What are some difficulties scientists encounter in producing controlled nuclear fusion reactions?

Answer 1

To make fusion a source of energy we would need to be able to get hydrogen to start moving extreamly fast and that would take heating it up to 1,000,000 degrees and we cannot do that How to sustain the reaction for an indefinite period of time. We are currently able to hold a fusion reaction for just a few nanoseconds,

Answer 2

In the sun, fusion is self sustaining at quite a low rate per unit volume (about 0.3 watt/m3) and at temperatures of around 10 million degC, but here the density of the hydrogen material is very high due to the great gravitational forces.

The rate of nuclear fusion depends strongly on density and temperature, so the fusion rate in the core is in a self-correcting equilibrium: a slightly higher rate of fusion would cause the core to heat up more and expand slightly against the weight of the outer layers, reducing the fusion rate and correcting the perturbation; and a slightly lower rate would cause the core to cool and shrink slightly, increasing the fusion rate and again reverting it to its present level.

On earth it is impracticable to have a reactor working at such conditions, and it would have to be huge in dimensions anyway. A man made fusion reactor has to achieve much higher temperatures, hundreds of millions degC, to achieve fusion at conditions that can be produced in a feasible reactor, and the hot gas has to be contained by magnetic means to get the sort of plasma required in a stable configuration. This is the basis of the tokamak type of reactor which has been built in increasing sizes, the next step is ITER. So far fusion has only been achieved for fractions of a second, and the power input has been much greater than the output. If ITER is successful the boundaries will be pushed out further, but it will be 10 years before this is achieved. These are large expensive multinational projects and there seems no quick easy route to success. A further problem is how to extract the energy produced from fusion in such a machine, and that is not obvious in engineering terms.

Another approach which is currently getting a lot of publicity is the laser method being developed by the NIF (National Ignition Facility). This may be successful in achieving fusion in a small pellet of fuel, but again one wonders how it is proposed to engineer a practical power plant from such a set up.

Answer 3

The short representation of the answer is: "It is hard to hold something when it is heated to a million degrees and anything that might hold it vaporizes."

Fusion is the combination of two atoms into a single, larger atom. Energy is generated if the atoms are small. Fusing large atoms uses more energy than it produces.

Looking at the problem very simplistically, the problem with fusion is that it requires a lot of power to get the reaction going. If there is not enough power produced by the reaction to keep it going, or fuel is not available for the reaction to continue, then the reaction stops. The power needed to start a fusion reaction is immense, and well above the melting and boiling points of any object that might contain the reaction. So, the reaction must be contained by a force field, or something like it. This also uses a lot of power, and leaves us with the problem of how to feed fuel into the reaction through the force field.

Attempts to do all this have been, and continue to be, made. Large amounts of energy are produced in some of these attempts, but not enough to keep the reaction going. (And believe me, when someone is able to keep a reaction going, you will hear about it.)

One alternative to this is what is called "cold fusion." Here, people try to cause atoms to fuse by means other than the application of lots of power. Various organizations have put a lot of money into this, and some continue to do so, but there is not much more hope of achieving success now than there there ever was in the past. Most experts call it a lost cause.

Answer 4

The temperature and pressure required to initiate it as well as confinement problems and instabilities. After that is the fact that even the best attempts so far can't even make "breakeven" even when they do work.

Answer 5

It's not so difficult to make a simple assembly. The first pile made was literally a pile of graphite blocks with fuel of natural uranium metal in a regular lattice arrangement. The graphite needs to be of high purity.

The difficulty comes in making it safe in a useful form, either for power production or for for producing medical or industrial isotopes. The operators must be well shielded, and in the case of a high pressure power producing reactor the pressure circuit must be built to the highest engineering standards. Then there must be all sorts of safety features both active and passive.

Nuclear reactors are inherently dangerous because of the radiation and the active fission products formed in the fuel, the main difficulty is in achieving a safe design which can be relied on to a very high standard.

Answer 6

There are two main problems to overcome before fusion can produce energy:1) it must be able to achieve high enough temperatures to start the reaction.

2) Must contain plasma.

Answer 7

The major problem with using nuclear fusion is that at the moment we cannot get to a high enough temperature needed to overcome the repelling nature of the positively charged nuclei.

Answer 8

Extreme heat and extreme pressure.

Answer 9

• confinement
• breakeven