"A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter; a modern thermonuclear weapon weighing little more than a thousand kilograms can produce an explosion comparable to the detonation of more than a billion kilograms of conventional high explosive.
Thus, even single small nuclear devices no larger than traditional bombs can devastate an entire city by blast, fire and radiation. Nuclear weapons are considered weapons of mass destruction, and their use and control has been a major focus of international relations policy since their debut." [1]
A nuclear weapon can be described briefly like above. It seems to be like a toy, when a person tries to explain its functioning and affects. Issue of nuclear armament is not this much simple. Nuclear armament has a crucial affect on world politics and it will be one of the determinants in the future of human lives. International treaties which aim to control nuclear armament and nuclear proliferation treaties seem to protect world from radioactive massacres but this is no more than a sweet dream.
Two leading powers about nuclear weapons are USA and Russia. These two countries own nearly 90% of world's all nuclear weapons and their development of nuclear weapons will not be controlled. It is not clear that what those two countries developing underground. USA paranoia of Iran's nuclear power is derived from USA itself because USA does the same thing which USA blame Iran for.
US is insisting on the sanctions which will limit Iran's nuclear program, also US informally threatens Iran with a possible intervention which will be aiming at stopping the nuclear program of the Iran and punish Iran Government. This is a kind of US tradition over the countries which US sees as "threats"!!! On the other hand new nuclear fuel swap proposal which was signed by Turkey, Iran and Brazil, constructs a new alliance for nuclear power. Turkey and Brazil rejected the sanctions on Iran in the UN Security Council. Sides are getting sharper and nuclear power is becoming unstoppable. US is the most powerful country on the nuclear energy and nuclear weapons, if nuclear energy and nuclear weapons are so much dangerous and if they should be controlled, should not the sanctions applied to the US first?
Russia's concerns about the missile shield project which is planned to be constructed over Europe should be a signal for all the world that Russia is also developing nuclear weapons and Russia desires to use those weapons effectively when needed. Russia should prevent the nuclear missile shield project to achieve these aims. It is also known that Russia has an important nuclear heritage from the Soviet Union. Russia does not refrain from showing its nuclear power by selling nuclear technology or building nuclear power plants to other countries.
Russia will construct a nuclear power plant to Turkey and Russia also planning to sell nuclear weapons and nuclear missile infrastructure to Iran. All these events show that the sides are getting more clear. Russia will have the leading role in the Iran side and US is so much against Iran's nuclear program and US is aiding Israel for crushing Iran's nuclear plans. Israel's plans to sabotage Iran's nuclear program is also known. MOSSAD agents are assassinating officials and engineers of the Iran nuclear program.
Old rivals US and Russia are becoming hostile to each other day by day. Start 2 which was signed for nuclear weapons proliferation cannot stand valid for too much. Iran and Israel are both aggressive against each other and they may become tools for a 3 rd World War. In a situation which Iran and Israel gets into a conflict world powers will be divided into two and one of the main reasons and determinants of this conflict will be the nuclear power.
Uranium enrichment shown as a way to produce more energy and it is a need for industrial and energy development. Uranium enrichment is not only consists of this, if nuclear technology is developing, nuclear weapons are developing too. If uranium is enriched and it can produce more energy then a nuclear missile or you may call it a nuclear bomb will have more impact because of the enriched material used in it. If you think that nuclear energy will be important in the future and it will be used as a weapon in a war situation, huge massacres will be on the way. In this sense sanctions towards the nuclear programs are must but this sanctions issue is a tool for countries who have power to threaten other countries which desire to have power. So these sanctions are not result of a good will or in other words, US and UN are not insisting on these sanctions for protecting human lives. US wants to be the only power which can use nuclear weapons. It seems to be a quite simple and classical approach but that is the truth beyond nuclear power issue.
Today's technology gives the chance that people can use nuclear energy to develop and enrich world. Nuclear energy has a huge and long lasting power so growing world population will need it. If human kind chooses to enrich the uranium for not enriching world but killing people then there will not be a world to live in the future. Nuclear weapons' affect is not only a destruction affect radioactive remains of the nuclear missiles will simply destroy everything which humans live for.

[1]www.wikipedia.org