Editing Nuclear fallout (section)

==Nuclear reactor accident==
{{See also|Comparison of Chernobyl and other radioactivity releases}}
Fallout can also refer to [[nuclear accident]]s, although a [[nuclear reactor]] does not explode like a nuclear weapon. The [[isotopic signature]] of bomb fallout is very different from the fallout from a serious power reactor accident (such as [[Chernobyl disaster|Chernobyl]] or [[Fukushima nuclear disaster|Fukushima]]).

The key differences are in [[volatility (chemistry)|volatility]] and [[half-life]].

===Volatility===
The [[boiling point]] of an [[chemical element|element]] (or its [[chemical compound|compound]]s) determines the percentage of that element that a power reactor accident releases. The ability of an element to form a solid determines the rate it is deposited on the ground after having been injected into the atmosphere by a nuclear detonation or accident.

===Half-life===
A [[half life]] is the time it takes the radiation emitted by a specific substance to decay to half the initial value. A large amount of short-lived isotopes such as <sup>97</sup>Zr are present in bomb fallout. This isotope and other short-lived isotopes are constantly generated in a power reactor, but because the [[critical mass|criticality]] occurs over a long length of time, the majority of these short lived isotopes decay before they can be released.

===Preventive measures===
Nuclear fallout can occur due to a number of different sources. One of the most common potential sources of nuclear fallout is that of [[nuclear reactors]]. Because of this, steps must be taken to ensure the risk of nuclear fallout at nuclear reactors is controlled. 
In the 1950s and 60's, the [[United States Atomic Energy Commission]] (AEC) began developing safety regulations against nuclear fallout for civilian nuclear reactors. Because the effects of nuclear fallout are more widespread and longer lasting than other forms of energy production accidents, the AEC desired a more proactive response towards potential accidents than ever before.<ref name="Uncertainty 846–884">{{cite journal |last1=Wellock |first1=Thomas |title=Engineering Uncertainty and Bureaucratic Crisis at the Atomic Energy Commission |journal=Technology and Culture |date=October 2012 |volume=53 |issue=4 |pages=846–884|doi=10.1353/tech.2012.0144 |s2cid=143252147 }}</ref> One step to prevent nuclear reactor accidents was the [[Price-Anderson Act]]. Passed by Congress in 1957, the Price-Anderson Act ensured government assistance above the $60 million covered by private insurance companies in the case of a nuclear reactor accident. The main goal of the Price-Anderson Act was to protect the multi-billion-dollar companies overseeing the production of nuclear reactors. Without this protection, the nuclear reactor industry could potentially come to a halt, and the protective measures against nuclear fallout would be reduced.<ref name="Probabilistic 920–941">{{cite journal |last1=Carlisle |first1=Rodney |title=Probabilistic Risk Assessment in Nuclear Reactors: Engineering Success, Public Relation Failure |journal=Technology and Culture |date=October 1997 |volume=38 |issue=4 |pages=920–941|doi=10.2307/3106954 |jstor=3106954 |s2cid=112329893 }}</ref> However, because of the limited experience in nuclear reactor technology, engineers had a difficult time calculating the potential risk of released radiation.<ref name="Probabilistic 920–941"/> Engineers were forced to imagine every unlikely accident, and the potential fallout associated with each accident. The AEC's regulations against potential nuclear reactor fallout were centered on the ability of the power plant to the Maximum Credible Accident (MCA). The MCA involved a "large release of radioactive isotopes after a substantial meltdown of the reactor fuel when the reactor coolant system failed through a Loss-of-Coolant Accident".<ref name="Uncertainty 846–884"/> The prevention of the MCA enabled a number of new nuclear fallout preventive measures. Static safety systems, or systems without power sources or user input, were enabled to prevent potential human error. Containment buildings, for example, were reliably effective at containing a release of radiation and did not need to be powered or turned on to operate. Active protective systems, although far less dependable, can do many things that static systems cannot. For example, a system to replace the escaping steam of a cooling system with cooling water could prevent reactor fuel from melting. However, this system would need a sensor to detect the presence of releasing steam. Sensors can fail, and the results of a lack of preventive measures would result in a local nuclear fallout. The AEC had to choose, then, between active and static systems to protect the public from nuclear fallout. With a lack of set standards and probabilistic calculations, the AEC and the industry became divided on the best safety precautions to use. 
This division gave rise to the [[Nuclear Regulatory Commission]] (NRC). The NRC was committed to 'regulations through research', which gave the regulatory committee a knowledge bank of research on which to draw their regulations. Much of the research done by the NRC sought to move safety systems from a deterministic viewpoint into a new probabilistic approach. The deterministic approach sought to foresee all problems before they arose. The probabilistic approach uses a more mathematical approach to weigh the risks of potential radiation leaks. Much of the probabilistic safety approach can be drawn from the [[radiative transfer]] theory in [[Physics]], which describes how radiation travels in free space and through barriers.<ref>{{cite journal |last1=Shore |first1=Steven |title=Blue Sky and Hot Piles: The Evolution of Radiative Transfer Theory from Atmospheres to Nuclear Reactors |journal=Historia Mathematica |date=2002 |volume=29 |issue=4 |pages=463–489 |doi=10.1006/hmat.2002.2360|doi-access=free }}</ref> Today, the NRC is still the leading regulatory committee on nuclear reactor power plants.