository. Bundles of fuel rods are then placed inside a strong cast-iron frame and sealed inside a 4 metre long copper cylinder.

Fuel rod bundles (one visible) are placed in a cast Iron frame (right) chosen for its strength. This is then plced inside a copper cylinder chosen for its corrosion properties.

Fuel rod bundles (one visible) are placed in a cast iron frame (right) which is then placed inside a copper cylinder. Cast iron is chosen for its strength and copper is chosen for its corrosion properties.

Significantly, no attempt is made to reprocess to the fuel. This is somewhat wasteful since useful nuclear material remains unburnt in the fuel rods. But this choice dramatically simplifies the disposal.

Simulated gallery in Onkalo. The tops of several cylinders are visible. When the gallery is full, the space will be back-filled with clay and sealed with a concrete plug.

Simulated gallery in Onkalo. The top of one cylinder is visible and locations of its neighbours can be seen in the distance. When the gallery is full, it will be back-filled with clay and sealed with a concrete plug.

Comparison with the UK

The contrast between the rational Finnish approach and the UK’s ‘let’s put this off and make it someone else’s problem’ approach could not be greater.

Admittedly, Finland’s ‘back yard’ is bigger than the UK’s: they have one tenth our population and twice our land area. And additionally they require a much smaller repository than the UK will require.

However, Finland has begun preparing for disposal of waste before their first generation of reactors have reached the end of their life.

In contrast the UK has been generating about 20% of our electricity from nuclear power for around 50 years, so we have benefited profoundly from nuclear power. Our first generation reactors are now being decommissioned and we have lots of spent fuel and other types of radioactive waste.

But despite spending hundreds of millions of pounds planning, in practical terms, we have done absolutely nothing about safely disposing of nuclear waste – including high level waste.

Some is stored in warehouses, but shamefully a great deal is stored in filthy outdoor pools.

Outdoor storage of nuclear waste at Sellafield

Outdoor storage of nuclear waste at Sellafield.

My visit filled me with a sense of national shame. But overall I feel pleased to have seen this site with my own eyes. Finland has shown the world that safe disposal of nuclear waste is possible, and not at an extravagant cost.

And if they can do it, then why can’t we?

 

Ready for final disposal

Ready for final disposal

What do you do with an old nuclear reactor?

September 11, 2014
To search for tiny additional additional amounts of radiation you first need to screen out the normal level of radioactive background.

To search for additional amounts of radiation in the scrap from a nuclear power station you first need to screen out the normal level of radioactive background. To do this you must build a ‘chamber’ using special, non-radioactive bricks.

I find myself in the Hotel Opera, Prague this rainy Thursday evening, tired after having spent a fascinating day at the Czech Centre for Nuclear Research UJV Rez.

There I saw one outcome of a European collaboration (called MetroRWM) designed to answer just one of the difficult questions that arises when one needs to take apart an old nuclear power station. This is something Europe will need to become good at in the near future.

This didn’t concern the highly-radioactive parts of the power station: that’s another story.

This concerned the 99% of a nuclear power station which is no more radioactive than a normal power station.

What should happen is that this material should join the normal scrap system and be re-used.

However, the understandable surplus of precaution that surrounds nuclear matters will prevent this, unless every single bucket load of concrete or scrap metal can be verified to have a level of activity less than a specified standard.

The collaboration based at UJV Rez have built an apparatus to do just that. And most importantly, they have proved that it works i.e. that tiny hot-spots on the inside of pipes can be detected quickly and reliably.

Here is how it works.

To detect the tiny levels of radiation potentially coming from hidden radioactive particles, the apparatus uses ultra-sensitive radiation detectors.

However these detectors are useless if they are not shielded because our normal environment contains too much radioactive material. So the first step is to shield the detectors.

The low radiation chamber at UJV Rez At teh far end you can see a fork lift truck loading a pallet which will travel through teh chamber and emerge at this end.

The low-background chamber at UJV Rez At the far end you can see a fork lift truck has just loaded a pallet which will travel through the chamber and emerge at this end. The doors at this end are currently closed.

The UJV team did this by building a ‘room’ using a special type of brick which is almost as good as lead at keeping out radiation, but much cheaper, much lighter, and much easier to work with. Using this they lowered the level of radiation inside to just 1% of the background radiation.

The sensitive radiation detectors can be seen inside the room as the doors open to allow the entry of test pallet.

The two ultra-sensitive radiation detectors can be seen inside the shielded room as the doors open to allow the entry of test pallet.

They then built a system for loading pallets of material on a conveyor at one end, and drawing it through the shielded room to check the radioactivity in all parts of the pallet. The measurement took about 5 minutes, and after this the pallet emerged from the other end (Video below).

The key questions are:

  • How do you ensure that ‘not detecting something’ means that there is none there?
  • Could some activity slip through if it were shielded by some gravel, or steel piping?
  • Could it slip through if it was in the bottom corner of the pallet?

To answer these questions the UJV team, in collaboration with scientists across Europe, created samples that simulated many of these possible scenarios.

Pallets of 'radioactive' waste

Pallets of ‘radioactive’ waste. These pallets are a standard size, but there thickness is determined by the need to be sure any radioactivity trapped inside can be detected. The pallets above have been made very slightly more radioactive than the background.

One of their clever ways of testing the machine was to create samples of known radioactivity and place them inside hollow steel balls (actually petanque balls!).

A colleague showing a very low level sample of known activity coudl be place inside a hollow steel ball,simulating radiation trapped inside steel pipes.

A colleague showing a very low level sample of known activity which can be placed inside a hollow steel ball,simulating radiation trapped inside steel pipes.

The machine could then search for the activity when the balls were arranged in many different ways.

A pallet filled with steel balls, some of which have radioactive samples of known activty concealed inside.

A pallet filled with steel balls, some of which have radioactive samples of known activity concealed inside.

The aim of all this effort is that at the end of the day, scrap material like that in the picture below can be rapidly screened on-site and sent to be recycled in the confidence that no hazard will ensue at any time in the future no matter how this material is treated.

The aim of the system is to screen very diverse scrap such these old pipes and ducts.

The aim of the system is to screen very diverse scrap such these old pipes and ducts.

These measurements are not easy – but this work really impressed me.


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