The Relative Safety of the New Generation of Nuclear Reactors

by Marcel F. Williams

The Chernobyl nuclear disaster occurred on April 26th, 1986 when reactor number four at the Chernobyl electric power facility in the Ukraine had a chemical explosion. Human error combined with the poor construction and design of the facility caused the chemical explosions and fires that released a plume of highly radioactive fallout into the atmosphere. Thirty-five people who attempted to put out the fires at Chernobyl died shortly after the accident of radiation poisoning. However, the immediate evacuation of about 116,000 people from areas surrounding the reactor reduce the general population from exposure to high levels of radiation. A United Nations report determined that a total of 57 people died as a direct result of the radiation from the disaster. Additionally, the UN study predicted that over several years up to 4000 additional deaths could result from radiation exposure from Chernobyl. However, the latest UN report suggest that these numbers may have been overestimated. Additionally, the IAEA reports that there has been no solid evidence of any additional deaths related to the Chernobyl disaster.

It should be noted that the Ukraine has lost hundreds of people since the Chernobyl disaster, deaths not due to the nuclear industry but due to coal mine disasters. In China, more than 44,000 people died in coal mine diasters from 2000 to 2007. Even in the US, over 800 people died in coal mines from 1980 to 2007. Additionally, it is estimated that coal pollution kills over 30,000 people annually in the US and over 170,000 people worldwide die annually because of coal pollution.

Seven years before the Chernobyl nuclear accident, there was a core meltdown at Unit Two at the Three Mile Island nuclear power facility in the United States. However, contrary to Chernobyl, no member of the public was injured during the accident. That's because nuclear reactors in the US are safely housed in containment structures. The off-site radiation exposure during the Three Mile Island accident was 0.46 mSv which is substantially lower than a gastrointestinal X-Ray (2.2 mSv). About 50 mSv is the lowest dose at which there is any evidence of cancer being caused in adult human beings.

It should be noted that humans expose themselves to their own natural radiation, from the radioactive potassium in their bones, at about 0.39 mSv annually. Exposure to cosmic radiation in the US can range from 0.35 mSv to 1.2 mSv annually and exposure to terrestrial radiation can range from 0.30 mSv to 1.15 mSv. Additionally, humans are also exposed to an average of 2.0 mSv from radon in the atmosphere annually.

But when it comes to man made disasters in the 20th century, even the worse nuclear accident in human history is dwarfed by several other human caused events:

On December 20, 1987, the Philippine- registered passenger ferry, the MV Dona Paz, sank after colliding with the MT Vector oil tanker resulting in more than 4000 deaths. We all remember the substantial loss of life aboard the Titanic back in April 1912, but this is cited as the worst peace-time maritime disaster in history.

In response to a fog induced cold snap in London back in December of 1952, the people of London began to burn a lot more coal. This resulted in polluted air being trapped by an inversion layer formed by the dense mass of cold air. The 'Great Smog' initially killed some 4000 people with an additional 8000 dieing several months later.

The Bhopal India chemical disaster started on December 3rd, 1984. A Union Carbide subsidiary accidentally released 42 tonnes of toxic methyl isocyanate (MIC) gas from a pesticide plant. More than 8000 people died within two weeks time. Some estimate the people still suffering from this disaster may raise the death toll to over 15,000 people.

On August 8th, 1975, the breach of the Banqiao Dam in China released 700 million cubic meters of flood water in just 6 hours, wiping the Daowencheng Commune completely off the map, killing all 9,600 of its citizens. Approximately 26,000 people died from the flooding and an additional 145,000 died from the resulting famine and epidemics in the Henan Province area. 5,960,000 buildings collapsed affecting 11 million residents.

Now that the US and the world is experiencing a new energy and climate change crisis, nuclear power is being looked at as a possible long term solution to our energy and environmental problems. But how safe are current nuclear reactors? And how safe are the new generation of fission reactors such as the NRC certified AP1000?

The frequency in which a single nuclear reactor is likely to experience damage to its core (a nuclear meltdown) is referred to as "core damage frequency". The frequency in which a single nuclear reactor with a containment structure is likely to expose the surrounding environment with significant amounts of radioactive material after a major core damage event is referred to as "large release frequency".

There are less than 450 commercial nuclear reactors currently operating in the world. But what would the relative safety consequences be if our planet-- dramatically increased-- the number of fission reactors? What are the statistics?


Frequency of Core Damage in Current US Nuclear Reactors
(2 × 10⁻⁵ reactor years)

1 reactor -- once every 50,000 years
10 reactors -- once every 5,000 years
100 reactors -- once every 500 years
1000 reactors -- once every 50 years
10,000 reactors -- once every 5 years


Frequency of Core Damage for ABWR
(2 x 10^-7 reactor years)

1 reactor -- once every 5 million years
10 reactors -- once every 500 thousand years
100 reactors -- once every 50,000 years
1000 reactors -- once every 5000 years
10,000 reactors -- once every 500 years


Frequency of Core Damage for ACR 1000 (CANDU)
(3 x 10^-7 reactor years)

1 reactor -- once every 3.3 million years
10 reactors -- once every 330 thousand years
100 reactors -- once every 33,000 years
1000 reactors -- once every 3300 years
10,000 reactors -- once every 330 years


Frequency of Core Damage for ESBWR
(3 x 10^-8 reactor years)

1 reactor -- once every 33 million years
10 reactors -- once every 3.3 million years
100 reactors -- once every 33o,ooo years
1000 reactors -- once every 33,000 years
10,000 reactors -- once every 3300 years


Frequency of Core Damage for AP 1000
( 5.09 x 10^-7 reactor years)

1 reactor -- once every 2 million years
10 reactors -- once every 200,000 years
100 reactors -- once every 20,000 years
1000 reactors -- once every 2000 years
10,000 reactors -- once every 200 years

Frequency of Large Release of Radioactive Material for AP 1000
(6 x 10^-8 reactor years)

1 reactor -- once every 17 million years
10 reactors --- once every 1.7 million years
100 reactors --- once every 170 thousand years
1000 reactors -- once every 17,000 years
10,000 reactors -- once every 1700 years


There are slightly more than 100 commercial nuclear reactors in the US. And all were upgraded for safety after the Three Mile Island incident . So at current power production levels, the probability of another meltdown in the US would be one in 500 years. And if we conservatively assume that a large release of radiation due to containment structure failure might occur perhaps once in every 5 core damage incidents, then we could expect the general public in the surrounding environment might be put in danger, once every 2500 years.

But as shown above, the safety of the new generation of reactors has been substantially improved. So that even if we powered our entire human civilization with about 10,000 AP 1000 (1,100 MWe) nuclear reactors, we could expect a meltdown just once every 200 years with a significant breach of containment occurring just once every 1700 years. And if Chernobyl is the best example of the worse case scenario for commercial nuclear power then we can expect less than 60 people will die when such a breach of containment does occur perhaps a few thousand years from now. Wow!

Possible future commercial reactors such as the Pebble Bed Modular Reactor (PBMR) and subcritical reactors like the ADS (Accelerator-Driven Systems), of course, would have a zero possibility of meltdowns. And such inherently safe reactors could compliment or eventually replace some of the new extremely safe reactor systems within the next 20 or 30 years.

References and Links

1. G. Olah, A. Goeppert, and G. Prakash, (2006) Beyond Oil and Gas: The Methanol Economy, Wiley-VCH Verlang, Weinheim, Germany

2. AECL ACR-1000 - Technical Report

3. AP 1000

4. Nuclear Safety

5. Three Mile Island Accident

6. Chernobyl disaster

7. U.S. coal mining deaths: 1990-2007

8. The Catastrophic Dam Failures in China in August 1975

9. After 30 years, secrets, lessons of China's worst dams burst accident surface

10. Subcritical Reactors

New Papyrus 2009