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[[Image:Nuclear power defense in depth.png|280px|thumb|This diagram demonstrates defense-in-depth in modern nuclear power plants. Current plants may have some or all of these defenses, the defenses vary depending on the type of plant, the nation constructing them, the use (civilian, military, naval vessels) and the generation the plant is from.

1st layer of defense is the inert, ceramic quality of the uranium oxide itself.

2nd layer is the airtight zirconium alloy of the fuel rod.

3rd layer is the reactor pressure vessel made of steel more than a dozen centimeters thick.

4th layer is the pressure resistant, airtight containment building.

5th layer is the reactor building or in newer powerplants a second outer containment building.]]

Nuclear safety covers the actions taken to prevent nuclear and radiation accidents or to limit their consequences. This covers nuclear power plants as well as all other nuclear facilities, the transportation of nuclear materials, the use and storage of nuclear materials for medical, power, industry, and military uses. In addition, there are safety issues involved in products created with radioactive materials. Some of the products are legacy ones (such as watch faces), others, like smoke detectors, are still being produced.

Nuclear weapon safety, as well as the safety of military research involving nuclear materials, is generally handled by separate agencies than civilian safety, for various reasons, including secrecy.


Many nations utilizing nuclear power have special institutions overseeing and regulating nuclear safety.

Internationally the International Atomic Energy Agencymarker "works for the safe, secure and peaceful uses of nuclear science and technology."

Civilian nuclear safety in the U.S. is regulated by the Nuclear Regulatory Commission (NRC). The safety of nuclear plants and materials controlled by the U.S. government for research, weapons production, and those powering naval vessels, is not governed by the NRC.

In the UK nuclear safety is regulated by the Nuclear Installations Inspectorate (NII) and the Defence Nuclear Safety Regulator (DNSR).


Nuclear power plants are some of the most sophisticated and complex energy systems ever designed, and critics have seen nuclear power as a dangerous, expensive way to boil water to generate electricity. Proponents have argued that much of that complexity is due to redundancy of systems, extensive backups, and the defense in depth strategy of design. However, any complex system, no matter how well it is designed and engineered, cannot be deemed failure-proof. This is especially true if people are required to operate controls that dictate how the system functions. Stephanie Cooke has reported that:
The reactors themselves were enormously complex machines with an incalculable number of things that could go wrong. When that happened at Three Mile Islandmarker in 1979, another fault line in the nuclear world was exposed. One malfunction led to another, and then to a series of others, until the core of the reactor itself began to melt, and even the world's most highly trained nuclear engineers did not know how to respond. The accident revealed serious deficiencies in a system that was meant to protect public health and safety.
A fundamental issue related to complexity is that the nuclear power systems have an exceedingly long stay time. The timeframe involved from the start of construction of a commercial nuclear power station, through to the safe disposal of its last radioactive waste, may be 100-150 years.

Failure modes of nuclear powerplants

There are concerns that a combination of human and mechanical error at a nuclear facility could result significant harm to people and the environment:
Operating nuclear reactors contain large amounts of radioactive fission products which, if dispersed, could pose a direct radiation hazard, contaminate soil and vegetation, and be ingested by humans and animals. Human exposure at high enough levels can cause both short-term illness and death, and longer-term deaths by cancer and other diseases.

Nuclear reactors can fail in a variety of ways. Should the instability of the nuclear material generate unexpected behavior, it may result in an uncontrolled power excursion. Normally, the cooling system in a reactor is designed to be able to handle the excess heat this causes, however, should the reactor also experience a loss-of-coolant accident, then the fuel may melt, or cause the vessel it is contained in to overheat and melt. This event is called a nuclear meltdown. Because the heat generated can be tremendous, immense pressure can build up in the reactor vessel, resulting in a steam explosion such as happened at Chernobyl.

Intentional cause of such failures may be the result of nuclear terrorism.

Hazards of nuclear material

Nuclear material and materiel may be hazardous if not properly handled or disposed of. Experiments of near critical mass sized pieces of nuclear material can pose a risk of a criticality accident. David Hahn serves as an excellent example of a nuclear experimenter who failed to develop or follow proper safety protocols. Such failures raise the specter of radioactive contamination.

Even when properly contained, fission by-products which are no longer useful generate radioactive waste, which must be properly disposed of. In addition, material exposed to neutron radiation — present in nuclear reactors — may become radioactive in its own right, or become contaminated with nuclear waste. Additionally, toxic or dangerous chemicals may be used as part of the plant's operation, which must be properly handled and disposed of.

Vulnerability of plants to attack

Nuclear power plants are generally (although not always) considered "hard" targets. In the US, plants are surrounded by a double row of tall fences which are electronically monitored. The plant grounds are patrolled by a sizeable force of armed guards. The NRC's "Design Basis Threat" criteria for plants is a secret, and so what size attacking force the plants are able to protect against is unknown. However, to scram a plant takes less than 5 seconds while unimpeded restart takes hours, severely hampering a terrorist force in a goal to release radioactivity.

Attack from the air is a more problematic concern. The most important barrier against the release of radioactivity in the event of an aircraft strike is the containment building and its missile shield. Current NRC Chairman Dale Klein has said "Nuclear power plants are inherently robust structures that our studies show provide adequate protection in a hypothetical attack by an airplane. The NRC has also taken actions that require nuclear power plant operators to be able to manage large fires or explosions—no matter what has caused them."

In addition, supporters point to large studies carried out by the US Electric Power Research Institute that tested the robustness of both reactor and waste fuel storage, and found that they should be able to sustain a terrorist attack comparable to the September 11 terrorist attacks in the USA. Spent fuel is usually housed inside the plant's "protected zone" or a spent nuclear fuel shipping cask; stealing it for use in a "dirty bomb" is extremely difficult. Exposure to the intense radiation would almost certainly quickly incapacitate or kill anyone who attempts to do so.

Risk assessment

The AP1000 has a maximum core damage frequency of 5.09 x 10-7 per plant per year. The Evolutionary Power Reactor (EPR) has a maximum core damage frequency of 4 x 10-7 per plant per year. General Electric has recalculated maximum core damage frequencies per year per plant for its nuclear power plant designs:
BWR/4 -- 1 x 10-5
BWR/6 -- 1 x 10-6
ABWR -- 2 x 10-7
ESBWR -- 3 x 10-8

Enforcement organizations

Nuclear accidents

See also

External links


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