Nuclear Power Info Tracker | Nuclear Reactor Definitions
Here is a list of common terms used in the Nuclear Power Information Tracker interactive map.
Boiling Water Reactor
A reactor in which the thermal energy produced by the nuclear fuel boils water inside a vessel to create steam. This steam spins a turbine generator to create electricity, and is then condensed back into water and returned to the vessel for reuse.
How does a boiling water reactor work? — Additional detailed information and diagrams outlining how this type of reactor works. Download the pdf
It may seem surprising that there are no West Coast reactors among the 27 found by the tracker's Earthquake Risk filter, but there is a reason for this. Decades ago, the U.S. government determined that the hazard posed by seismic activity – earthquakes – in the central and eastern parts of the country was greater than previously believed. Consequently, the NRC enacted regulations in 1996 that required new reactors built in these areas to be designed with protection against the greater hazard. But NRC did nothing about seismic protection at existing reactors operating in these areas for the next decade. In the summer of 2005, the NRC began examining the potential risk from reactors operating with less protection than necessary against the known seismic hazard. The NRC’s studies identified the 27 most vulnerable reactors based on current information. Thus far, the NRC has not required the known protection shortcomings to be resolved, even at the high risk reactors.
What is the spent fuel pool? — Additional detailed information and diagrams of the spent fuel pool and why this type of storage makes U.S. power plants vulnerable to attack. Go to web page | Download the pdf
Fire Protection Problems
Nuclear reactors that currently do not comply with either the fire protection regulations adopted by the NRC in 1980 or the alternate fire protection regulations adopted by the NRC in 2004. The owners of these reactors have notified the NRC of their intentions of acheiving compliance with the alternate regulations over the next few years or so.
For several years prior to the March 2011 tsunami that crippled the Fukushima nuclear plant in Japan, the NRC has known that 35 U.S. reactors faced flooding hazards potentially greater than they are designed to withstand. Nuclear plants are built next to rivers, lakes, and oceans because they require vast quantities of cooling water to carry away the large amounts of waste heat. (Today's nuclear plants produce two units of waste heat for every unit of electricity they generate.) Many nuclear plants along a river have one or more dams located up that river. If a dam failed, the ensuing flood waters could overwhelm the plant's protective barriers just the tsunami crashed over Fukushima's seawall. The NRC has plans to resolve this flooding hazard concern over the next few years. The plants might be okay as-is, or the plants may only be protected by luck - they are okay as long as the dam remains intact. The NRC won't know until it completes its homework. And Americans won't be protected until this safety question is finally answered.
Groundwater Leaks Reported
The nuclear power plant has reported a past spill, leak or other inadvertent release of radioactively contaminated water to the environment. This contaminated water could potentially make its way onto public lands and into drinking water supplies.
Heightened NRC Attention
Within the NRC's reactor oversight process, safety levels at all operating reactors are evaluated every three months using performance indicators for approximately two dozen key parameters coupled with findings from NRC's inspections. A reactor is flagged as "heightened NRC attention" if its safety levels drop below specified thresholds. For these reactors, the NRC responds with additional inspection efforts to ascertain the causes of their declines and verify that steps are being taken to correct the problems.
NRC Reactor Oversight Process— The Nuclear Regulatory Commission's report summary on nuclear power plant safety and performance. Go to NRC website
High Temperature Gas-Cooled Reactor
A reactor in which the thermal energy produced by the nuclear fuel heats a gas (usually helium). This hot gas flows through a heat exchanger surrounded by water; the heat boils the water to generate steam, which spins a turbine generator to create electricity. The steam is then condensed back into water and returned to the heat exchanger for reuse.
Inherently Safe Reactors
An inherently safe reactor, in theory, would be designed, operated, and monitored in such a way that the reactor would never be damaged and, as a result, no radioactivity would ever be released to the environment. No such reactor currently exists. The risk from existing reactors is so real and so large that liability insurance from private companies is financially impossible, thereby requiring federal liability protection.
Liquid Metal Fast Breeder Reactor
A reactor in which the thermal energy produced by the nuclear fuel heats liquid sodium. This hot liquid sodium enters a heat exchanger and transfers the heat to a second loop of liquid sodium. The sodium in this second loop then enters a heat exchanger surrounded by water; the heat boils the water to generate steam, which spins a turbine generator to create electricity. The steam is then condensed back into water and returned to the heat exchanger for reuse. This type of reactor is called a “breeder” reactor because it is designed to generate more fuel than it consumes, by converting certain unusable uranium atoms into usable plutonium atoms.
Near misses are events where combinations of broken or impaired safety equipment and/or poor worker performance spurred the Nuclear Regulatory Commission to send a special inspection team, augmented inspection team, or incident investigation team to the site. The NRC dispatches a special inspection team when conditions may increase the chance of reactor core damage by a factor of 10. An augmented inspection team is sent when the risk can be increased by a factor of 100. An incident investigation team is sent when the risk was increased by a factor of 1,000 or more.
The “Near Misses” filter on the Nuclear Power Information Tracker shows reactors that have recently experienced a near-miss event. This list is updated in our NRC and Nuclear Power Safety report, which appears early each year.
Pressurized Water Reactor
A reactor in which the thermal energy produced by the nuclear fuel heats water inside a vessel to over 500ºF, but high pressure within the vessel (nearly two thousand pounds per square inch) prevents the water from boiling. This hot water flows through a heat exchanger surrounded by water; the heat boils the water to generate steam, which spins a turbine generator to create electricity. The steam is then condensed back into water and returned to the heat exchanger for reuse, and the pressurized water is cooled down and returned to the reactor.
How does a pressurized water reactor work? — Additional detailed information and diagrams outlining how this type of reactor works. Download the PDF
PWR Containment Sump
A safety incident in which a hole opens in the metal pressure vessel or attached piping in a pressurized water reactor (PWR), causing the water to empty from the reactor and spill onto the floor of the containment building. The high-pressure water, as it escapes through the hole, scours thermal insulation and protective coatings (i.e., paint) off adjacent piping, equipment, and structures. This debris is carried to the floor of the containment building as well, where it can block the inflow of water into the sump, thereby preventing water from getting pumped back to the pressure vessel to cool the nuclear fuel.
Regulatory Malpractice: The NRC's Handling of the PWR Containment Sump Problem — This report exposes regulatory malpractice by the NRC regarding the pressurized water reactor (PWR) containment sump problem. This problem afflicts 68 of the 103 nuclear reactors operating in the United States and makes it much more likely that one of these reactors will experience the ultimate disaster: meltdown with containment failure. Download the report
Year Plus Outages
An outage at a nuclear power plant that lasts more than a year. The majority of such occurrences resulted from numerous violations of federal regulations that require plant owners to find and fix safety problems in a timely, effective manner, coupled with the NRC's inability to detect those violations (allowing problems to multiply and worsen as a result).
Walking a Nuclear Tightrope: Unlearned Lessons from Year-plus Reactor Outages — This report by the Union of Concerned Scientists identifies common themes among extended outages and steps the NRC must take to end these costly and avoidable threats to public health and the U.S. economy.
Go to web page | Download the report | Download the fact sheet