Nuclear Power – Dealing with waste and carbon emissions

Last article looked at how a nuclear power plant produces electricity. However, one problem with nuclear power stations is the production of nuclear waste, a highly toxic, highly radioactive substance made up of the spent fuel rods. Part 2 looks at dealing with nuclear waste, and looks at just how carbon friendly nuclear power really is.

 

Nuclear waste

After removal from a nuclear reactor, the spent fuel rods are stored in deep pools of water for several years to literally cool off and allow some decay of the radioactivity. These waste fuel rods are then removed, and there are two possibilities. They can either be transported and stored as is, or processed to remove any useful remnants. While processing occurs in Europe and Japan, at the moment there is no waste processing in the US.

 

A spent fuel rod will normally contain somewhere in the region of 0.8% Uranium-235, which, along with the Uranium-238 in the rod, can be extracted and reused to make new fuel rods. The waste also contains radioactive materials which are useful in medicine which can also be extracted and used. However, reprocessing fuel rods does allow the extraction and concentration of Uranium-235 and plutonium, another particularly reactive atom, which could be then used for weapons. The reprocessing of spent nuclear fuel is extremely technical and requires highly specialised equipment, including itself a particular type of nuclear reactor. As a result very little reprocessing is done with France, one of the highest fuel re-processors, only recycling around 28% of its yearly fuel. Due to this special type of nuclear reactor and other specialised equipment and processes the extraction and reuse of Uranium for nuclear fuel is very expensive, and is only viable when the prices of uranium are high.

 

On average, a nuclear power station produces between 20 and 200 tons of waste per year. Due to its toxicity and radioactivity, it needs to be stored in a location which effectively removes it from the environment. At present however, most waste is believed to be stored at the individual power stations, although there have been suggestions for centralised repositories. A centralised facility would bring all the radioactive waste into one ideal location separated from population centres. The United States conducted feasibility studies on storing waste underground in the Yucca Mountains however abandoned the idea. Australia has also considered locations for nuclear waste storage in the deep outback

 

Nuclear waste in storage

A central storage site would normally be in a remote area far from water sources to provide protection to the population in case of a leak of radioactive material. The Australian outback option is also in an area of geological stability, meaning there is not likely to be any major earthquakes which may affect the containment of the waste, and underground storage provides shielding at ground level from radiation. Such a facility would likely involve the digging of a large pit which is then lined with concrete to act as containment for any leaks. Waste canisters would be placed in the pit, and the pit filled in. A location such as the Australian Outback would limit the exposure of the canisters to moisture such as rain, and as a result corrosion of the containers would be minimal. However, should there be any leaks, the waste would theoretically be contained within the concrete-lined pit.

 

The Swedish system for disposal of nuclear waste uses caves 500 metres underground. Firstly, the radioactive waste is stored at the nuclear station for up to 30 years, after which it is placed in an iron capsule. This iron capsule is then encapsulated using copper. An 8 metre deep hole is drilled in the cave, into which the copper capsule is placed, and the hole then filled with bentonite clay which will soak up any leaks. The combination of copper, which will not corrode, and clay should prevent any toxic waste from escaping into the environment. When the storage cave is full the entrance is permanently sealed.

 

A Swedish copper canister for storing nuclear waste

When stored properly, radioactive waste is not something to be as fearful of as some people would have you believe. It may surprise you to know that at any given time, there is radioactive waste stored in most universities and major hospitals worldwide, waiting transport to a long-term storage facility. As long as the means of storage are secure, it actually poses little risk to the surroundings.

 

Nuclear waste does have a long life-span however. It takes at least 1000 years for the Uranium-235 in radioactive nuclear waste to reach the radioactivity levels of natural uranium, and sometimes up to 10,000 years for it to reach levels which are no longer toxic. However, only about 3% of Uranium-235 will be radioactive for that long time, with most waste no longer being hazardous from radioactivity after tens of years. However, there are other radioactive components in nuclear waste which remain radioactive for much longer periods. In fact it has been recommended that storage for up to 1 million years may be required before it can be considered completely safe. This problem is not only confined to the nuclear industry however, other industrial waste from non-nuclear industries includes heavy metals such as cadmium or mercury, which remain hazardous indefinitely. Radioactive waste only forms around 1% of toxic waste in countries with nuclear power.

 

The mining of uranium also produces large quantities of toxic waste. The extraction of uranium from the mined ore requires toxic chemicals such as sulphuric acid and hydrogen peroxide, for example. Additionally, the waste products from the extraction process include large quantities of radioactive water. Currently these are stored at the mine site in large dams; however spills from the dams are known to have occurred at Ranger in the Kakadu National Park.

 

Due to its extremely long life span, there are questions however about how securely the waste products from uranium mining and fuel use will be stored in the future. In particular, breakdown of the container holding the waste may allow the waste to seep out, polluting the nearby area. Sweden stores its waste in copper canisters believing the stable nature of copper will prevent any breakdown and release of waste.

 

Carbon friendly?

One of the major reasons given for a change to nuclear power stations is to reduce carbon dioxide emissions into the atmosphere. In the battle to reduce the effects of human-induced climate change, any technologies which reduce CO2 output are seen as valuable.

 

A recent study which combined the results from over 100 earlier studies examined the greenhouse gas emissions of several energy production technologies over their lifecycle. The results are shown in the table below.

 

Technology

Carbon emissions (grams CO2 per kilowatt hour)

Onshore wind farm

10

Hydroelectric reservoir

10

Solar photovoltaic panel

32

Geothermal “hot rocks”

38

Nuclear

66

Natural gas

443

Coal

960-1050

 

Nuclear produces around 66 grams of CO2 for every kilowatt hour of energy produced, compared to around 1000 grams of CO2 for coal fired plants, over their entire lifecycle. Geothermal power, which uses hot rocks deep below the Earth’s surface to heat water and produce steam to turn generators, emits around 38 grams of CO2 for every kilowatt hour of energy, while wind turbines emit around 10 grams of CO2 for every kilowatt hour. These figures take into account the mining of coal or uranium, construction of each of the power stations, any waste disposal and decommissioning of the station at the end of its lifetime.

 

From these results it is obvious that even with the carbon emissions associated with mining of uranium, building the power station and disposing of the waste, nuclear power still emits far less greenhouse gases than coal or natural gas powered stations, the major forms of power generation in Australia. Renewable resource-powered stations such as wind, hydroelectric or geothermal still do emit less greenhouse gases however. So while there would be a considerable effect on carbon emissions by replacing coal or natural gas fired power stations with nuclear, further savings could potentially be made by developing new renewable powered stations.

 

So nuclear power stations do produce less CO2 than a coal fired plant, but what about radiation levels? Possibly contrary to popular belief, nuclear power stations release effectively no radiation. In fact a nuclear power station releases less radioactive material into the atmosphere during operation than a coal power station. The ash produced from burning coal contains small amounts of uranium and thorium, another radioactive substance, which is emitted into the atmosphere and can contaminate nearby land and water. This ash results in a coal fired power station releasing at least 100 times more radiation into the environment than a nuclear plant producing the same amount of electricity. However, to put it in context, the amount of radiation a human would be exposed to in a year of living near a coal power station is around 1/180th the levels that humans are exposed to each year normally just in background radiation. In other words, there is effectively no risk from radiation by living near either a coal plant or a nuclear plant.

 

There are many economic questions over nuclear power, and new more carbon friendly power generation technologies are either currently in development or coming online. Whether it is viable to go nuclear in Australia depends on these and other factors, including the requirement for extremely large amounts of water during the mining of uranium. One new technology which may be promising as an energy source is hydrogen power; however there are some pitfalls to that too. In the near future I’ll be blogging about one of the new technologies being developed which may make hydrogen power more attractive as an option.

 

Nuclear waste

After removal from a nuclear reactor, the spent fuel rods are stored in deep pools of water for several years to literally cool off and allow some decay of the radioactivity. These waste fuel rods are then removed, and there are two possibilities. They can either be transported and stored as is, or processed to remove any useful remnants. While processing occurs in Europe and Japan, at the moment there is no waste processing in the US.

 

A spent fuel rod will normally contain somewhere in the region of 0.8% Uranium-235, which, along with the Uranium-238 in the rod, can be extracted and reused to make new fuel rods. The waste also contains radioactive materials which are useful in medicine which can also be extracted and used. However, reprocessing fuel rods does allow the extraction and concentration of Uranium-235 and plutonium, another particularly reactive atom, which could be then used for weapons. The reprocessing of spent nuclear fuel is extremely technical and requires highly specialised equipment, including itself a particular type of nuclear reactor. As a result very little reprocessing is done with France, one of the highest fuel re-processors, only recycling around 28% of its yearly fuel. Due to this special type of nuclear reactor and other specialised equipment and processes the extraction and reuse of Uranium for nuclear fuel is very expensive, and is only viable when the prices of uranium are high.

 

On average, a nuclear power station produces between 20 and 200 tons of waste per year. Due to its toxicity and radioactivity, it needs to be stored in a location which effectively removes it from the environment. At present however, most waste is believed to be stored at the individual power stations, although there have been suggestions for centralised repositories. A centralised facility would bring all the radioactive waste into one ideal location separated from population centres. The United States conducted feasibility studies on storing waste underground in the Yucca Mountains however abandoned the idea. Australia has also considered locations for nuclear waste storage in the deep outback

 

A central storage site would normally be in a remote area far from water sources to provide protection to the population in case of a leak of radioactive material. The Australian outback option is also in an area of geological stability, meaning there is not likely to be any major earthquakes which may affect the containment of the waste, and underground storage provides shielding at ground level from radiation.

 

The Swedish system for disposal of nuclear waste uses caves 500 metres underground. Firstly, the radioactive waste is stored at the nuclear station for up to 30 years, after which it is placed in an iron capsule. This iron capsule is then encapsulated using copper. An 8 metre deep hole is drilled in the cave, into which the copper capsule is placed, and the hole then filled with bentonite clay which will soak up any leaks. The combination of copper, which will not corrode, and clay should prevent any toxic waste from escaping into the environment. When the storage cave is full the entrance is permanently sealed.

 

 

 

IMAGE

A Swedish canister for storing nuclear waste

 

 

 

When stored properly, radioactive waste is not something to be as fearful of as some people would have you believe. It may surprise you to know that at any given time, there is radioactive waste stored in most universities and major hospitals worldwide, waiting transport to a long-term storage facility. As long as the means of storage are secure, it actually poses little risk to the surroundings.

 

Nuclear waste does have a long life-span however. It takes at least 1000 years for the Uranium-235 in radioactive nuclear waste to reach the radioactivity levels of natural uranium, and sometimes up to 10,000 years for it to reach levels which are no longer toxic. However, only about 3% of Uranium-235 will be radioactive for that long time, with most waste no longer being hazardous from radioactivity after tens of years. However, there are other radioactive components in nuclear waste which remain radioactive for much longer periods. In fact it has recommended that storage for up to 1 million years may be required before it can be considered completely safe. This problem is not only confined to the nuclear industry however, other industrial waste from non-nuclear industries includes heavy metals such as cadmium or mercury, which remain hazardous indefinitely. Radioactive waste only forms around 1% of toxic waste in countries with nuclear power.

 

The mining of uranium also produces large quantities of toxic waste. To extract the uranium from the mined ore, toxic chemicals such as sulphuric acid hydrogen peroxide. Additionally, the waste products from the extraction process include large quantities of radioactive water. Currently these are stored at the mine site in large dams; however spills from the dams are known to have occurred at Ranger in the Kakadu National Park.

 

Due to its extremely long life span, there are questions however about how securely the waste products from uranium mining and fuel use will be stored in the future. In particular, breakdown of the container holding the waste may allow the waste to seep out, polluting the nearby area. Sweden stores its waste in copper canisters, believing the stable nature of copper will prevent any breakdown and release of waste.

 

Carbon friendly?

One of the major reasons given for a change to nuclear power stations is to reduce carbon dioxide emissions into the atmosphere. In the battle to reduce the effects of human-induced climate change, any technologies which reduce CO2 output are seen as valuable.

 

A recent study (INSERT LINK http://www.nirs.org/climate/background/sovacool_nuclear_ghg.pdf) which combined the results from over 100 earlier studies examined the greenhouse gas emissions of several energy production technologies over their lifecycle. The results are shown in the table below.

 

Technology

Carbon emissions (grams CO2 per kilowatt hour)

Onshore wind farm

10

Hydroelectric reservoir

10

Solar photovoltaic panel

32

Geothermal “hot rocks”

38

Nuclear

66

Natural gas

443

Coal

960-1050

 

Nuclear produces around 66 grams of CO2 for every kilowatt hour of energy produced, compared to around 1000 grams of CO2 for coal fired plants, over their entire lifecycle. Geothermal power, which uses hot rocks deep below the surface to heat water and produce steam to turn generators, emits around 38 grams of CO2 for every kilowatt hour of energy, while wind turbines emit around 10 grams of CO2 for every kilowatt hour. These figures take into account the mining of coal or uranium, construction of each of the power stations, any waste disposal and decommissioning of the station at the end of its lifetime.

 

From these results it is obvious that even with the carbon emissions associated with mining of uranium, building the power station and disposing of the waste, nuclear power still emits far less greenhouse gases than coal or natural gas powered stations, the major forms of power generation in Australia. Renewable resource-powered stations such as wind, hydroelectric or geothermal still do emit less greenhouse gases however. So while there would be a considerable effect on carbon emissions by replacing coal or natural gas fired power stations with nuclear, further savings could potentially be made by developing new renewable powered stations.

 

So nuclear power stations do produce less CO2 than a coal fired plant, but what about radiation levels? Possibly contrary to popular belief, nuclear power stations release effectively no radiation. In fact a nuclear power station releases less radioactive material into the atmosphere during operation than a coal power station (INSERT LINK http://www.scientificamerican.com/article.cfm?id=coal-ash-is-more-radioactive-than-nuclear-waste) . The ash produced from burning coal contains small amounts of uranium and thorium, another radioactive substance, which is emitted into the atmosphere and can contaminate nearby land and water. This ash results in a coal fired power station releasing at least 100 times more radiation into the environment than a nuclear plant producing the same amount of electricity. However, to put it in context, the amount of radiation a human would be exposed to in a year of living near a coal power station is around 1/180th the levels that humans are exposed to each year normally just in background radiation. In other words, there is effectively no risk from radiation by living near either a coal plant or a nuclear plant.

 

There are many economic questions over nuclear power, and new more carbon friendly power generation technologies are either currently in development or coming online. Whether it is viable to go nuclear in Australia depends on these and other factors, including the requirement for extremely large amounts of water during the mining of uranium. One new technology which may be promising as an energy source is hydrogen power; however there are some pitfalls to that too. In the near future I’ll be blogging about one of the new technologies being developed which may make hydrogen power more attractive as an option.

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