Design Basis Accident
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A design-basis event (DBE) is a postulated event used to establish the acceptable performance requirements of the structures, systems, and components, such that a
nuclear power plant A nuclear power plant (NPP), also known as a nuclear power station (NPS), nuclear generating station (NGS) or atomic power station (APS) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power st ...
can withstand the event and not endanger the health or safety of the plant operators or the wider public. Similar terms are design-basis accident (DBA) and maximum credible accident. Subtypes of DBEs are: * design-basis criticality: "A criticality accident that is the most severe design-basis accident of that type applicable to the area under consideration." * design-basis
earthquake An earthquakealso called a quake, tremor, or tembloris the shaking of the Earth's surface resulting from a sudden release of energy in the lithosphere that creates seismic waves. Earthquakes can range in intensity, from those so weak they ...
(DBE): "That earthquake for which the safety systems are designed to remain functional both during and after the event, thus assuring the ability to shut down and maintain a safe configuration." * design-basis
explosion An explosion is a rapid expansion in volume of a given amount of matter associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Explosions may also be generated ...
: "An explosion that is the most severe design-basis accident of that type applicable to the area under consideration." * design-basis
fire Fire is the rapid oxidation of a fuel in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Flames, the most visible portion of the fire, are produced in the combustion re ...
: "A fire that is the most severe design-basis accident of this type. In postulating such a fire, failure of automatic and manual fire-suppression provisions shall be assumed except for those safety class items or systems that are specifically designed to remain available (structurally or functionally) through the event." * design-basis
flood A flood is an overflow of water (list of non-water floods, or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are of significant con ...
: "A flood that is the most severe design-basis accident of that type applicable to the area under consideration." * design-basis
tornado A tornado is a violently rotating column of air that is in contact with the surface of Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the ...
(DBT): "A tornado that is the most severe design-basis accident of that type applicable to the area under consideration." Circumstances like the
2011 Tōhoku earthquake and tsunami On 11 March 2011, at 14:46:24 Japan Standard Time, JST (05:46:24 UTC), a  9.0–9.1 Submarine earthquake, undersea megathrust earthquake occurred in the Pacific Ocean, east of the Oshika Peninsula of the Tōhoku region. It lasted approx ...
were not considered within the design basis of the plant, and so the resulting
Fukushima I nuclear accidents The Fukushima nuclear accident was a major nuclear accident at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan, which began on 11 March 2011. The cause of the accident was the 2011 Tōhoku earthquake and tsunami, which ...
were described using this terminology as "beyond design basis" or "non-design-basis". However, some have claimed that the design basis for tsunami events at Fukushima was incorrect. Accidents caused by poor design, failure to follow listed safety procedures, or other forms of
human error Human error is an action that has been done but that was "not intended by the actor; not desired by a set of rules or an external observer; or that led the task or system outside its acceptable limits".Senders, J.W. and Moray, N.P. (1991) Human Er ...
are not considered to be beyond-design-basis accidents. The terminology can be unclear, however, because a poorly handled design-basis accident can result in conditions beyond what was considered likely, causing a beyond-design-basis accident. For this reason, some industry experts have criticized the use of design-basis terminology. The
Three Mile Island accident The Three Mile Island accident was a partial nuclear meltdown of the Unit 2 reactor (TMI-2) of the Three Mile Island Nuclear Generating Station, located on the Susquehanna River in Londonderry Township, Dauphin County, Pennsylvania, Londonderry T ...
and the
Chernobyl disaster On 26 April 1986, the no. 4 reactor of the Chernobyl Nuclear Power Plant, located near Pripyat, Ukrainian Soviet Socialist Republic, Ukrainian SSR, Soviet Union (now Ukraine), exploded. With dozens of direct casualties, it is one of only ...
are examples of design-basis accidents becoming non-design-basis accidents because of design deficiencies, inadequate training, procedures inadequate for the conditions (TMI), failure to follow operating procedures (Chernobyl), and control room design shortfalls.


Beyond-design-basis events

Beyond-design-basis events can reduce or eliminate the margin of safety of the structures, systems and components, possibly resulting in a catastrophic failure. The
Fukushima Daiichi nuclear disaster The Fukushima nuclear accident was a major nuclear accident at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima, Japan, which began on 11 March 2011. The cause of the accident was the 2011 Tōhoku earthquake and tsunami, which r ...
was caused by a "beyond-design-basis event": the tsunami and associated earthquakes were more powerful than the plant was designed to accommodate. The plant withstood the earthquake but the tsunami overflowed the seawall. Since then, the possibility of unforeseen beyond design basis events has been a major concern for plant operators.


See also

*
Lists of nuclear disasters and radioactive incidents These are lists of nuclear disasters and radioactive incidents. Main lists * List of nuclear and radiation accidents and incidents * List of nuclear and radiation accidents by death toll * List of civilian nuclear accidents * List o ...


References

{{Authority control * Nuclear accidents and incidents Nuclear reactor safety