neal@lynx.uucp (Neal Woodall) (08/29/89)
In article <2243@jane.uh.edu> CHEEHH@jane.uh.edu (Rikhit Arora) writes: >In response to my original queries regarding Galileo's RTG's, Henry >mentioned that one should get rid of RTG's altogether and switch to >nuclear reactors. Well, what exactly is an RTG then? It *is* called >a Radioisotope Thermoelectric Generator. How much different is it >from a genuine nuclear reactor? I am going to work from old memories here....a nuclear reactor is a device which uses the neutron emissions of certain radioactive elements to build up a nuclear chain reaction (you know the old stuff....one neutron causes multiple neutrons, each of which causes more multiple neutrons, etc). In the case of a nuclear reactor which generates electricity, the reaction is moderated by some control rods made of cadmium (which is a "hungry" neutron absorber), else the reaction can get out of hand and meltdown! These things are tricky to moderate, and need an active control system to keep them from going super-critical. The RTG's used in spaceflight are probably based on nuclear fuel that does not emit neutrons, and therefore cannot start a nuclear chain reaction. The decaying nuclear fuel will emit large ammounts of energy for a long time, but there is no chance of a runaway reaction and its possible consequences. Because there is no "chain reaction" possible, there is no need for an active control system, and the thing is both simpler and safer than a real reactor. Of course, the power output is lower, but you don't get something for nothing. Any comments from net.land?? >And what technical difficulty >prevents NASA from using a real nuclear reactor for these deep space >probes? Probably that they are too tricky to moderate (needs that active control system) and there are more failure modes, some of them catastrophic! Neal