Saturday, July 10, 2010

Aren't Nuclear Reactors Dangerous?

In June 1959, Niels Bohr pressed a switch to rapidly remove all the control rods from the first Inherently Safe Nuclear Reactor – the Triga. The reactor did not meltdown, but after a very brief power spike of a few thousandths of a second the reactor quieted down. If such a feat was attempted in a normal Pressurized Water Reactor, it would surely cause a catastrophic accident. The Triga is a very different kind of reactor, it is built on principles which guarantee safety by the laws of physics, not just engineering cleverness. Most nuclear reactor designs currently in use today, and most of our advanced nuclear designs are not Inherently Safe Nuclear Reactors. As we deploy more nuclear reactors, we should develop systems that are safe by the nature of the laws of physics. This should be our long term goal as a society for nuclear power. One design that is particularly promising in this regard is the Liquid Fluoride Thorium Reactor, it can be built to have passive safety guaranteed by the laws of physics. That design also has many other highly desirable features, such as high usage of nuclear fuel, low proliferation risk, and higher thermodynamic efficiency.

Even without Inherently Safe Nuclear Reactors, the nuclear industry has the best track record of all power producing industries as far as safety is concerned. There has been only one severe accident in the history of nuclear power usage that caused loss of life. This accident occurred at Chernobyl in the Ukraine, and resulted in the loss of 56 lives.

While the accident at Chernobyl was horrible and something we want to avoid in the future, it pales in comparison to the loss of life from other energy sources. Chernobyl was caused by what could be described as an unsafe experiment in reactor physics done by ill trained personal. The Chernobyl reactor was also an unsafe design that does not lose moderation when the coolant is lost. The Chernobyl reactor used graphite as a moderator, while western designs typically use the coolant itself as a moderator. When a design that uses the coolant as a moderator experience loss of coolant, the nuclear reaction slows and becomes less intense. The opposite happened in the Chernobyl reactor, and without the containment that is standard in Western designs there was release of radiation into the environment. We can definitely do better, and avoid this sort of accident in the future.

In the United States and the European Block, we have never had a commercial nuclear accident that caused the loss of life. There have been studies and analysis that considered the replacement of the Barsebäck nuclear reactor in Sweden with coal power. For the same generating capacity the study concluded with a high probability that around 200 lives per year would be lost by replacing one nuclear reactor with a coal fired plant producing the same energy output.

Here is a chart detailing deaths per terawatt hour:

One nuclear power plant typically produces 1 gigawatt continually. Over an entire year if run at 100% capacity it generates 8760 gigawatt hours of electricity, this can also be expressed as 8.76 terawatt hours.

The mean average number of deaths per terawatt hour for coal is 25 deaths for the European Union. The mean average number of deaths per terawatt hour of generating capacity for nuclear is 0.02 deaths (An ExternE report, a research project done in the European Union to determine the external costs for energy generated was the source for the numbers used in the following calculation.)

8.76 terawatt hours * 25 deaths per terawatt hours = 219 deaths per year from coal.

8.76 terawatt hours * 0.04 deaths per terawatt hours = 0.3504 deaths per year from nuclear.

The study makes a further statement that the risk of death from a nuclear accident was very unlikely and the risk of death from coal was very high, essentially 100%.

The chart above came from the following report available on the internet:

Additional information about the ExternE project in general is available at:

Nuclear power is the safest power producing technology we currently possess. To call nuclear power unsafe just does not make sense given the numbers. Additionally with basic fundamental research, we will only further improve the situation.

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