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Pastimes : Let's Talk About Our Feelings!!! -- Ignore unavailable to you. Want to Upgrade?

To: Jacques Chitte who wrote (21283)	5/4/1998 5:47:00 PM
From: LoLoLoLita	Respond to of 108807

Alex, Yes, MOX can be used in a HTGR, a reactor concept that can have "walk away" safety if it's done right. MOX can also be used in the proposed "Advanced LWRs" from Westinghouse, GE, and the other vendors. I'm not a nuclear engineer, so I'm not familiar with the exact details of how a reactor core is modified to switch between different types of fuels with different neutron spectra, but the basic idea is that in order to have a stable chain reaction, a certain amount of material must be present to slow down the neutrons sufficiently, and hit enough of the fissionable material in the fuel to maintain a steady chain reaction. But I do know that over the course of recent years, the core loading of conventional LWRs has been modified to use fuel of higher enrichment than in the original configuration. This has allowed a higher "burnup" of the fuel, meaning they get more energy out of the same mass of fuel. Detailed neutron transport calculations using validated computer codes are performed to make sure there will be a proper level of moderation in the core after making any of these changes. The correctness of these simulations is easily verified by measuring the neutron flux in the actual reactor after the fact. As hinted at above, depending on the type of fuel, the quantity, placement, (or maybe even the type) of moderator can be varied to suit. One advantage of the CANDU reactor over all of the LWR concepts is that the fuel is natural uranium with the isotopic mix found in nature. There is no need to have U enrichment plants, which operate by converting the uranium to uranium hexaflouride, and then running the gas through a separation cascade to raise the U-235 concentration. And the reactor moderator, in this case, is non-radioactive heavy water that is obtained by isotopic separation. As a chemist, I'm sure you will agree that the hazards of separating out heavy water should be vastly smaller than the hazards of separating U-235 from the hexaflouride gas. I do not know if the CANDU design can be, or is, used with MOX. There are quite a few good candidates for a "safe" reactor. And I do have to agree with you that the HTGR has some very desirable characteristics from the standpoint of safety. Bear in mind that there are other candidates. The reactor vendors have all been engaged in competition, and safety is a selling point. None of the vendors want to be seen as selling unsafe reactors. David

To: Jacques Chitte who wrote (21283)	5/4/1998 6:20:00 PM
From: LoLoLoLita	Respond to of 108807

Oh, forgot to mention. The hot topic with MOX these days is whether or not we should use it as a way of using all the weapons grade plutonium taken out of the bombs we don't need anymore. That would be the easiest way to start using MOX. When those stocks ran out, we could get the Pu from recycling spent fuel. DOE is doing a whole bunch of EISs on this. Also, there is a National Academy of Sciences report on what to do with the weapons plutonium. If you want to dig deeper on this, look for the EISs starting at doe.gov One of them is called "Storage and Disposition of Weapons-Usable Fissile Materials Environmental Impact Statement," DOE/EIS-0225. All the descriptions of what they could do with MOX should be there, or referenced from there. If you have a DOE reading room nearby, they may have these documents, or they might be on the web. Or you could purchase them from NTIS if DOE has run out of the free copies. The Draft EIS was issued in 1996. I don't know if they have a Final yet. You can probably find out a lot by searching the Federal Register, from gpo.gov All the EISs and Records of Decision (RODs) can be found there. Let me know if you find anything interesting, or puzzling. David