Nuclear and Conventional Weapons
Weapon is used to mean an explosive weapon, such as a bomb, the warhead of a missile or an artillery shell. All such weapons contain explosive material which explodes when suitably triggered. In conventional weapons, the explosive material is something that can undergo some chemical reaction which proceeds extremely quickly and releases a lot of energy. Basically it can ‘burn’ so fast that it explodes. The first explosive material used in weapons was gunpowder, nowadays more powerful explosives like TNT and RDX are used.
The explosive material in a nuclear weapon can undergo a nuclear reaction at an incredibly fast rate. What a nuclear reaction is and why it releases so much energy is explained later.
A nuclear weapon is an explosive device that derives its destructive force from nuclear rather than chemical reactions. A nuclear reaction releases about a million times more energy than does
One measure of the power of a weapon is given by the total amount of energy released in the explosion. This is called the yield of the weapon. The yield of nuclear weapons is usually expressed in terms of the equivalent amount of TNT which would release the same amount of energy. So a single ‘small’ nuclear weapon whose yield is ten kilotons (10,000 tons of TNT) releases the same amount of energy as ten kilotons, i.e. 10,000 kilograms of TNT.
To get a better idea of what these numbers mean, let us see how many conventional bombs would release the same amount of energy as one such small nuclear bomb. A nuclear bomb with a 10 kiloton yield weighs about 500 kg whereas a conventional bomb of the same weight contains about 250 kg of explosives. So a single small nuclear bomb releases as much energy as about 40,000 conventional bombs. The explosion of such a bomb is then like forty thousand conventional bombs exploding simultaneously at the same point.
Nuclear weapons are tremendously more powerful than conventional ones. They cause death and destruction on a much larger scale. They are indeed weapons of mass destruction.
The second major difference is that a nuclear explosion produces large amounts of “radioactive” material that give out deadly rays of nuclear radiation. (This is also called the fallout.) A large dose of radiation can kill a human instantly. Exposure to a somewhat smaller amount can have even worse consequences. It can cause severe illness leading to slow death after days or even years of suffering. Radiation can cause genetic damage leading to babies being born deformed. It contaminates large areas of land, making it useless for agriculture for years or even decades.
These aspects of nuclear weapons thus introduce a new dimension of horror. The poisoning of humans and their environment by radiation makes the process of recovering from a nuclear attack a long and painful one.These are the reasons why a large section of informed and sensible people in the world consider nuclear weapons to be unacceptable, much more so than biological and chemical weapons, which are already banned by international agreement.
Two types of nuclear reactions are used in nuclear weapons. The nuclei of some heavy elements like uranium or plutonium can split into two roughly equal sized nuclei with the release of energy. Such a process is known as nuclear fission. On the other hand, two light nuclei can undergo nuclear fusion to combine and form a single nucleus, again with the release of energy. These reactions are explained in detail later in the section on the Physics of a nuclear reaction. All nuclear weapons use fission and fusion reactions in different combinations. From the point of view of military usage, these weapons historically fall into two classes.
The first class contains tactical, or non-strategic weapons. Early generations of tactical weapons were typically low-yield weapons (having yields ranging from less than 1 kiloton to 10-15 kilotons) that were designed to be used in the battlefield against military formations. Russia apparently still retains many of these battlefield weapons, but most U.S. tactical weapons of this sort have been retired and dismantled. Modern U.S. non-strategic weapons can have a variable yield design, which allows their explosive power to be set from 0.3 kilotons to well over 100 kilotons (thus it is often impossible to assign a classification based only upon the explosive power of the weapon).
The second class contains strategic nuclear weapons (with yields of 100 kilotons or greater), which are high-yield weapons designed to produce enormous blast damage and also to kill civilian populations in cities. The different types of nuclear weapons that have been built or thought of are described below.
Pure Fission Weapons
Weapons in which only the fission reaction takes place are called pure fission weapons or simply fission weapons. Such were the bombs dropped on Hiroshima and Nagasaki. These are the simplest nuclear weapons to design and build. They form the basis for developing other types of weapons. Their yield can range from a few tons to about a few hundred kilotons. They can be both tactical and strategic weapons. The largest pure fission weapon tested is believed to be a 500 kiloton bomb called Mk-18 which was tested by the USA on November 15, 1952.
Boosted Fission Weapons
The efficiency of a fission weapon can be dramatically increased by introducing a small amount of material that can undergo fusion. Such weapons are called boosted fission weapons. In boosted weapons, the fission reaction takes place first and produces the required temperatures and densities for the fusion reaction. The fusion in turn accelerates the fission reaction. The fusion only serves to help the fission process go faster and makes the weapon more ‘efficient’. It contributes to only about 1% of the yield. Since boosted fission weapons are more efficient than pure fission weapons, they can be made lighter for the same yield. So most of the strategic fission weapons deployed today are boosted fission weapons.
Thermonuclear weapons, also called hydrogen bombs, get most of their yield from the fusion reaction. As in the case of boosted fission weapons, they require a fission explosion (called the primary stage) to trigger the fusion (the secondary stage). However, unlike the boosted weapons, thermonuclear weapons contain a substantial amount of fusion fuel and most of their yield comes from fusion. These are the most powerful nuclear weapons, sometimes with yields of more than a megaton (a megaton equals a million tons; in nuclear weapons, a megaton equals a million tons of TNT explosive power). A third fission stage can also be added to produce very high yield weapons of tens or even a hundred megatons.
The most powerful nuclear weapon to have been tested so far is the Tsar Bomba, a 50 megaton three-stage weapon exploded by the USSR on October 30, 1961. However it is not necessary for a thermonuclear weapon to have such high yields. The B61 (Mk-61) class of tactical thermonuclear weapons deployed by the USA have yields which can be adjusted to be as small as 0.3 kilotons (300 tons).
Enhanced Radiation Weapons
Enhanced radiation weapons, also called neutron bombs, are small thermonuclear weapons which are designed to produce intense nuclear radiation. These are tactical weapons designed to kill soldiers protected by armor (for example, inside tanks). The radiation produced by the neutron bombs can easily penetrate the armor of tanks and kill the humans inside.
Salted Nuclear Weapons
Salted nuclear weapons, or cobalt bombs, are thermonuclear weapons which are designed to produce a large amount of long lasting radioactive fallout. This would result in large scale radioactive contamination of the area they are dropped in. The fallout from salted weapons is much more intense and lasts much longer than from unsalted weapons. The long term effects of such weapons would therefore be much worse. These weapons are called ‘Doomsday Devices’ since they could possibly kill everyone on earth. Fortunately, though these weapons have been conceived of and discussed, none have been built or tested (as far as we know).
Pure Fusion Weapons
These are fusion weapons that would not need a fission trigger for the thermonuclear explosion. Active research is going on in the US to develop these weapons, but with no success so far. Since there is no fission trigger, pure fusion weapons could be made with very low yields. Yet, the lethality of these weapons due to nuclear radiation and explosive force would still be great. For instance, a pure fusion weapon with an explosive force equivalent to one ton of TNT would kill people in an area nearly a hundred times larger than a conventional bomb with the same explosive force.
Another feature of these weapons is that since they do not use fissile material, their development would not be restricted by the Fissile Material Cut-off Treaty or FMCT.
Given the devastation that can be caused by nuclear weapons, it is clearly very important that great precaution be taken to prevent their unauthorized use. PAL, which stands for permissive action links, are systems that make it impossible to detonate the weapon without proper authorization. These are electronic devices that prevent the activation or arming of the weapon unless the correct codes are inserted into it. Typically two codes should be inserted, simultaneously or close together. The codes are usually changed regularly.
Apart from preventing unauthorized use, it is equally important to ensure that the weapons do not explode accidentally. For example, if it is accidentally dropped during transportation (such incidents have occurred), it should not explode. A nuclear weapon is one-point safe if, when the High Explosive inside the weapon is initiated and detonated at any single point, the probability of producing a nuclear yield exceeding 4 pounds TNT equivalent is less than 1 in one million.
Nuclear reactors harness the energy produced in nuclear reactions to generate electrical power.
As an analogy, in a car engine gasoline is burned in a controlled way inside the cylinder to drive the motor. On the other hand if a lighted matchstick is dropped into the fuel tank the same gasoline will burn in a completely uncontrolled way and could lead to an explosion. As can be visualized from the analogy, a nuclear reactor is a complex mechanism compared to a bomb.
Although nuclear reactions take place in a reactor just as they do in weapons, the crucial difference is that the rate of the nuclear reaction is controlled in a reactor whereas in a weapon, once triggered, the reaction proceeds in an uncontrolled way leading to the explosion.
It is important to note that nuclear reactors were designed to produce plutonium – and not electrical power – in order to create the fissile material necessary to produce nuclear weapons. Plutonium does not exist in nature (in any more than microscopic quantities near large uranium deposits) and thus must be manufactured in the fuel rods of nuclear power plants. Nuclear reactors remain the only pathway to produce the plutonium required to make plutonium pits used in virtually all strategic nuclear weapons.
Plutonium is extracted from spent fuel rods (rods which have had most of their fissionable uranium consumed by nuclear reactions) by immersing the rods in highly acidic solutions and chemically separating the plutonium from the other dangerously radioactive elements in the rod (this must be done by remote control because of the intense radiation). Huge amounts of highly radioactive waste are thus produced, and in the U.S., millions of gallons of this waste remain in underground storage tanks, some of which are known to be leaking.
Nuclear reactors thus play a central role in creating fissile material for use in nuclear weapons. Any nuclear weapon which contains plutonium had its beginnings inside a nuclear reactor. Any nation which has a commercial size nuclear reactor will produce enough plutonium to make dozens of Hiroshima-size bombs per year.