The heavy method is to enrich natural uranium

The nuclear test of the Korea of the North announces a progressive trivialization of this still elitist weapons The experts themselves were difficult to exclude that a terrorist group can control fire nuclear. However, physicists continue to think that the users club has little chance to grow up, or even should be reduced (see box). The building of a major weapons such as the Russia or a moderately powerful strike like that of the France force in effect requires a scientific and technological effort enormous. Régis Baudrillard, Director of materials at the Atomic Energy Commission, requires at least a few thousand researchers for more than a decade to achieve. A less wealthy State take longer still, with a battalion of hundreds of scientists only.

To make a nuclear warhead, need ingredients of course, the recipe, the Cook, but also a kitchen and a battery provided utensils. Several countries such as Pakistan or the Iran showed that it is possible today to get the recipe for a big cheque some valued at 10 million euros. On the other hand, ingredients and a well equipped kitchen are more difficult to obtain.

The raw material for a bomb, it is uranium-235 or plutonium-239. These radioactive materials must reproduce on a military head of civilian reactors, but exponentially fission chain reaction. The choice of one of the two ingredients depends on the means of production of the country. The heavy method is to enrich natural uranium. The mine contains mainly uranium 238 and only 1 of uranium 235. It is the latter which allows to set a sufficiently powerful fission, but if the focus up to 90. Experts believe that the 50 advanced by the IAEA (International Atomic Energy Agency) is insufficient. Enrichment requires a farm complex and costly centrifuge. All the more requires about 20 kilograms of uranium by head against 5 kilograms for plutonium.

Very sharp chemists

Most of the nuclear countries, like the North Korea, chose the path of the plutonium which means to have a nuclear power plant. The 238 natural uranium undergoes fission reactor that produces an average of 1 gram of plutonium per megawatt per day. From the IAEA, Koreans have therefore 20 kilograms. Their 5-megawatt reactor worked from 1987 to 1991. If it does not a large Central Park, it is therefore a matter of patience. Régis Baudrillard recalls that it then dispose of chemists very sharp to design the plant for the reprocessing of plutonium which must be extracted from the fission by-products.

The recipe is not done so. Because uranium or plutonium committed a fission that under the onslaught of an initial flux of neutrons and under specific conditions of temperature and pressure. Modern A bomb using chemical explosives to cause a violent implosion of fuel. This technology is difficult to master because the implosion must not leave too soon before have resulted in the fission of a critical mass of material. Researchers also use explosives to increase the density of the fuel, a trick which allows to reduce the critical mass of plutonium, and thus to a head with less material.

All these demands complicate the design of the heart of the bomb. It must be that each fission reaction, a sufficient number of neutrons go hitting fuel atoms for the string. The Korea of the North has shown by his essay succeeded in over twenty years to cross all of these steps. However, his enemies do not know if it will succeed the other three prerequisites for the formation of a powerful arsenal. All estimates, the seismic wave recorded this weekend indicate a power of explosion of a few kilotons. It is the most powerful Western heads "weigh" a few hundred kilotons each.

Understand the fission

The first challenge is whether properly instrument the atomic tests. Régis Baudrillard explains that the collection of data is essential to understand the operation of a head and to be able to reproduce it in large numbers with reliability. However such measures require very high-level technologies. It is also integrating heads to carry missiles, which is far from trivial. To properly its dramatic besogne, a missile ballistic or strategic must raise his head at the proper altitude and eject precisely its some warheads.

But the end of the end, what distinguishes the first nuclear class (USA, Russia, France, Britain and China) of other small players (India, Pakistan, Korea North and informally Israel), is the master of the H bomb. Because the bomb remains unstable and the design of reliable powerful loads is difficult.

This is why the galonnés nuclear physicists have adopted head to inertial confinement fusion. It is to cause the fusion reaction of isotope of hydrogen that produces more energy than fission. It imposes pressures however and initial temperatures very superior. Therefore, the H bomb is lit by a bomb. This technology therefore requires understanding the physics of fission but more that of the merger. Even the most competent teams recognize having much to advance the understanding of the phenomenon as shown in the expensive French fusion simulation program.