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Nuclear Plant Meltdown

Nuclear power plants are essentially fancy steam plants. They use radioactive materials that emit heat from nuclear fission. The heat turns water into steam, which powers generators that produce electricity.

How Nuclear Power Plants Work

When they fail, the primary cause is usually too much heat. Cooling systems lose power, are shut down improperly or have mechanical failures that lead to dangerous buildups of heat and pressure. The resulting explosions then spread radioactive material around, killing people and leaving spaces uninhabitable for potentially hundreds of years.

Nuclear Energy Explained: How does it work? 

Three of the best known nuclear reactor failures are Three Mile Island in the United States, Chernobyl in the former Soviet Union and Fukushima Daiichi in Japan. The following information on those three accidents is from the Union of Concerned Scientists.

Click Here for a direct link to their entire article: A Brief History of Nuclear Accidents Worldwide - Published Oct 1, 2013

Three Mile Island

Middletown, Pennsylvania, USA, March 28, 1978

The partial meltdown at Three Mile Island Unit 2 is considered the most serious nuclear accident in U.S. history, although it resulted in only small radioactive releases.

Three Mile Island Nuclear Power Plant - Photo take by an employee of the Environmental Protection Agency.
Three Mile Island Nuclear Power Plant - Photo take by an employee of the Environmental Protection Agency.

How did it happen?
The accident began with failures in the non-nuclear secondary system, followed by a human-operated relief valve in the primary system that stuck open, which allowed large amounts of nuclear reactor coolant to escape. Plant operators’ initial failure to correctly identify the problem compounded it. In particular, a hidden indicator light led to an operator manually overriding the automatic emergency cooling system because he mistakenly believed that too much coolant water in the reactor had caused the steam pressure release. Eventually the reactor was brought under control, although the full extent of the accident was not understood until later.


Chernobyl, Ukraine (former Soviet Union), April 26, 1986

Chernobyl is considered the world’s worst nuclear disaster to date. It occurred on April 26, 1986, when a sudden surge in power during a reactor systems test resulted in an explosion and fire that destroyed Unit 4. Massive amounts of radiation escaped and spread across the western Soviet Union and Europe. As a result of the disaster, approximately 220,000 people had to be relocated from their homes.

Chernobyl Nuclear Power Plant
Chernobyl Nuclear Plant after meltdown and encased in the protective sarcophagus. 

How did it happen?
Unit 4 was to be shut down for routine maintenance. A test was conducted to determine the plant equipment’s ability to provide sufficient electrical power to operate the reactor core cooling system and emergency equipment during the transition period between a loss of main station electrical power supply and the start-up of the emergency power supply. Workers did not implement adequate safety precautions or alert operators to the electrical test’s risks. This lack of awareness led the operators to engage in actions that diverged from safety procedures. Consequently, a sudden power surge resulted in explosions and nearly complete destruction of the reactor. The fires that broke out in the building contributed to the extensive radioactive releases.

Fukushima Daiichi

Fukushima, Japan, March 2011

The earthquake and tsunami that struck eastern Japan on March 11, 2011, caused a serious accident at the Fukushima Dai-ichi nuclear power plant on the northeastern coast of Japan.

Fukushima Daichi Nuclear Power Station. (Fukushima, Japan) - Photo Credit: Tokyo Electric Power Co., TEPCO
Fukushima Daichi Nuclear Power Station. (Fukushima, Japan) - Photo Credit: Tokyo Electric Power Co., TEPCO

How did it happen?
The earthquake cut off external power to the reactors. tsunami, which reached levels more than twice as high as the plant was designed to withstand, disabled backup diesel generators, crippling the reactor cooling systems. Battery power was quickly exhausted, and overheating fuel in the plant's operating reactor cores led to hydrogen explosions that severely damaged three of the reactor buildings. Fuel in three of the reactor cores melted, and radiation releases from the damaged reactors contaminated a wide area surrounding the plant and forced the evacuation of nearly half a million residents.

After reading about those catastrophic failures, you would think we want nuclear plants to be shut down. However, that's not the case at all.

First, nuclear plants provide the United States with about 20% of it's total power. It's simply not possible to shut them down because there isn't enough spare power available from all the other sources.

How Much Power Does A Nuclear Reactor Produce? Infographic provided by the United States Office of Nuclear Energy
How Much Power Does A Nuclear Reactor Produce? Infographic provided by the United States Office of Nuclear Energy

Second, the real risk of nuclear power is far less than existing power plants.

Fine particles from coal power plants kill an estimated 13,200 people each year in the US alone, according to the Boston-based Clean Air Task Force (The Toll from Coal, 2010). Fossil fuels kill far more people every year than all the nuclear power plant disasters in history combined.

Having said that, when a nuclear plant fails, you must know how to react. The first step is figuring out if you're at risk.

Locations of Nuclear Power Plants Worldwide

Wikipedia has a great reasource so you can find out if a Nuclear Power Plant is near you. If one is within 100 miles, you should make sure you're ready in the event of an emergency.

The table linked below lists all currently operational power stations with current net capacity over 1,000 MW. Some of these may have reactors under construction, but only current net capacity is listed. Capacity of permanently shut-down reactors is not included, but capacity of long-term shut-down reactors (today mainly in Japan) is included. Power stations with past net capacity over 1,000 MW and current net capacity under 1,000 MW are listed in third table.


You can also down the entire Wikipedia table as a PDF document by Clicking Here.

There are several national and international organizations that provide details on operating nuclear power plants. Links to all the major ones are below.

Click Here for the Nuclear Energy Institute Map of U.S. Nuclear Plants.

Click Here for the United States Nuclear Regulatory Commission Map of Power Reactor Sites.

Click Here for the International Atomic Energy Agency Power Reactor Information System (PRIS).

Click Here for the Carbon Brief Map of The World's Nuclear Power Plants.

Here's what happens during a nuclear plant meltdown.

Preparation - Survival

Emergency Classification

The Nuclear Regulatory Commission (NRC) has established Emergency Classifications that group events or conditions according to (1) potential or actual effects or consequences, and (2) resulting onsite and offsite response actions. The emergency classifications increase in severity from Notification of Unusual Event (NOUE); Alert; Site Area Emergency (SAE); and General Emergency (GE). Both nuclear power plants and research and test reactors use these terms as defined below.

The vast majority of events reported to the NRC are routine in nature and are handled outside of our incident response program.

  • Notification of Unusual Event (NOUE) – A situation is in progress or already completed which could potentially degrade the plant's level of safety or indicate a security threat to the facility. No releases of radioactive material requiring offsite actions are expected unless safety systems degrade further. [Note: The terms Notification of Unusual Event, NOUE and Unusual Event are used interchangeably.]

    Purpose: This classification ensures the first steps for future response are being carried out, that operations staff are at the ready, and that the plant systematically handles unusual event information and decision-making.

  • Alert – Events are in progress or have occurred which have (or could) substantially degrade the plant safety; or, a security event that could threaten site personnel or damage to site equipment is in progress. Any offsite releases of radioactive material that could occur are expected to be minimal and far below limits established by the Environmental Protection Agency's (EPA) protective action guides (PAGs).

    Purpose: This classification ensures that emergency personnel are ready and available to respond if the situation becomes more serious or to perform confirmatory radiation monitoring if required, and also ensures that offsite authorities receive current information on plant status.

  • Site Area Emergency (SAE) – Events are in progress or have occurred which have caused (or likely will cause) major failures of plant functions that protect the public, or involve security events with intentional damage or malicious acts that could lead to the likely failure of (or prevent effective access to) equipment needed to protect the public. Any offsite releases of radioactive material are expected to remain below EPA PAG exposure levels beyond the site boundary.

    Purpose: A SAE declaration ensures: a) emergency response centers are staffed; b) monitoring teams are dispatched; c) personnel required for evacuating nearby areas are at duty stations if the situation becomes more serious; d) proper consultation with offsite authorities; and e) government authorities are providing updates to the public.

  • General Emergency – Events are in progress or have occurred which: a) have caused (or shortly will cause) substantial reactor core damage, with the potential for uncontrolled releases of radioactive material; or, b) involve security events that deny plant staff physical control of the facility. Offsite releases can be reasonably expected to exceed EPA PAG exposure levels beyond the plant site.

    Purpose: A GE declaration initiates predetermined protective actions for the public including: a) continuous dose monitoring by the licensee and offsite organizations; b) additional protective measures as necessitated by potential or actual releases; c) consultation with offsite authorities; and, d) updates to the public by government authorities.

Nuclear materials and fuel cycle facility licensees have two emergency classifications:

  • Alert - Events may occur, are in progress, or have occurred that could lead to a release of radioactive material[s], but below the level requiring an offsite response to protect the public.

  • Site Area Emergency - Events may occur, are in progress, or have occurred that could lead to a significant release of radioactive material[s] requiring an offsite response to protect the public.

Click Here for information on what to do from the United States government website, Ready.gov.

Click Here to download a PDF file with information on what to do from the United States government website, Ready.gov.

PDF Information from Ready.gov

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This information is presented to make people aware of the larger world around them. If you can prepare for something as devastating as this, you're much more likely to be ready for smaller disruptions. Be aware and prepare.

Updated 4/15/2021
Updated 6/26/2021
Updated 3/3/2022