Archive for the ‘Energy’ Category

The 2011 World Solar Challenge has been run and won

October 20, 2011

They started under clear skies and blazing heat and finished in steady rain, but the winner of the 2011 World Solar Challenge has been decided. After 4 days of travelling, Tokai University (Japan) crossed the finishing line north of Adelaide today in the lead.

Tokai University's car crossing the line surrounded by team members

In the closest finish in the history of the WSC, mere minutes separated Tokai and second placed Nuon Solar Team from the Netherlands. Third placegetters University of Michigan (USA) were themselves only a short distance behind. The close finish is remarkable given the distance travelled and time spent on the road. Ashiya University, of Japan, and Team Twente, also of the Netherlands, are further behind vying for fourth place and expected to finish Friday, as is Team Aurora of Australia, not far behind Ashiya and Twente.

The World Solar Challenge is an epic 3000km solar car challenge, running down the length of Australia from Darwin to Adelaide. With unlimited regulations it is likely all the cars would be able to exceed the road speed limit and run for extended periods of time. Instead, the regulations deliberately limit battery sizes and solar collection area to prevent the ability for the cars to run at maximum speed for hours on end and hence to help promote the development of more efficient solar collector units and motors.

The main differentiator between the cars is the ability of the solar cells to collect energy from the sun and convert it into electricity. With limited battery sizes, the energy which can be held on board the car isn’t enough to allow unrestricted running. Instead, the speed of the car is dictated by the combination of the amount of energy being collected from the solar panels, and the efficiency of the motor using that energy. The faster a car runs, the more energy it uses and hence the more energy it needs to collect to replace that used. Quite simply, if a car’s solar panels aren’t efficient in collecting energy to replace that being used, the car will run out of electricity. So a balance needs to be found between energy collection and expenditure, with cars more efficient at collecting and using energy able to run at higher speeds.

Further adding to the challenge, running of the cars is restricted to certain hours of the day, with cars required to hold at positions overnight. To ensure that the cars do maintain these hold positions, and stay within the legal speed limits, a sophisticated tracking system is employed to monitor the progress of each team. This ‘Mission Control’ was this year based in the Science Exchange in Adelaide.

This year’s race was never going to break any records with the challenge suspended for several hours due to bushfires close to the race route. There was also another dramatic development on day 4 when a car from Team Philippines, having been parked for repairs to its battery system, suffered an explosion in its battery packs. Thankfully, no one was injured.

Another challenge faced by the teams competing in the World Solar Challenge are the outsized road trains which Australian highways are famous for. These extremely long and wide trucks normally require traffic coming the other way to pull off the highway to allow the truck to pass. However, according to Bruno Moorthamers from Nuon in an interview with The Register, a solar car’s steering doesn’t allow this manoeuvre. Instead, Bruno said he has to drive “a little under” the overhanging loads of the trucks.

Despite crossing the official finishing line Thursday afternoon, a late developing fault meant that Nuon would not enter Adelaide city until the following day, meaning that celebrations in the Victoria Square ceremonial finishing line were reserved for Tokai. Dutch supporter groups hoping to cheer home Nuon and Twente were left instead to congratulate the victorious team and wait for their teams to arrive on the Friday. Tokai certainly celebrated in the rain, and definitely showed their excitement at having won such a hard-fought challenge.

Tokai team members celebrating at the finish

Celebrating with sake

Zoz Brooks from the Discovery Channel meets the driver who brought the Tokai car across the line.

The winning Tokai University team

The team celebrates by jumping into the Victoria Square fountain.

The Tokai team congratulate each other

Team Twente supporters at the finishing line

Supporters of Nuon Solar Team at the finishing line

Tokai celebrate in the Victoria Square fountain

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Nuclear Power – Dealing with waste and carbon emissions

March 4, 2011

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.

Nuclear power – How a nuclear reactor produces electricity

March 1, 2011

News reports last week suggested that members of the political party currently in government in Australia – the Australian Labor Party – are recommending a debate about the future of nuclear power generation and a rethink to their opposition to nuclear energy. While Australia does not have any nuclear power stations, there are around 450 operating stations worldwide. France, for example, generates around 75% of its power from nuclear stations. If Australia is going to start a debate about nuclear power, it makes it a fitting time to look at just how a nuclear power reactor works, what nuclear waste really is, and whether they as carbon friendly or unfriendly as people think.

 

How a nuclear power station works

The key factor for a nuclear reaction in a power station is Uranium, a naturally occurring chemical. Uranium is found in many forms, the most common of which is called Uranium-238, which makes up around 99% of total Uranium. The type used for generating nuclear power however, Uranium-235, only makes up around 0.7% of total Uranium.

 

In a nuclear power station, Uranium-235 is bombarded with extremely small particles called neutrons. When Uranium-235 is struck by a neutron, it absorbs it and becomes extremely unstable, causing it to split apart. This splitting of Uranium-235 releases a large amount of energy as, as well as three more neutrons and a large amount of radioactivity. The actual splitting is referred to as fission.

A neutron (blue particle at the top) strikes a Uranium-235 atom, causing instability and splitting into two smaller atoms. This splitting releases energy and three neutrons.

 

This reaction occurs underwater in a nuclear power station. This is for two reasons: firstly to control the speed of the neutrons, and secondly to keep the temperature of the Uranium under control. The energy released from the Uranium-235 splitting heats the water surrounding it – this heated water is then used as a heat source to boil another separate vessel of water and produce steam. This steam is then used to turn electricity generators, producing the electricity. In essence, a nuclear power station is just an extremely large super-powered kettle, boiling water to produce steam.

 

Schematic of a nuclear reactor. The uranium-235 fuel rods (6) heat water which is then piped (7) to a separate vessel (8). In this vessel, cold water (13) is heated and the resulting steam (12) is used to turn power turbines (not pictured). The reactor water is returned to the reaction vessel (10).

 

The neutrons released from the reaction continue to travel onwards until they strike more Uranium-235, causing the same reaction over and over – a chain reaction. In an ideal situation, one of those three neutrons will strike another Uranium-235 atom, and one of the three neutrons released from that fission reaction will strike another. This situation, where only one out of three neutrons causes another fission reaction is very stable, for every neutron causing a reaction, there is only one resulting neutron causing another reaction, meaning the number of reactions happening does not increase or decrease.

 

The major factor controlling how many resultant neutrons strike another Uranium-235 atom is the amount of Uranium-235 available to act as a target. If there is less Uranium-235 there are less targets for the neutrons to strike and it is called “subcritical”, the number of reactions will reduce and the energy production will diminish. If there is too much Uranium-235 there are many targets for the neutrons and it is called “supercritical”, more than one neutron may strike another Uranium-235, increasing the number of reactions occurring and increasing the amount of energy being released. If this is not controlled, the amount of energy can continue to increase until it causes an explosion. When only one neutron strikes another Uranium-235 it is called “critical mass”, with no increases or decreases of the energy produced.

 

In practice, a nuclear power station will actually be supercritical, it will have more Uranium-235 than required to keep the one-to-one ratio. The levels of the reactions are controlled using control rods made from a mixture of metals. These control rods are pushed into the water and literally soak up the neutrons being released by the splitting of Uranium. By adding more control rods the number of follow-up reactions is reduced by removing more neutrons. Removing control rods has the opposite effect, with more neutrons being allowed to create reactions. Using these control rods the energy production can be closely controlled, keeping the nuclear reactions at a stable level, and also controlling the amount of steam produced and electricity output from the station. This allows the station to increase or decrease electricity production in response to demand.

 

Control rods controlling the nuclear reaction. On the left, control rods are used to reduce the nuclear reaction by preventing neutrons from causing chain reactions. On the right, the control rods have been withdrawn, allowing more neutrons to cause fission and increased energy production. These control rods are capable of completely stopping the nuclear reaction, and can be used to shut-down the nuclear station almost instantly if the chain reactions increase out of control.

 

As mentioned earlier, Uranium-235 only makes up around 0.7% of total Uranium. However, for use in a power station the amount of Uranium-235 needs to be around 2-3%. To increase the levels of Uranium-235, before being sent to the power station Uranium is enriched to increase the proportion of Uranium-235. After processing the Uranium is formed into pellets approximately 2.5cm long, with the normal lifespan of these pellets in a nuclear power station around 3-5 years, after which the amount of Uranium-235 remaining in the pellet has reduced to a level which is no longer a critical mass. Following this time, the rods are removed from the power generator and become waste.

 

As a point of comparison – nuclear weapons require at least 90% Uranium-235 to be effective. This means that Uranium power station fuel is woefully insufficient to be used as a weapon without extensive processing.

 

Nuclear power stations are extremely safe when designed and operated correctly. However, they do produce toxic waste, and the next article will look at this waste and ask the question whether nuclear power is as carbon friendly as its supporters believe.