Nuclear has had a bad year. Fukushima is a tragic reminder that even modern technology is fallible, and when things go wrong in the nuclear sector, they go very badly wrong. The jury is still out on the long term impact of the Janapese incident, but nevertheless public support for nuclear power around the world is as cautious as ever.
However, with an urgent need to produce vast quantities of clean and secure energy, the UK amongst many other nations is about to embark on a ‘nuclear renaissance’ with a planned investment of £300 billion in the nuclear sector over the next two decades.
What is to be done about the nuclear waste generated? A technological challenge like no other, it will be 100,000 years before its radioactivity drops to safe levels and, as such, it will need to be stored safely as civilisations rise and fall around it. The answer may lie in deep underground geological disposal, yet this strategy faces strong ‘Not In My Back Yard’ opposition.
Since Enrico Fermi first achieved criticality in an unshielded pile of uranium and graphite bricks on an abandoned racket court at Chicago University, the nuclear effort has never been incident free. However, despite the catastrophic scale of the largest nuclear incidents, the vast majority of nuclear plants live out their lives quietly and reliably. Based on the International Atomic Energy Authorities (IAEA) ‘incident record’, there have been a total of 33 significant incidents in nuclear history, all of which have been classified as less serious than Chernobyl.
A technological challenge like no other, it will be 100,000 years before its radioactivity drops to safe levels and, as such, it will need to be stored safely as civilisations rise and fall around it
Despite safety concerns and the potential for catastrophic accidents, nuclear is still regarded as an excellent proposition as a secure supply of cost competitive and green energy. This portfolio of qualities has not been overlooked by policy-makers. The world’s 435 operational reactors1 now account for over 15% of global electricity supply,2 and in the UK our 10 operational nuclear plants power over 16% of all our electricity. The UK anticipates investing £300 billion in the nuclear sector over the next two decades4 in the race to reduce emissions from the pow er sector to 80% of 1990 levels by 20505. In China this nuclear future is already well underway with 26 plants under construction6 – the biggest deployment program in nuclear history.
Furthermore, Uranium fuel is readily available, cheap to extract, and known reserves total over 5 billion tonnes – enough to sustain current consumption for 80 years3. Better yet, the majority of these reserves are found in politically stable countries – Australian ore reads much better than Russian gas from an energy security perspective today.
And the waste? Barely a barrel. The nuclear process is so energy rich that a typical 1GW reactor will discharge only 27 tonnes of spent fuel in a full year of operation. At this capacity, a coal-fired plant will release 125,000 tonnes of (significantly radioactive) fly ash7 and more than 40 times as much CO23. In the UK one palm sized ‘puck’ of waste is all that’s required to supply each citizen with a lifetime’s electricity. Indeed the energy to waste ratio is so high that a recent government inventory8 puts all the highly active waste from 50 years of British nuclear power at a mere 12,600m – not even enough to fill the stalls of the Royal Albert Hall.
The Fuel Cycle
Releasing nuclear energy is deceptively straightforward. Upon arrival at a power station prefabricated fuel rods need only be loaded into the reactor where, immersed in a sea of neutrons, they spontaneously liberate their nuclear energy, heating water and generating electricity in the conventional way. During this time the fissile uranium isotope U235 is ‘burnt’ and the daughter nuclei build up as ‘ashes’ within the rods. These non-reactive species absorb neutrons and so their rising concentration ‘poisons’ the reactor and the old rods must be removed.
The rods are now extremely radioactive – crammed with unnatural isotopes which must decay to stable forms via the release of dangerously high energy particles. These nuclear processes keep the spent fuel rods as hot as 300°C long after they are removed from the reactor. They must be lowered into water tanks to be cooled, where they will be stored for several years before they can be safely packaged for transport.
Today around 90% of the world’s waste3 remains in such cooling tanks or is packaged and moved to warehouses for temporary, but indefinite, storage in the shadow of the reactor that produced it. In the UK, cooled waste is sent by rail to the nuclear reprocessing site of Sellafield, Cumbria. Here the 97% un-burnt fuel is chemically isolated from the 3% highly radioactive ashes. The latter are then encapsulated in glass cylinders and sealed in steel barrels. This waste is then provisionally stored on site whilst new fuel rods are manufactured from the recycled Uranium.
A Solution for Eternity
Despite an extraordinary cool-off period, it isn’t the radioactivity that presents the biggest obstacle to safe disposal. A few feet of steel and concrete are more than sufficient to ensure exposure-free handling and transportation of these wastes, sometimes half way around the world. It is when these carefully engineered canisters become damaged and allow radioactive materials to escape into the environment that the problems begin. Most hazardous of all is contact with water – suddenly the soluble radioactive elements have unhindered opportunity to move lethal doses directly into the food chain.
Try as we may to guard against every eventuality, such leaks, although uncommon, are inevitable. Even under draconian regulation, Sellafield’s THORP reprocessing plant suffered a major internal rupture in 2005, leaking 20 tonnes of reprocessed fuel into its secondary containment vessel. Elsewhere the situation is often significantly worse – the dilapidated Russian naval waste facility at Andreeva Bay has been so heavily contaminated by rusted barrels and cracked storage ponds that it is now isolated under international stewardship for a decommissioning operation that will cost millions9.
How can we prevent such leakage now, and in the foreseeable and unforeseeable future? Nuclear scientists must overcome the critical challenge of preventing nuclear waste exposure or leakage for the 100,000 years required for its radioactivity to decay to safe levels.
Digging Deep
Since the dawn of nuclear power the waste problem has been tackled with the same perspective – if isolated appropriately, it will be possible to store the waste safely and securely. In 1956 it was the US National Academy of Sciences that first urged the final disposal of high-level nuclear waste in purpose-built underground storage facilities. Trapped outside the biosphere for well in excess of 100,000 years – barely the blink of an eye in geological time – it will remain at a safe distance from human life long after its containers have rusted away.
Around 90% of the world’s waste [is] moved to warehouses for temporary, but indefinite, storage in the shadow of the reactor that produced it
Since then researchers have been streamlining designs for such underground repositories. Success of these facilities depends critically on location. The repository chamber must be at sufficient depth to be fully insulated from surface processes. Surrounding rock must be impermeable to ground water flow – minimising corrosion and guarding against water borne dispersal from fractured canisters. Yet it must be porous enough to enable safe dispersal of potentially explosive outgasing of decaying fuel. Last, but not least, the site must be tectonically stable and natural resource free, ensuring neither natural nor industrial intrusion disturbs the waste in its final resting place. A multi-barrier strategy has been devised: ‘engineered barriers’ are buried within appropriate host rock (‘geological barriers’) such that man-made and natural boundaries together ensure the waste is permanently isolated.
The world’s first such facility – the Waste Isolation Pilot Plant (WIPP) – accepted its inaugural shipment in March 1999 in Carlsbad, New Mexico. Here, after a planned 30 years of shipments11, the rock salt bedrock will ultimately ‘flow’ into all of the repository’s cracks and crevasses, sealing the nuclear legacy of US defence 650m beneath the desert. The project will cost an estimated $2 billion12 over its lifespan.
Carlsbad repository’s sister project for civil waste at Yucca mountain, Nevada, tells a very different story. With no nuclear power plants in the state, and the population already victim of Nevada Test Facility fallout, a two-thirds majority of Nevadans consistently opposed the project which was eventually shelved in 2011 after 30 years and $9 billion of research and consultation.
Lessons have been learnt. The Posiva facility, under construction on the Finnish island of Olkiluoto, is the world’s most advanced repository and currently running to time and on budget. Due to accept its first shipments in 2020, used fuel loaded directly into cast iron holders will be sealed in 5cm thick corrosion resistant copper canisters which will then be stacked inside impermeable cavities in the repository. The lifetime cost of the facility is estimated at £2.5 billion.
It will require decades of consistent policy to ensure that our nuclear waste does not pose a potentially catastrophic risk to generations far into the future
In the UK, it is planned that a similar disposal site will be constructed from 2025. Lumbered with 50 years of civil nuclear waste, plans for a prototype repository were put forward in the early nineties, however discussions on its location are ongoing.
Trialled successfully for Posiva, site selection is to proceed on a ‘volunteerism’ principle by which interested communities may bid to host the facility and its decades worth of investment. Two districts in Cumbria are still in the running – the basis for public support being that most UK radioactive waste is already closeby at Sellafield anyway. The British Geological Survey deems 75% of Cumbrian land sufficiently far from iron and coal reserves that might tempt future generations to start digging, however concerns persist about gas leakage.
As of March 2012 a public consultation is underway to determine if Cumbrians are committed to the next step. Ministers, when asked if there was a Plan B, in case the consultation failed, have repeatedly said that Plan B is to make Plan A work – there is no alternative site.14
Final Disposal?
With the next generation of nuclear plants expected to produce over 20% of UK electricity by 20305, cohesive plans for long-term nuclear waste storage are more crucial than ever. Furthermore, questions persist at the scientific level: can we efficiently mutate the waste into stable elements? Faced with a 100,000 year legacy, such avenues for fresh research seed political uncertainty – should we ensure repository waste is recoverable in case future generations can or wish to tackle it more effectively?
One thing is for certain – decisions need to be made. It will require decades of consistent policy to ensure that our nuclear waste does not pose a potentially catastrophic risk to generations far into the future. Until then, where is our nuclear waste going? Nowhere further than a warehouse at Sellafield.
