beet1e: Miko - no, no leg pulling. Years ago when we started having problems with Saddam, there was analysis about nuclear fuels - for reactors and for weapons.
OK then, sorry for misunderstanding.
A nuclear weapon needs concentrated fuel because the considerations of size and total weight are crucial, whatever the cost.
It seems at first glance that a nuclear bomb core using 3% pure fuel would just have to be 23 times bigger than the one 70% using pure fuel to achieve the same power - bad enough where size and weight matters.
Not true - a concentration is impotrant to achieve critical mass and 3% bomb would need to be not 23 but probably 100 times more massive just to explode.
In reality, the yield of such bomb would be much, much less than of a 70% bomb 100 times smaller. The charge would not be heavier but also bigger in size/diameter. Since chain reaction starts at the center and only works for fractions of a millisecond before the mass is blown appart, less of the usefull mass of a 3% will have time to react.
A nuclear bomb's efficiency is very low - probably less then one percent of matter reacts under best circumstances, and the way to increase it is to have pure fuel and contain it together at critical mass as long as possible (against the force of a nuclear explosion pushing it apart!) which is much easier to do with smaller size core.
At the same time the power station is not being blown apart (God willing) and the 3% fuel has time to react more completely over time.
Yes, the fuel rods of 3% would have to be 23 times bigger that 70% rods, but:
1) Size is not important in a stationary reactor not intended for shooting out of a cannon
2) Cost of 70% rods would be thousands or millions of times higher than cost of 3% rods, not 23 times, Every schoolchild knows how to make a nuclear bomb. The purification is the biggest technological and financial challenge here and the goal of power station is to make money, not burn it.
3) 70% rods would be much more difficult to control to keep the reaction to a manageable sub-critical pace. If the safety system fails totally, the only reason you do not get full nuclear explosion (chain reaction with efficiency >1) is due to low-concentrated fuel.
If they ever reuse uranium from bombs for power stations, they will certainly dilute it to 3%, foregoing billions in purification expences.
4) 3% rods actually convert some of the 97% of "useless" uranium into plutonium and otehr stuff which can also be used for nuclear fuel. That is a principle of a breeder reactor - it produces more fuel than it consumes.
crowbaby: As an energy producing policy, it's utterly uneconomic.
That may be - but it does not seem so at a first glance. Politicians usually force businesses to waste money, not save it. Why would anyone want to build such a station if he could not turn profit?
There are many consideratins - that could be converted to money, for and against nuclear power. Once you add the cost of dealing with spent fuel, it becomes less attractive. On the other hand, if you quantify the risks of foreign oil supply or even massive domestic coal transportation being disrupted, the nuclear station will run for years on the fuel already present on premises.
We also have to remember that nuclear reactors used today are analogs of first steam engines - that used 1% of coal productively and covered whole countrysides black with soot. There is undoubtedly a lot of progress to be made that would make nukes smaller, safer and cheaper.
Of course the best would be developing technologies that produce stuff using less energy. Animal bodies produce a lot of sophisticated compounds never requiring high temperatures of pressures.
miko
