tag:blogger.com,1999:blog-7597656451205429515.post7245646526384790847..comments2024-02-16T17:52:44.944-06:00Comments on The Nuclear Green Revolution: A Primer on Nuclear Safety: 2.5 Defense in DepthCharles Bartonhttp://www.blogger.com/profile/01125297013064527425noreply@blogger.comBlogger6125tag:blogger.com,1999:blog-7597656451205429515.post-21383796483752684262008-12-17T04:07:00.000-06:002008-12-17T04:07:00.000-06:00The comments describe some of the developmental pr...The comments describe some of the developmental problems with the PBMR. I believe that the problems can be overcome, but the PBR does not have the potential of the LFTR.Charles Bartonhttps://www.blogger.com/profile/01125297013064527425noreply@blogger.comtag:blogger.com,1999:blog-7597656451205429515.post-44132669087312250402008-12-17T03:39:00.000-06:002008-12-17T03:39:00.000-06:00It is not just as easy: The friction of graphite i...It is not just as easy: The friction of graphite in HTRs is much larger than in ambient conditions. This is because graphite is a lubricant only, if it is covered by a thin layer of oxygen. This layer vanishes in hot Helium. Unfortunately this was not considered in German pebble bed reactor design. <BR/>Large friction means large dust production, irregular pebble flow and local pebble bed densification. In the THTR300 pebble bed reactor the pebble flow was completely different from precalculations: There was only flow in the reactor axis, but not adjacent to the walls. That led to high temperatures in the axis, which damaged by hot gas streams the metallic hot gas duct. At the end the pebble flow was abandoned during full power operation and allowed only on sundays, when low power operation was possible.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-7597656451205429515.post-57892674281981700242008-12-05T12:35:00.000-06:002008-12-05T12:35:00.000-06:00Well, you don't have to be a German engineer to be...Well, you don't have to be a German engineer to beat gravity. This is done thousands of time by airplanes; simply letting the forces on wings be net positive (at climb), which is achieved through the remarkable equation F=p*A. Reversing the flow of balls could simply be done by letting outlet pressure increase inlet pressure + gravity.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-7597656451205429515.post-16496696534297567312008-10-16T19:48:00.000-05:002008-10-16T19:48:00.000-05:00Charles, I have a question about PBMR's that I've ...Charles, I have a question about PBMR's that I've been wondering about for some time. I read somewhere about the German reactor having a problem with a jammed pebble which helped terminate the program. As your diagram shows, the PBMR resembles a gumball machine. I can remember putting a dime in the gumball machine and pounding it on the side to get an extra gumball. I would hate to think that PBMR reactor designs could not resolve the mechanical problem of spheres going through a tube or other dispenser. So my question is, do you know if any mechanical engineering or other advances that overcome the possibility of the jammed pebble problem the Germans had?Jason Ribeirohttps://www.blogger.com/profile/06863185203119704249noreply@blogger.comtag:blogger.com,1999:blog-7597656451205429515.post-81698471042647439132008-10-16T12:59:00.000-05:002008-10-16T12:59:00.000-05:00This differs from the first illustration where the...This differs from the first illustration where the gas flow is from top to bottom, which along with gravity would tend to hold the pebbles in place. - Donb<BR/><BR/>Arn't those German engineers amazing?Charles Bartonhttps://www.blogger.com/profile/01125297013064527425noreply@blogger.comtag:blogger.com,1999:blog-7597656451205429515.post-58636837389541213302008-10-16T10:18:00.000-05:002008-10-16T10:18:00.000-05:00The original post states:The German Pebble Bed Rea...The original post states:<BR/><I>The German Pebble Bed Reactors had one remarkable feature that is repeated in reactor developed from the PBR concept. The pebbles were blown into the reaction chamber by helium gas, and suspended within the reaction chamber by the gas flow.</I><BR/>Intersting. This differs from the first illustration where the gas flow is from top to bottom, which along with gravity would tend to hold the pebbles in place.<BR/><BR/><I>PBMR advocates are so confident in the safety of the reactor (some even call it "meltdown-proof") that they have proposed a drastic weakening of a number of safety requirements that apply to the current generation of U.S. nuclear plants.</I><BR/>I would want to see several reactor-centuries of operational experience before reducing containment building requirements below that currently used for light water reactors.<BR/><BR/>One more thing. I think it was Rod Adams who observed that there simply is not enough helium in the world to deploy helium cooled reactors on a massive scale. That is one nice thing about the LFTR - the cooling gas does not flow through the reactor, so other gasses (e.g., nitrogen) can be used.Anonymousnoreply@blogger.com