|Fig. 1: Graphic depicting the power plant (right).  (Source: F. Voris)|
When the general public perceives nuclear energy their minds immediately wander to the Trinity nuclear test, the Cold War, and massive amounts of destruction. The images of blinding flashes and mushroom clouds that are forever attached to nuclear energy bring with it a stigma that this technology is strikingly dangerous and has an infinite capacity for destruction.
In some cases, this is true. Nuclear energy was first harnessed in the form of a bomb during the Manhattan Project. It was developed with the express intention of creating a weapon so powerful as to destroy anything in its path, including the empires of Germany and Japan. After the successful use of nuclear weapons at the end of World War II, a global arms race ensued eventually leading to stockpiles of bombs capable of destroying humanity. With it came implications for the reputation of nuclear energy, and these repercussions now prevent humanity from utilizing nuclear energy for the low carbon-footprint energy source that it provides.
The Manhattan project took 4 years and $2.2 billion from 1942 to 1946 ($33 billion in 2017 dollars.)  This money was spent developing the most advanced and destructive technological achievement that humanity has ever seen. The significant investment required shows the precision needed in order to turn a slab of Uranium into a weapon of war. By developing an understanding of what it takes to make a nuclear bomb, and how it differs from a typical nuclear reactor in a power plant, this paper will address misconceptions about the dangers of nuclear power. By establishing this, it is hoped that public perception of nuclear power generation will improve by distancing perceptions of nuclear weapons from those of nuclear power generation.
In order to understand why nuclear power plants cannot behave like weapons, one must understand how their constructions fundamentally differ. For the purpose of this paper, the construction will be analyzed with regard to a fission bomb using at least 80% enriched U-235.  The weapons grade U-235 atoms split when struck by a neutron. Once this occurs, energy, various byproducts, and most importantly two more neutrons are released.  These two neutrons could then in theory strike two more U-235 atoms releasing four more neutrons. These four neutrons could then strike four atoms, in turn, release eight neutrons. This reaction is said to be supercritical, meaning that fission is happening at an increasing rate. (See Fig. 1.)
Nuclear bombs are designed to maximize efficiency and minimize the duration of the energy release. In order to do so, the Uranium core of the bomb is shielded in a tamper (a material that reflects neutrons.) The tamper creates a much more intense reaction because it ensures the neutrons are remain within the core of fissile material for longer. This increases the probability that one of these neutrons will strike and split another U-235 atom.  The reflection of these neutrons increases the efficiency of the bomb allowing for the release of more energy.
While it is true that both devices rely on chain reactions, the reactions in a power plant were designed in order to make the massive and immediate release of energy seen in the bomb very unlikely. First, instead of the U-235 concentrations of greater than 80% found in weapons, nuclear power plants usually contain 3-5% U-235. [2,4] These far lower percentages mean that the reactor cannot go supercritical without a moderator to slow neutrons and increase the probability of another U-235 fission.  In the case of a light water reactor, water acts as this moderator. In the event of a disaster such as the reactor failure at the Idaho National Laboratory, it is possible for the fuel to lose contact with the moderator stopping the supercritical reaction.  Since the reactor was not designed like a bomb, this is one of many design weak points that would stop the chain reaction from behaving like one in a weapon.
Lastly, while nuclear bombs are tampered in order to accelerate the fission reaction, fuel rods are designed with control rods to moderate it. Nuclear power plants insert control rods between the U-235 nuclear fuel rods. These control rods are made out of a material like Boron that absorbs the neutrons that have been released, preventing an increasing rate of fission from occurring. 
While every aspect of the design of a nuclear power plant lowers the probability that the reaction becomes supercritical, it has happened in the past. When this is the case, the main concern is radiation. Explosions can and have happened, but they have been nowhere near the same scale and destruction of a nuclear weapon. A nuclear reactor exploding to this degree would be extremely rare, if not impossible.
This is not to say that nuclear power plants come without dangers. The meltdown described above would release terrible amounts of radiation, as in the case of Chernobyl, or even threaten life in the case of a supercritical reactor at the Idaho National Labratory. With that being said, neither of these instances resemble the scale and destruction associated with the public's perception of a nuclear explosion. Nuclear energy has proven to be a means of energy production with a very low carbon footprint. When we shape our discussions about whether to implement the technology, it is essential to consider the true dangers of nuclear energy generation rather than those induced by negative stigmas about nuclear weapons.
© Frank Voris. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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