NUREG/BR-0164, Rev. 9 

June 2012

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NRC–Independent Regulator of 

Nuclear Safety

The U.S. Nuclear Regulatory Commission (NRC), created by Congress, 

began operating in 1975. Its mission is 

to regulate commercial and institutional 

uses of nuclear materials, including 

nuclear power plants. The agency succeeded the U.S. Atomic Energy Commission, which was responsible for 

both developing and regulating nuclear 

activities. Now, federal research and 

development, and nuclear weapons 

production are done by the U.S. 

Department of Energy.

The NRC’s overall responsibility is to 

protect public health and safety. Its 

main regulatory functions are to:

•	 establish standards

and regulations; 

•	 issue licenses for

nuclear facilities and 

users of nuclear materials; and 

•	 inspect facilities and

users of nuclear 

materials to ensure 

compliance with the 

requirements. 

These regulatory functions relate to both 

nuclear power plants 

and other uses of nuclear materials — such 

as nuclear medicine 

programs at hospitals, 

academic activities at 

educational institutions 

and research. They 

also relate to such 

industrial applications 

as gauges, irradiators and other devices that contain radioactive material.

The NRC places a high priority on 

keeping the public informed of its work. 

The agency maintains a Web site and 

has a Public Document Room at its 

headquarters in Rockville, Md. It also 

holds public meetings throughout the 

country.

WHY REGULATE?

The nuclear industry is strictly regulated because radioactive materials 

are potentially hazardous. Radioactive 

materials give off radiation, which can 

Regulatory functions relate to both nuclear power plants 

and other uses of nuclear materials — such as nuclear 

medicine programs at hospitals.
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be hazardous to people exposed to it 

in significant amounts. The amount of 

harm depends on the type and amount 

of radioactive material, the distance 

between the source of the radiation 

and a person, and the length of time a 

person is exposed to the radiation.

The risks can be reduced by certain 

actions. For example, the hazard is 

less if there is a “shielding” material 

like lead or concrete to block some of 

the radiation, if a person moves farther 

from the radiation source, or if the exposure time is reduced.

If radioactive materials are properly 

handled and regulated, they do not 

pose a significant risk to the public or 

to workers.

Radioactivity from natural sources is 

present throughout the world. People 

are continuously exposed to low-level 

radiation from certain materials in 

the earth and from cosmic rays from 

space. Exposure to natural radiation 

can be affected by geography and lifestyle. For example, 

flying in an airplane 

adds to overall 

exposure because 

of increased cosmic 

radiation at high 

altitudes. People 

also receive some 

radiation exposure 

from certain medical 

procedures, such 

as X-rays.

The NRC protects the public by setting limits on radiation exposure from 

the radioactive materials it licenses. 

It also requires those with licenses to 

use such material to take steps to keep 

exposures well below the limits.

NRC

ORGANIZATION

The NRC is headed by a five-member 

Commission. The Commissioners are 

appointed to five-year terms by the 

President, with confirmation by the 

Senate. One of the Commissioners is 

designated as Chairman by the President.

The NRC has about 3,300 employees 

and an annual budget of about $800 

million. About two-thirds of the NRC 

employees work in the agency’s headquarters in Rockville, Md. The rest 

work primarily out of four regional offices or at resident inspector offices at 

Regional Office (4)

Technical Training Center (1)

Headquarters (1)

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NRC Headquarters 

and Regional

Office Locations
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each commercial nuclear power plant 

and some fuel cycle facilities.

NRC

REGULATIONS

The NRC sets the rules that users 

of radioactive materials must follow. 

These rules are intended to protect 

workers using the radioactive materials 

and the general public from the potential hazards of radioactivity. NRC regulations are constantly reviewed and 

sometimes changed — or new regulations added — based on recommendations from the NRC staff. Members of 

the public and interested organizations 

can also request changes in regulations. The NRC wants to hear the 

views of the public, industry and other 

interested parties before new rules or 

changes are adopted.

REGULATORY

RESEARCH

As part of its mission, the NRC has a 

research program that provides independent information and expertise to 

support the NRC’s safety and security 

decisions and to study potential technical issues. Much of this research work 

is done by government laboratories, 

universities, and other research institutions under contracts with the NRC. 

Some examples of research subjects include: the long-term strength 

of various parts of a nuclear reactor; 

the impact of natural events, such as 

earthquakes on nuclear facilities; the 

transport of radioactive waste and its 

disposal; and the way workers react 

to instruments and systems in nuclear 

facilities. 

LICENSES

The NRC licenses all commercial 

nuclear fuel facilities that process and 

fabricate uranium into reactor fuel. 

Licenses for more than 100 commercial nuclear power plants and their 

operators also are issued by the NRC. 

Licenses for other uses of radioactive materials are issued either by the 

NRC or by state governments under 

NRC-approved programs. About 4,500 

licenses for radioactive materials are 

under the jurisdiction of the NRC, and 

about 17,000 are under the jurisdiction 

of those states known as Agreement 

States. Agreement States regulate 

certain radioactive materials under 

agreements with the NRC. The NRC 

and states also have regulatory oversight for certain radioactive materials 

that occur naturally or are produced by 

machines called particle accelerators.

In most cases, any organization or individual intending to have or use radioactive materials must obtain a license. 

There are some exceptions. Users of 

smoke detectors, which have a tiny radiation source inside them, do not need 

a license because the amount of material is so small that it does not pose 

a danger to public health. However, 

those companies that make these or 

similar items do need a license and are 

subject to NRC or Agreement States 

regulations.

A typical license identifies the type and 

amount of radioactive material that 

may be held and used. The license 

may also have certain restrictions. It 

would describe the location of use, the 

training and qualifications of workers, 

specific procedures for using the materials, and any special safety precautions required.
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POWER PLANT

LICENSES

The currently operating nuclear power 

plants had to obtain both a construction permit, which allowed the facility 

to be built, and an operating license, 

which allowed the facility to operate.

In 1989, the NRC adopted a streamlined licensing process. It allows for 

a single license, consisting of a combined construction permit and operating license, to be issued. This process 

also encourages the use of standard, 

pre-approved designs for future plant 

proposals. Another feature of the 

streamlined process is possible early 

approval of sites for nuclear plants. 

This new process allows for full public 

participation, and most issues to be 

resolved, before construction begins. 

Public hearings are held on certifying 

sites and issuing construction permits 

and operating licenses. Prior to its initial operation, a new nuclear plant must 

complete a series of tests and inspections.

Since 2000, several power companies 

have used the Department of Energy’s 

“Nuclear Power 2010” initiative to “try 

out” parts of the NRC’s new reactor 

licensing process. Following the passage of the Energy Policy Act of 2005, 

which included several sections on 

nuclear power, a number of utilities 

announced plans to build new plants 

using the streamlined licensing process. The NRC expects to be working 

on these applications for many years. 

These will be the first new licensing 

applications for nuclear power plants in 

about three decades.

Licenses for nuclear power plants are 

issued for 40 years. Some of the initial 

licenses expire by 2010. The NRC developed a process for issuing renewed 

licenses and ensuring the continued 

safe operation of those plants for an 

additional 20 years. License renewals 

have been approved for many plants 

and more requests are under review. 

Licenses for nuclear power plants can 

be changed and updated to reflect 

experiences within the industry or new 

requirements. When necessary, the 

NRC can impose new regulations or require changes in operating procedures 

or equipment to improve nuclear power 

plant safety.

In addition to licensing the facility, the 

NRC also licenses the people who 

operate the controls of the reactor. 

Licenses fall into two categories — 

senior reactor operator, which requires 

a level of training necessary to act as 

a control room supervisor, and reactor 

operator. Before getting a license, 

individuals must complete an extensive 

training program and pass several 

tests. Once licensed, the operators 

continue their training to maintain 

their qualification.

INSPECTIONS

On a regular basis, the NRC inspects 

all facilities it licenses — including 

more than 100 nuclear power plants 

in 31 states — to make sure they are 

meeting NRC regulations, the terms 

of their licenses and orders issued by 

the NRC. The breadth of these inspections and how often they occur varies. 

For example, a nuclear power plant will 

be subject to many inspections each 

year, while a small medical or research 

facility using small amounts of radioactive materials might be inspected every 

few years. Normal inspections study 
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a sample of the work being done by a 

licensee. If problems are found or suspected, the inspector will focus on that 

work area in more detail.

For nuclear power plants and certain 

fuel processing facilities, inspections 

are done by:

•	 NRC resident inspectors, who are

stationed at the site on a full-time 

basis;

•	 NRC inspection specialists based in

regional offices and headquarters; 

and

•	 special team inspectors looking at

specific issues or potential problems.

The core of the NRC inspection program for nuclear power plants is carried out by the resident inspectors; at 

least two inspectors are assigned to 

each site.

The inspection specialists review 

plant security, emergency planning, 

radiation protection, environmental 

monitoring, plant 

equipment and 

systems, fire protection, construction activities, and 

other areas.

Each year, NRC 

specialists may 

conduct 10 to 25 

routine inspections 

at each nuclear 

power plant and 

several inspections 

at fuel facilities. 

The special team 

inspections may 

focus on a specific activity, such 

as maintenance or security, or a team 

may be sent to the facility to look at a 

specific operating problem or incident.

The NRC uses these inspections as 

well as objective performance indicators to assess the performance of 

each operating nuclear power plant. 

The NRC reviews the material quarterly, with formal reviews conducted in 

the middle and the end of a 12-month 

assessment period. This Reactor 

Oversight Process is based on “cornerstones” of safe operation. The plant 

assessments, performance indicators, 

inspection reports, and other evaluation documents are posted on the 

NRC’s Web site and available through 

the Public Document Room. Certain 

sensitive information — mostly related 

to nuclear facility security — may be 

excluded from the public version.

There is a range of actions the 

NRC can take if violations of NRC 

requirements are found during inspections. The basic enforcement action 

On a regular basis, the NRC inspects all facilities it licenses.
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is issuing a notice of violation, which 

requires the licensee to correct the 

problem and take steps to keep it from 

happening again. Serious and/or deliberate violations can result in fines. 

The largest fine the NRC has imposed 

to date was $5.45 million against the 

Davis-Besse nuclear power plant in 

2005.

If there are serious questions about the 

safety of NRC-licensed activities, the 

NRC requires the activities be stopped 

or an individual removed from work 

involving NRC-licensed materials. The 

NRC may modify, suspend, or revoke 

a license at any time. If the NRC stops 

licensed activities, they cannot begin 

again until the problems are fixed. A licensee or individual subject to a fine or 

an order can ask for a hearing before 

the NRC.

On occasion, the NRC receives allegations of safety problems or wrongdoing 

involving misconduct by licensees or 

their contractors. Allegations of possible criminal activities are handled by 

NRC professionals. These investigations may result in civil enforcement 

action or criminal prosecution. While 

the NRC is not dependent on allegations of safety problems to meet its 

responsibilities, the knowledge of thousands of employees working in NRCregulated activities provides valuable 

insights into the day-to-day practices of 

licensees. The NRC encourages employees working in regulated activities 

to raise safety concerns.

THE NUCLEAR 

FUEL CYCLE

The nuclear fuel cycle (shown below) 

has several steps. It begins when 

uranium ore mined from the earth is 

milled or processed to produce uranium concentrate. This concentrate is 

called “yellowcake.” The yellowcake is 

converted into uranium hexafluoride 

gas at a special facility and loaded into 

cylinders. Next, the cylinders are sent 

to an enrichment plant, where uranium 

is enriched for use as reactor fuel. The 

enriched uranium is then converted 

into oxide powder and made into fuel 

pellets (each about the size of a fingertip). These are loaded into metal fuel 

rods about 12 feet long. Rods are bundled into reactor fuel assemblies at a 

fuel fabrication facility. The assemblies 

The nuclear

fuel cycle







	 

	



		







	 

­	

	

	

 	­		
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of various sizes are then transported 

to nuclear power plants or non-power 

research reactor facilities.

Seven major fuel fabrication and production facilities are licensed to operate in the United States and two enrichment facilities are regulated by the 

NRC. A third enrichment facility was 

licensed in June 2006 and is under 

construction and the licensing review 

for a fourth enrichment facility is nearly 

complete. Because they handle radioactive material, these facilities must 

take special precautions to protect the 

public and workers. The facilities also 

must prevent the material from being 

stolen or diverted for use by terrorists. The NRC licenses and regularly 

inspects these plants to ensure they 

operate safely.

HOW A NUCLEAR 

POWER PLANT 

WORKS

Power plants change one form of energy into another — that is, heat is 

turned into electricity. Some plants may 

use the energy from wind, falling water 

or the sun or burn coal, oil or gas to 

generate electricity. A nuclear power 

plant uses energy from uranium to produce electricity. 

The heat — regardless how it’s produced — is normally used to heat 

Energy is released when an atom splits into smaller pieces. These smaller pieces strike 

other atoms, releasing more energy. This continuous splitting of atoms in a reactor is 

called a chain reaction.

NEUTRON

NUCLEUS

FRAGMENT

NEW

NEUTRON

NUCLEUS
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water to the boiling point and produce 

steam. This steam is then carried by 

pipes to a turbine, which has a series 

of fan blades on a shaft. The force of 

the steam pushes against the blades 

and turns the turbine.

The turbine is connected to a generator. As the turbine shaft spins, the 

generator turns and produces electricity. This electricity is carried by wires 

to homes, businesses and institutions. 

Electricity is one of the few forms of 

energy that can easily be moved from 

one place to another. Electrical energy 

can be produced in large quantities at 

one location and transported by wires 

to many different places.

We can see coal, wood, or gas burning — and know from experience that 

it produces heat. Nuclear energy 

in a nuclear power plant cannot be 

seen, and there is no burning of fuel 

in the usual sense. Instead, energy 

is given off by the nuclear fuel as 

certain types of atoms inside the 

fuel split into pieces. This energy is 

in the form of fast-moving particles 

and invisible radiation. As the particles and radiation move through 

the fuel and surrounding water, the 

energy is converted into heat. The 

heat is the useful energy resulting 

from the splitting of atoms.

Water in the reactor is heated by 

the nuclear reaction and the steam 

is carried off to spin the turbine to 

produce electricity.

URANIUM FUEL

The fuel of a nuclear plant is uranium, but only a certain type of 

uranium atom can be easily split to 

produce energy. This type of uranium atom — called uranium-235 — is 

less than 1 percent of natural uranium 

ore. The uranium ore must be purified 

and then processed to make it usable as fuel for reactors. In U.S. reactors the concentration of uranium-235 

must increase from 1 to about 3 or 4 

percent. This percentage is enough to 

allow a continuous splitting of uranium 

atoms — but much less than the percentage necessary for a nuclear weapon, which requires almost 100 percent 

pure uranium-235. The low percentage 

of uranium-235 in reactor fuel is one of 

the reasons a plant can never explode 

like an atomic bomb.

To increase the percentage of uranium-235, a process called enrichment 

is used. One method of enrichment 

uses a process called gaseous diffuControl Rod

Guide Tubes

Inlet

Nozzle

Outlet

Nozzle

Fuel

Assemblies
9

sion. This process heats natural uranium to form a gas, and then separates 

the lighter molecules of uranium-235 

from the heavier molecules of uranium-238 (another version of uranium). 

This separation is done by forcing the 

molecules through a membrane with 

tiny openings. Since the uranium-235 

is lighter, it moves through the membrane more easily, and the two gases 

can then be partially separated. This 

process increases the concentration of 

uranium 235.

When a uranium-235 atom is hit by a 

particle called a neutron, it splits, or 

“fissions,” and gives off energy in the 

form of radiation. It also gives off fastmoving pieces of the original atom, 

including neutrons, which can collide 

with another uranium-235 atom and 

cause it to split, too. A continuing series of these atomic splits, each triggering another one, is called a chain 

reaction.

Uranium-235 will split, or “fission,” 

spontaneously, but these spontaneous 

atomic splits aren’t 

frequent or reliable 

enough to use as an 

energy source. The 

neutrons fly away too 

fast and don’t usually cause the fission 

of another atom. The 

neutrons need to be 

slowed down so that 

they 

can collide with 

another uranium-235 

atom and continue 

the chain reaction.

Several types of 

materials can be 

used to slow down 

the neutrons. Most nuclear power 

plants (including all of those in the 

United States) use water as the material that slows down the particles and 

allows the chain reaction to continue.

To control the chain reaction, reactors 

have control rods. These rods can be 

inserted into the reactor to absorb the 

neutrons, which slows or stops the 

chain reaction.

TWO REACTOR 

TYPES

Two main types of reactors are in 

operation in the United States — the 

pressurized water reactor (PWR) and 

the boiling water reactor (BWR). About 

two-thirds of the reactors are PWRs, 

and the rest are BWRs.

The PWR is a two-stage system that 

keeps the water in the reactor under 

high pressure so that it does not boil. 

Pressurized Water Reactor (PWR)

Containment Structure 
10

Piping carries this 

heated water to large 

components called 

steam generators. The 

heated reactor water 

flows through thousands of tubes in the 

steam generator. The 

tubes are surrounded 

by a secondary water 

supply. This secondary water supply, 

which is not radioactive, boils and produces steam, which is 

carried away by pipes 

to spin the turbinegenerator.

The reactor cooling 

water then returns to the reactor to be 

reheated and recirculated to the steam 

generator, in a continuous loop.

The BWR is a single-stage system 

that allows the water in the reactor to 

boil and produce steam, which is then 

piped directly to the turbine generator.

In both types of reactors, once the 

steam loses its energy in spinning 

the turbine, it flows into a condenser. 

Because not all the heat energy in the 

steam can be converted into electricity, the leftover heat must be carried 

away by cooling water pumped through 

the condenser. The condenser contains thousands of tubes carrying cool 

water, which converts the steam back 

to water. The water is collected in the 

condenser and pumped back to be reheated, either in the reactor itself in a 

BWR or in a PWR’s steam generator.

The condenser cooling water is drawn 

from a lake, river, or ocean. This water does not actually pass through the 

reactor, but only through the condenser 

tubes to cool the steam after it goes 

through the turbine. There is no contact 

between the condenser cooling water 

and the reactor cooling water or the 

reactor components themselves. The 

reactor cooling water is contained and 

kept isolated from the environment.

This outside cooling water, heated as 

it passes through the condenser, is 

returned to its source. Many nuclear 

plants — as well as other types of 

power plants or industrial facilities — 

use cooling towers, cooling lakes or 

ponds, or other techniques to reduce 

the effects of discharging heated water directly back into the river, lake, or 

ocean. With cooling towers, the water, 

once cooled, is usually pumped back 

into the condenser to be used again 

to carry off heat. Only a small portion 

of the water is returned to the natural 

water source. To preserve the environment, the water returned to its source 

must be no more than a few degrees 

warmer than the source water.

Boiling Water Reactor (BWR)
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RADIOACTIVE 

BYPRODUCTS

Because the fission reaction produces 

radioactive materials, which can be 

hazardous, nuclear power plants have 

safety systems to protect workers, the 

public and the environment.

Radioactive materials must be used 

carefully because they produce radiation—a form of energy that can damage human cells and potentially cause 

cancer. The damage depends on how 

much radiation the cells were exposed 

to and for how long. Radiation can 

potentially cause cancer over long 

periods of time. 

A person can be exposed to radiation 

in two ways — internally and externally. 

Internal exposures happen if a radioactive material enters the body. External 

exposures happen when a person is 

too close to radioactive material without 

adequate protection (called shielding).

In the reactor, most of these hazardous radioactive substances — called 

fission byproducts — are trapped in the 

fuel pellets themselves or in the sealed 

metal tubes holding the fuel. However, 

small amounts of these radioactive fission byproducts, mostly gases, become 

mixed with the water passing through 

the reactor. Other impurities in the water are also made radioactive as they 

pass through the reactor. The water is 

processed and filtered to remove these 

radioactive impurities and then returned 

to the reactor cooling system. During 

normal plant operations, very small 

amounts of radioactive gases and liquids that do not pose a significant risk to

the public health are ultimately released 

to the environment under controlled and 

monitored conditions.

Radioactive materials lose their radioactive properties over time. This process is called radioactive decay. Some 

materials are short-lived and lose their 

radioactivity in seconds or minutes. 

Other radioactive elements take much 

longer — thousands of years in some 

cases — to lose their radioactivity.

The NRC has established limits for the 

release of radioactivity during routine plant operations. These limits are 

based on guidelines set by the U.S. 

Environmental Protection Agency, and 

by national and international standardsetting groups. The effects of very low 

levels of radiation are difficult to detect. 

But the NRC sets limits based on the 

conservative assumption that radiation 

exposures to the public should only 

be a small fraction of what is received 

from natural environmental radiation.

Nuclear plants typically release only 

traces of the amounts allowed during 

normal operations. A person spending 

a full year at a nuclear plant boundary 

would receive an additional radiation 

exposure of less than 1 percent of the 

radiation exposure everyone receives 

from naturally occurring radiation. 

(The average American receives 620 

millirems a year from natural environmental radiation and manmade radiation exposures, such as from medical 

X-rays.) Year-round exposure at the 

plant boundary is an additional 1 to 2 

millirems or less.

The NRC also sets limits for radiation 

exposure to people who work at nuclear plants and other facilities where radioactive materials are used. Radiation 

workers must wear devices that measure radiation to ensure their exposure 

is within the limits.

Routine operations at a nuclear power 

plant have only a very small environ-
12

mental impact. But because of the radioactivity 

in the reactor fuel, the 

plant must have effective 

safety systems to prevent 

an accident that could 

release a large amount of 

radioactivity. Such an accident is not likely, but the 

possibility leads to special 

care in designing, building and operating nuclear 

power plants.

REACTOR 

SAFETY 

SYSTEMS

A nuclear power plant is equipped with 

several different safety systems to prevent accidents and reduce their effects 

if one should occur, including:

•	 A system to quickly shut down a reactor and stop the chain reaction. 

•	 Systems that monitor reactor conditions, control reactor pressure and 

continue cooling the reactor fuel 

even if the reactor is shut down. 

•	 A system of barriers to contain radioactivity if it escapes from the reactor 

fuel in an accident. 

SHUTDOWN 

SYSTEMS

Each reactor has a system to insert the 

control rods into the reactor core within 

seconds to stop the fission reaction. 

This immediate shutdown — called a 

reactor “scram” or reactor “trip” — can 

be triggered by a reactor operator or 

by automatic controls that protect the 

reactor from any unusual conditions.

COOLING AND 

PRESSURE—

SAFETY SYSTEMS

When a reactor is operating, the heat 

energy from the fission reaction is 

carried off in the cooling water. That 

energy is used as steam to spin the 

turbine-generator, making electricity. 

A reactor shutdown stops the fission 

reaction, but heat is still generated by 

the natural decay of the radioactive 

fission byproducts, which build up in 

the reactor fuel. Much less heat is created at this point, but the heat is still 

high enough to damage the fuel if it is 

not cooled. As time passes after the 

reactor shutdown, the amount of heat 

produced in the fuel in the reactor core 

drops. But continued cooling of the fuel 

is still necessary. Each plant has both 

normal cooling and emergency cooling 

systems to ensure that the fuel remains 

cooled at all times.
13

The emergency core cooling system 

has pumps, valves and pipes that are 

separate from the normal cooling system. This system contains equipment 

that can pump at high pressure to send 

water into the reactor when the pressure inside is at the high levels maintained during operation. In addition, 

low pressure systems pump water at 

lower pressures, such as those that 

might occur if a cooling water pipe 

broke and allowed pressure inside 

the reactor to drop.

The reactor systems also have valves 

that can be opened to reduce pressure 

by releasing steam. These relief valves 

open automatically if pressure gets too 

high in the reactor system. Some of 

the valves can be opened using controls in the reactor control room. These 

pressure-reduction systems can also 

be used to reduce reactor pressure so 

that the low pressure cooling systems 

can work.

SAFETY SYSTEM 

POWER

Most of the safety systems are powered by electricity, although some 

pumps use steam to drive them in 

order to have an alternative source 

of power. Because of this reliance on 

electrical power, nuclear plants are 

required to have multiple sources of 

electricity.

Some nuclear plants use a portion of 

the power they generate to run. Those 

plants also have a system that allows a shift to “offsite” power, if that is 

needed. Other plants run only on offsite power. In addition, all plants have 

emergency diesel generators in case 

offsite power is lost. The generators 

are large enough to supply electricity to 

the critical safety systems for days.

The control and instrument systems for 

maintaining plant conditions normally 

use direct current (DC) electricity, the 

kind of power found in batteries. For 

these systems, large banks of batteries 

provide DC power if there is an interruption in the normal sources of electricity.

CONTAINING

RADIOACTIVITY

Nuclear power plants have three principal barriers to prevent the release of 

radioactivity — the sealed fuel rods, 

the reactor vessel and associated components, and the structure housing the 

reactor, called the reactor containment.

A serious reactor accident could damage the fuel rods, which form the first 

barrier, if there isn’t enough cooling. 

Overheated fuel rods could leak or 

break apart and eventually melt. Possible damage to the reactor cooling 

system piping could cause the second 

barrier to fail.

Even if the first two barriers fail, the 

reactor containment is designed to hold 

radioactive material that might otherwise be released to the environment. 

One type of reactor containment is a 

domed structure made of reinforced 

concrete with a steel lining. It is designed to withstand the pressures that 

might build up inside as steam and 

gases escape from the reactor during 

an accident. Another type of containment, called a pressure suppression 

containment, has a large water-filled 

pool to cool the steam and reduce the 

pressure buildup in the containment.
14

The NRC requires that the reactor containment be periodically tested to show 

it meets requirements to prevent leaks 

to the environment.

Reactor containment buildings are designed to handle many types of serious 

accidents. But it’s possible they may 

not be able to withstand the conditions 

that result from an extremely unlikely 

accident in which all cooling capability is lost in the reactor. Under these 

circumstances, the energy produced 

by the radioactivity remaining in the 

fuel could cause the fuel to melt. The 

melting fuel could eventually lead to a 

buildup of pressure that could cause 

radioactive gases to leak through seals 

and gaskets around the containment. 

The molten fuel could also damage the 

concrete base of the containment, possibly leading to a release of radioactivity. Even in these extremely unlikely 

cases, however, most of the long-term 

hazardous radioactive material would 

stay inside the containment structure.

In the only major commercial power 

reactor accident in the United States, 

the Three Mile Island accident in 1979, 

there was extensive fuel damage in 

the Pennsylvania reactor. Radioactive gases and contaminated cooling 

water filled the containment. Although 

some radioactivity was released to the 

atmosphere by an indirect route, the 

containment itself performed as designed and kept the radioactivity safely 

bottled up inside. The effectiveness of 

the containment was the major factor in preventing the release of large 

amounts of radioactive materials to the 

environment.

In 1986, a much more serious accident 

occurred at one of the Chernobyl reactors in the former Soviet Union. The 

reactor was very different from those 

used in the United States. The plant 

had no containment system like that of 

U.S. plants. The Chernobyl accident 

severely damaged the reactor core, releasing large quantities of radioactivity 

to the environment. Radioactive material was deposited in nearby countries, 

and radioactivity was detectable at very 

low levels in the United States.

EMERGENCY 

PREPAREDNESS

Although a major reactor accident is 

unlikely and each plant has safety systems to prevent or cope with an accident, there are additional measures in 

place to help protect public health and 

safety.

The first is special training given to the 

reactor operators in the handling of 

emergency situations. One of the lessons learned as a result of the Three 

Mile Island accident was that reactor 

operators needed to practice how they 

would handle emergencies. Detailed 

emergency operating procedures have 

been prepared and the operators have 

been trained to use them. In addition, 

most nuclear power plants use computer-based simulators for training in 

both routine and abnormal situations. 

These simulators are laid out just like 

the plant’s control room with all of the 

same controls and instrumentation. 

Computers let the operators practice 

dealing with emergencies.

The Three Mile Island accident also 

pointed out the need for improved 

planning by federal, state, and local 

governments to deal with possible 

reactor accidents. The NRC now requires emergency plans for evacuation 

or other actions to protect residents 
15

in areas near nuclear plants. These 

plans usually cover about 10 miles 

in all directions around each nuclear 

plant. The company has its own plan to 

notify government officials of a possible emergency and to provide them 

with information and recommendations. State and local governments 

have detailed plans for sheltering and 

evacuating residents if necessary. Federal emergency plans include federal 

personnel, equipment, and resources 

needed to respond to a nuclear power 

plant accident. The NRC would closely 

follow the handling of an accident by 

a company and afterward investigate 

the causes of the accident. The NRC 

also would coordinate with appropriate 

federal and state officials.

These plans are tested through emergency exercises that simulate a serious reactor accident. Company workers and government officials follow 

their emergency plans in gathering 

information, consulting with each other, 

and issuing instructions to the public. 

These emergency exercises sometimes include small-scale evacuation 

drills for schools, nursing homes, and 

other institutions.

The NRC must determine 

that there is reasonable 

assurance that evacuation 

or other steps can be taken 

to protect residents in the 

event of a major reactor 

accident. To make this 

determination, the NRC reviews the company’s plans, 

conducts inspections, and 

considers the assessment 

of state and local planning 

by the U.S. Department of 

Homeland Security (DHS).

SECURITY

Nuclear power plants have always 

been robust facilities with many security measures in place. After the terrorist 

attacks of Sept. 11, 2001, even more 

security measures were put in place. 

These measures are very strict in order 

to protect the plants from sabotage or 

attack.

The details of the added security measures are not available to the public 

because that might negatively affect 

the facility’s security. But the measures 

generally include:

•	 increased guard patrols,

•	 additional security forces and capabilities, 

•	 additional security posts,

•	 additional physical barriers,

•	 more restrictive controls on who can

come into the site, and 

•	 faster, more thorough checks of

employee backgrounds.
16

The NRC is also working with the 

U.S. Department of Energy, FBI, 

DHS, and other organizations to 

protect radioactive material that terrorists might try to make into a “dirty 

bomb.” The NRC is requiring greater 

control and tracking of this material, 

among other requirements.

NUCLEAR 

INSURANCE

In 1957, Congress established a system of “no-fault” insurance to provide 

liability coverage in the event of a 

major reactor accident. This insurance 

program, also known as the PriceAnderson Act, combines commercial 

insurance and self-insurance by the 

nuclear industry. Large nuclear plants 

are required to have the maximum 

amount of liability insurance that is 

commercially available, currently $300 

million. If there is an accident that 

causes damages higher than that, each 

licensed reactor will be assessed a 

share of the extra cost, up to $95.8 million, but no more than $15 million for 

any one reactor in a year.

With more than 100 commercial nuclear reactors in the United States, the 

combination of commercial insurance 

and industry self-insurance exceeds 

$10 billion. This is the total liability limit 

for an accident under the Price-Anderson Act. Congress, however, would 

consider the need for providing an 

additional source of funds should $10 

billion not be enough.

The Price-Anderson Act provides for 

liability insurance coverage for actual 

damages incurred by anyone affected 

by a major reactor accident. Besides 

the coverage for offsite public liability 

claims, the NRC requires that utilities 

maintain $1 billion in onsite property 

damage insurance to provide funds to 

deal with cleanup of the reactor site 

after an accident.

RADIOACTIVE 

WASTE DISPOSAL

During normal operations, a nuclear 

power plant generates two types of 

radioactive waste — high level and 

low level. High-level waste is the used 

fuel, often called “spent” fuel. Low-level 

waste includes such items as contaminated equipment, filters, maintenance 

materials, and resins used in purifying 

water for the reactor cooling system. In 

addition to nuclear power plants, other 

users of radioactive materials — such 

as hospitals — also generate low-level 

waste. Each type of waste is handled 

differently.

HIGH-LEVEL 

WASTE

Typically, the spent fuel from nuclear 

power plants is stored in water-filled 

pools at each reactor site and at one 

storage facility in Illinois. In addition, 

some companies have begun using dry 

cask storage for older spent fuel pending final disposal. In this way, spent 

fuel that has cooled in the pool for at 

least five years is stored in large metal 

and concrete containers placed on 

concrete pads or in concrete bunkers 

adjacent to the reactor facility. About 

one-fourth to one-third of the reactor 

fuel is removed and replaced every 

18 to 24 months.
17

When spent fuel is first removed from

the reactor, it is highly radioactive because it contains the fission byproducts

that were created within the reactor. 

Over time, these substances decay, 

leaving the longer-lived materials, which 

may be around for thousands of years, 

as the principal substances for disposal.

Special procedures are needed to 

handle spent fuel. The water in the 

spent fuel storage pool provides cooling and shielding from the radiation 

to protect workers in a nuclear plant. 

Concrete and steel in dry casks provide protection, too.

Although most of the spent fuel remains stored at individual plants, some 

spent fuel has been shipped to offsite 

interim storage facilities. These shipments have used heavily shielded shipping containers designed to withstand 

the conditions that might happen during a shipping accident. Spent fuel has 

been shipped by both rail and truck. 

The NRC certifies that each shipping 

container meets federal requirements, 

and the U.S. Department of Transportation sets the rules for actual transportation of the spent fuel.

Since some of the components in spent 

fuel remain hazardous for a long time, 

its permanent disposal requires a special disposal facility. The Department of 

Energy (DOE) had planned a permanent repository for spent fuel at Yucca 

Mountain, Nevada, but this effort was 

abandoned in 2010. The Secretary of 

Energy appointed a Blue Ribbon Commission on America’s Nuclear Future to 

develop recommendations for alternative strategies for managing spent fuel. 

In a draft report issued in July 2011, the 

Blue Ribbon Commission recommended 

establishing one or more centralized 

sites for extended storage of spent fuel 

until other solutions, such as disposal or 

recycling the fuel, can be developed.

The NRC is preparing to support and 

regulate whatever direction DOE and 

Congress decide to pursue for spent 

fuel management.

Since no DOE disposal site has been 

developed, many nuclear power plants 

are running out of room to store spent 

fuel in their storage pools. Nearly 60 

plants – including some that are permanently shut down – have transferred 

older spent fuel to safe interim storage in dry casks on site. This opens 

space in the spent fuel pool for cooling 

fuel that was removed from the reactor 

more recently.

Water-filled storage pool and dry cask storage
18

a DOE site is available, other plants, 

particularly the older ones, may run 

out of storage space in their spent fuel 

pools. More than 30 plants — including 

some that are permanently shut down 

— have transferred older spent fuel to 

safe interim storage in dry casks on 

site. This opens space in the spent fuel 

pool for cooling fuel that was removed 

from the reactor more recently.

LOW-LEVEL 

WASTE

Low-level radioactive waste, whether 

from a nuclear power plant or from 

other users of radioactive material, is 

shipped to licensed commercial disposal facilities. There, it is packaged and 

placed in burial trenches and covered 

with soil. Less than half of the waste 

volume is from nuclear power plants. 

The rest is generated by hospitals, 

research institutes, and other users of 

radioactive materials. The NRC has 

a classification system for low-level 

waste based on its potential hazards. 

There are specific disposal requirements based on the classification.

TRANSPORTATION

About 3 million packages of radioactive materials are shipped each year 

in the United States — by highway, rail, 

air, and water. Regulating the safety of 

these shipments is the joint responsibility of the U.S. Department of Transportation (DOT) and the NRC.

The federal regulatory system protects 

transportation workers and the public by 

setting performance standards for the 

packages. The system also sets limits 

on the radioactive contents and radiation 

levels for packages and vehicles. Information on radioactive shipments is provided by package marking and labeling, 

vehicle identification, and shipping papers

describing the materials.

DOT is responsible for radioactive 

shipments while the material is in transit. DOT also establishes shipping categories, sets the standards for labeling 

radioactive shipments, and establishes 

criteria for packages used for smaller 

quantities of radioactive materials. The 

NRC, which licenses the organizations 

shipping and receiving the radioactive 
19

materials, assures that its licensees 

comply with DOT shipping requirements. The NRC also establishes the 

requirements for designing and manufacturing packages for larger amounts 

of radioactive materials.

Typical of small-quantity shipments — 

using packages meeting DOT requirements — are radioactive materials for 

medical diagnostic tests and therapy. 

These shipments make up the major 

portion of all shipments of radioactive 

materials each year. For these shipments, packaging (classified as “Type 

A”) is used that is expected to withstand the rigors of normal transportation without being damaged.

The packages for larger quantities of 

radioactive materials are designed to 

withstand accident conditions without 

releasing their contents. These packages, designated as “Type B,” are 

used for shipping industrial irradiators, 

medical radiation therapy devices, and 

some radioactive wastes. These packages must survive a series of tests 

involving impact, puncture, heat, and 

submersion in water.

The spent fuel shipping cask is a specialized Type B package. It is used to 

transport used fuel from nuclear reactors. These large shipping casks are 

carried on trucks or rail cars. Like all 

Type B packages, they are sealed to 

prevent leaks and heavily shielded to 

minimize radiation levels.

In addition to safety requirements, 

the NRC imposes security requirements on shipments of spent fuel and 

on shipments of larger quantities of 

radioactive materials. These security 

measures include evaluating the route 

and having escort personnel and vehicles. State governments are notified 

in advance of spent fuel shipments 

and those large-quantity shipments 

of radioactive waste requiring Type B 

packages.

The regulatory system for transporting radioactive materials has successfully minimized the safety impact from 

accidents involving the shipments. 

Few accidents have occurred involving shipments of radioactive materials 

(averaging less than 50 out of 3 million 

packages shipped annually). Only a 

small number of those accidents have 

Site Decommissioning

Before After
20

involved any release of the radioactive 

contents. In these instances, radioactive 

contamination has been generally minor 

with no public safety consequences.

DECOMMISSIONING

Decommissioning is the term used for 

retiring a nuclear facility followed by 

cleanup to reduce radioactive contamination of the property. Nuclear power 

plants are licensed initially for a term 

of 40 years. Some plants may close 

before that time elapses.

Several nuclear power plants have 

been decommissioned, and some others are undergoing decommissioning. 

The NRC has adopted extensive regulations for dealing with the technical 

and financial issues associated with 

decommissioning.

During the operating life of a nuclear 

power plant, many plant components 

associated with the reactor become radioactive, either through contamination 

or as a result of the radiation from the 

fission reaction. For this reason, the 

decommissioning work must be done 

with care. Contaminated materials 

are shipped to a low-level radioactive 

waste disposal site for burial.

The NRC has identified two principal 

plans for decommissioning a nuclear 

power plant: immediate dismantling 

or safe storage for a period of 30 to 

50 years followed by dismantling. A 

third option, called entombment, may 

also be available in some cases. This 

involves sealing off radioactive components with concrete and steel. Entombment requires less maintenance 

and fewer security provisions than the 

storage option.

The storage and entombment methods 

allow the radioactivity to reduce over 

time. NRC studies show that after 50 

years radioactive decay would shrink 

the radioactively contaminated material to one-tenth of the original volume. 

Delay in dismantling a plant would also 

result in lower radiation exposures to 

the workers involved.

Cost estimates for decommissioning 

a large nuclear plant are $300 million 

or more, plus the cost of demolishing 

non-contaminated materials. The NRC 

decommissioning rules require companies to establish funds to pay for the 

future decommissioning of their plants.

Similar financial procedures are also 

required for other types of nuclear 

facilities, including plants that prepare 

fuel for nuclear power plants or process radioactive materials.

Some facilities that previously used 

nuclear materials in processing or 

manufacturing activities require special 

management attention. The NRC works 

to assure timely cleanup of certain 

unusual and difficult sites, particularly 

those with a lot of soil contamination or 

with old, contaminated buildings. The 

cleanup may take several years, but 

then the site can be used safely for 

any purpose.

NUREG/BR-0164, Rev. 9 

June 2012