Archive for March, 2011

Thoughts of a former Chief Scientist

March 16, 2011

John Stocker, previously chairman of the CSIRO and now a private industry scientific advisor, served as Chief Scientist of Australia from 1996 to 1999. He provided his thoughts on the role of the Chief Scientist and the future of the position.

 

“At the heart of the issue lies the need for the government to make evidence-based policy. And you just have to look at the huge issues facing governments everywhere, and ours in particular at the moment, ranging all the way from decisions on public health, to water use, to energy, to climate issues, to marine eco-systems, vaccination policy, and the role of Australia internationally in big science. We are a small country in population sense, but we punch hugely above our weight in some areas. And they all depend on decision makers having access to the best evidence, and also access to proper debate about the uncertainties that always underpin any evidence.  And so I think the Chief Scientist has a unique role.”

 

“I think the point that initially the Chief Scientist was administratively within the Department of Prime Minister and Cabinet is an important point, and I think the closeness of the Chief Scientist to the Prime Minister, and the likelihood that the Prime Minister is going to say, “Gees, we’ve got an issue here, we need someone to talk to, wheel in the Chief Scientist,” would be greatly facilitated by going back to that model, rather than have the Chief Scientist imbedded in some other bureaucracy.”

 

John also suggests tailoring the role to the ideal appointee, rather than choosing an appointee who best fits a pre-designed position. “I think to decide up front that anybody who can’t do the job full-time is excluded is a silly decision, and that it may well be under some circumstances beneficial to have someone who is still practicing, active scientist, providing this independent advice to government.  And so I think it forces the course, you choose the best person you can find in the nation who is likely to be able to meet these really, really tough criteria, and then you design the system around that person.”

 

The Chief Scientist plays a vital role in advising government policy, and, when a new appointee is made they will need to continue this work. While the impact of the Chief Scientist has arguably been diminished recently, governments need to utilise all their resources to make the best informed policy decisions, and the Chief Scientist has, and still does, provide extremely important independent, non-political input into the direction of future government decisions.

 

Thanks to John Stocker from Foursight Associates.

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Who or what is a Chief Scientist?

March 15, 2011

Australia’s Chief Scientist, Penny Sackett, has made news recently by abruptly leaving her post. Last week marked her last days in the role, and her departure leaves the position vacant. However not many people realise that Australia has a Chief Scientist, and even less understand what role the Chief Scientist plays.

 

The Chief Scientist of Australia

Australia has had a Chief Scientist since 1989 when Ralph Slatyer, an ecologist, was appointed to the position. He was succeeded in 1992 by biologist Michael Pitman, with both men serving the role full-time and accountable to the Department of the Prime Minister. Being accountable to the Department of the Prime Minister allowed both men to provide input across multiple portfolios, however in 1996 the position was moved to become part of the Department of Innovation, Industry, Science and Technology (DIISR) and reduced to a part-time position. John Stocker, an immunologist from the CSIRO was appointed at this time, followed by Robin Batterham, then Jim Peacock. Astronomer Penny Sackett was appointed in 2008 when the role returned to a full-time position.

The main role of the Chief Scientist is to act as an advisor to the government on scientific and technology issues. In addition to this direct advisory role, the Chief Scientist is also involved in numerous committees, for example the Research Quality Framework, the National Research Priority Standing Committee and the Australian Climate Change Science Framework Coordination Group, amongst many others. The Office of the Chief Scientist also provides the secretarial service to the Prime Minister’s Science and Engineering Innovation Council, and the Chief Scientist him or herself holds the position as Executive Officer of that group. Through this group the Chief Scientist can greatly influence future policy decisions, in addition to their direct advisory role to the Prime Minister. For example, the Square Kilometre Array, effectively a giant telescope, was one instance when this council convinced policy makers to become involved in this international project.

 

The changing of the role from full-time to part-time and back to full-time, and also the move of the role from the Department of the Prime Minister to DIISR has slightly changed the effectiveness of the Chief Scientist. Positioning the Chief Scientist in DIISR potentially restricts their ability to provide input across portfolios and the advice they can provide to government, while the change in time commitments may also restrict their abilities. Whereas a full-time role allows the position-holder to concentrate solely on the role, a part-time position may allow them to keep a foot in the field and remain current in the research occurring. According to Anna-Maria Arabia from the Federation of Australian Scientific and Technological Societies and a former political advisor “I think each of those issues in terms of the terms of engagement, accountability and where the Chief Scientist and his or her office sits are all useful in determining the input that a person holding that position can have.”

 

Thomas Barlow, a former government advisor and a renowned corporate strategist agrees that the changes to the role have affected the abilities of the Chief Scientist. “If I had to choose between a part-time and a full-time position, I would tend to lean towards a part-time position.” He points to the need for the Chief Scientist to remain a practising scientist to retain credibility in the scientific community and not being perceived as a part of the government bureaucracy, and that with a full-time Chief Scientist “you end up with a Chief Scientist who, to an outsider, becomes seen as a spokesperson for the government, rather than an advisor to the government. And I think within the government, a Chief Scientist in a bureaucratic full-time role is very easily seen as part of the bureaucracy rather than as a part of the constituency… politicians will tend to listen more to their constituents than they do to their bureaucrats.”

 

International models of the Chief Scientist

It is interesting to compare the Australian model of a Chief Scientist to those found overseas. Where Australia’s Chief Scientist works within in a government department, in the UK, which has had a Chief Scientist since 1964, the Chief Scientist is more like a personal advisor to the Prime Minister and Cabinet. The Chief Scientist also has more public exposure and is one of the government’s most visible experts. In addition to the Chief Scientist, each government department (with the exception of the Treasury) has their own chief scientific advisors which come together as part of the Chief Scientific Advisor’s Committee. This type of model ensures a greater coverage of scientific advice over multiple portfolios, and allows the Chief Scientist to act mainly as an advisor to the PM and Cabinet rather than part of departmental bureaucracy.

 

The United States model is also based on an advisor working for the President. The Office of Science and Technology was established in 1976, and their main role is to advise the President and his office staff on issues relating to science and technology. A second role is to ensure that policies of government departments are informed by sound science, and that this process is properly coordinated.

 

It is notable that the role in both the UK and US are both more tightly associated with the head of government than it is in Australia. This potentially gives the position more impact both in advice given to the head of government and also in its ability to advise policy across departments.

 

Tomorrow, the thoughts of a former Chief Scientist.

Thanks to Anna-Maria Arabia from FASTS and Thomas Barlow from Barlow Advisory

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.