Loading AI tools
From Wikipedia, the free encyclopedia
![]() | This article is rated C-class on Wikipedia's content assessment scale. It is of interest to the following WikiProjects: | ||||||||||
|
![]() | It is requested that a mechanical diagram or diagrams be included in this article to improve its quality. Specific illustrations, plots or diagrams can be requested at the Graphic Lab. For more information, refer to discussion on this page and/or the listing at Wikipedia:Requested images. |
|
|
How does it work? Are the pebbles hot for themselves, the reaction occurs (mainly?) in the pebble, or are neutrons going from one pebble to others. If second case, how radioactive are the pebble before and after irradiation? And in this case, isnt there a possibility to stop the reaction in case of necessity in draining the core? If first case, are the pebble usable in little amounts like in a thermal-electricity-generator like those used in space? What is the operating life-length of a pebble? I think these are quite important topics that the reader wants to know... Pipecat (talk) 16:13, 15 April 2011 (UTC)
The company in South Africa that is developing the PBR always appear to gloss over the safety concerns in an attempt to minimize them in the eyes of the public. I personally think this technology is viable, but when playing with nuclear power, one shouldn't ever downplay the risks.
There is a strong likelihood that this Wikipedia article is being modified by a public relations company, or an expert in PR. —Preceding unsigned comment added by ObseloV (talk • contribs) 04:57, 21 January 2009 (UTC)
For anyone who's wondering about the change in emphasis between the old reactors and the PBR designs, the PBR is using the "Chicken McNugget" business model, you put all your high technology investment up-front into the material manufacturing (the "pebble factory"), and then you can set up cheap franchised outlets wherever you want, taking delivery of the high-tech pebbles, bunging them into cheap reactors, and serving up hot and tasty electricity using staff who don't have to be geniuses, and who don't get the chance to do anything potentially dangerous.
Someone who used to design structural steelwork for UK reactors once said that they were designed like cathedrals: every one was different. It's like the restaurant business: you can have a single restaurant with specialist equipment and staff, all working together to create a great product and avoid food-poisoning disasters, but when it comes to franchising it, you have problems: You can't easily duplicate key staff, monitoring quality control through the chain is difficult (so you get stupid accidents) and you don't get bulk deals on the key equipment. You may get an economy of scale regarding know-how, but not for staff or hardware, because you aren't intending to build that many restaurants, and all your equipment is still very specialised.
The alternative is the McDonalds approach: to redesign the entire business model around mass production and franchising. Design once, build many (but spend a lot of money on the design). MacDonalds is the home of the Chicken McNugget: It takes a product that is variable and messy, and needs to be handled with care (chicken) and it turns it into a centrally-produced, encapsulated, idiot-proof format. You move all your high-tech staff and plant and specialist equipment into a central location where you use computers and robots and liquid nitrogen and god knows what else to churn out "nuggets", then you ship the nuggets to your local franchises, where the cheap staff dunk them in hot oil and serve them. The local staff never get to touch a knife or a piece of raw chicken themselves.
With cheap local staff and simple local plant, and there's a limit to how badly they can mess things up, because their job has already been made as simple as possible. You try to think of everything beforehand and streamline the local processes to be as close to idiot-proof as possible. The guys with the tough job are the ones back at the nugget factory (or the pebble factory) -- the cost and consistency of what happens there dictates the viability of the entire chain. If the mass-produced designs are right, and the product is designed well, the system runs smoothly and efficiently. If there's a problem at the nugget plant, it affects the whole chain. So it's critically important to get everything right (or nearly right) before you take the thing into mass-production.
This is why we haven't already had a big PBR roll-out: they want to hold off and make sure that they get it right, and then if a few pilot plants show that the model works, and there aren't any further cost or reliability issues with the pebbles ... poom ... the things will be everywhere. But the integrity, durability, reliability, manufacturing safety and cost of the pebbles themselves is critical. ErkDemon 16:22, 22 May 2007 (UTC)
I just tried to access reference 9 but it appears to have 404d... 87.112.74.244 (talk) 11:46, 3 January 2008 (UTC)
In section Pebble_bed_reactor#Safety_features, it says:
Later problems with the AVR reactor resulted in a small release of radiation to the public.
I really think we need a citation for this event to clarify just how safe or unsafe these reactors are. I would also like to see information on exactly how "small" it was, if that information can be found.
The best reference I found in Googling is at the end of a page on how pebbles circulate within the reactor, but it is still very vague, and not a very authoritative source. Another potential reference is Reactor Watchdog Project's info page on PBMR, which has more detail, but also comes from a site with an obvious anti-nuclear spin.
It is also mentioned in THTR-300#Decommissioning, but I don't see a citation there either.
Different sources identify the event as happening in 1986, 1988, or May 4, 1985.
Correct is May 4, 1986 —Preceding unsigned comment added by 80.137.39.188 (talk) 10:00, 14 October 2010 (UTC)
LeBleu (talk) 00:44, 4 February 2008 (UTC)
The NIRS is not a credible source. I have removed the link. —Preceding unsigned comment added by 70.162.2.55 (talk) 00:09, 17 November 2008 (UTC)
Also, it is very difficult to get exact information on these accidents, since most of them have to do with national security interests. 128.196.210.75 (talk) 22:35, 17 November 2008 (UTC)
Articles like this give me the impression that potentially, a shaman would need merely mix a powdered mineral containing unenriched uranium with a pure lampblack in order to make an ever-burning fire. (Though some ill might have befallen some villagers burned with it, he can scarcely be blamed for the judgments of the gods) Is it plausible for people to have made reactors this way in Neolithic times? Wnt (talk) 22:06, 7 August 2008 (UTC)
A pile of "spent" pebbles will still get hot, right? It seems like if the issues with cesium and strontium leaking out could be resolved, one could dump them in a sea with circulation issues to circulate the water by heating the depths. 65.46.169.246 (talk) 15:07, 16 March 2011 (UTC)
What are the typical dimensions of the pebbles used in such reactors? This should be included in the text of the Design section, as now it seems one can only roughly deduce their size by looking at one of the pictures. —Centrx→talk • 05:21, 18 November 2008 (UTC)
6 cm in diameter is what AVR, HTR-10 and THTR used. Other sizes have been discussed (Someone from MIT put out a paper on this, but I don't remember the exact reference Kadak and others 2004ish maybe?) The pdf you can get from http://hdl.handle.net/2128/3136 has the pebble dimensions on page 2 for AVR. Jrincayc (talk) 03:39, 20 November 2008 (UTC)
Section "Safety Features", final paragraph contains the text "The graphite is the moderator for the reactor, and are strong containment vessels", which defies grammar and seems meaningless. —Preceding unsigned comment added by 212.159.59.5 (talk) 18:33, 27 February 2009 (UTC)
Lots of logic probelms. I think a lot of this was written by someone who wasn't that skilled at english and worked in a hurry. consider this last sentence that I found:
The THTR management continued to charge the Chernobyl fallout for all the contamination in the surrounding, until the presence of Pa-233 ... 233Pa is not formed in uranium reactors as Chernobyl, but only in thorium reactors .... Thus, step by step, the THTR management report was accurate.
I'll clean this up but a once-over by someone who knows would help. OsamaBinLogin (talk) 00:10, 21 May 2012 (UTC)
There's a scattering of [citation needed] markers -- any chemists out there who can assist? E.g.:
This paragraph ...
"A pebble-bed reactor thus can have all of its supporting machinery fail, and the reactor will not crack, melt, explode or spew hazardous wastes. It simply goes up to a designed "idle" temperature, and stays there. In that state, the reactor vessel radiates heat, but the vessel and fuel spheres remain intact and undamaged. The machinery can be repaired or the fuel can be removed. These safety features were tested (and filmed) with the German AVR reactor.[10]. All the control rods were removed, and the coolant flow was halted. Afterward, the fuel balls were sampled and examined for damage and there was none."
... is in contrast to ...
"Darüber hinaus wurde im Jahre 2008 ein Bericht von Rainer Moormann, Mitarbeiter des FZJ, veröffentlicht, in dem die übermäßig starke radioaktive Kontamination des Reaktors auf eine unzureichende Überwachung des Reaktorkerns sowie einen länger andauernden Betrieb bei unzulässig hohen Temperaturen zurückzuführen ist. Dies habe u. a. dazu geführt, dass Spaltprodukte aus den Graphitkugeln austreten konnten."
... from http://de.wikipedia.org/wiki/AVR_%28J%C3%BClich%29 , which translates to ...
Furthermore in 2008 Rainer Moormann, who works at the FZJ, published a report where the overly high contamination of the reactor was caused by inadequate monitoring of the reactor core as well as by lengthy operations at inadmissively high temperatures. This has among others led to the release of fission products from the graphite balls.
Is Rainer Moormann's report correct? Did the pebbles leak due to excess temperature? What is excess temperature? I thought the reactor can go up to idle temperature which is not excessive and safe. Or was the leakage caused by additionally leakage of water into the reactor? —Preceding unsigned comment added by Darsie42 (talk • contribs) 15:31, 18 July 2010 (UTC)
Reference 6 returns a 404 error mostly in German. Some sleuthing may be required to find the correct new link. —Preceding unsigned comment added by 65.160.229.33 (talk) 17:01, 14 March 2011 (UTC)
The article emphasizes at various spots that there are no control rods in this reactor design; however, later, it states:
"All the control rods were removed"
How does that fit together?
Intrr (talk) 19:14, 26 March 2011 (UTC)
Answer:
Every reactor design has some kind of manual mechanism to control neutron absorption. The most common is control rods inserted into the center of the reactor, alongside the fuel rods. In a pebble bed reactor, this is clearly not a good idea. The alternative is to surround the fuel area with neutron reflecting material, and alter this material in order to control the amount of neutrons in the core. One design uses rotating cylinders, which are neutron reflecting on one side, and neutron absorbing on the other. Another method would be to have a solid block of neutron reflecting material, with spaces where neutron absorbing material can be slid into place. These sliding neutron absorbers are different from conventional control rods, but could also be reasonable described as control rods. I do not see a contradiction here, just vagueness.
Probably the details of the PBR design should be researched, properly referenced and described. However, the information in the article regarding control rods seems basically correct, though technically vague. The article mentions the sliding neutron absorbers, but does not specifically say that the PBR design used them.
Anyway, the whole point of the PBR design is that conventional neutron control systems are not needed for safe operation. So this control rod discussion is not all that important.
-Anon, March 28
I would have to say that the statements about graphite burning are the results of original research. There are no citations regarding this. It was just presumed that because it was a form of Carbon that it would readily burn.
In fact, graphite is not combustible, or only slightly combustible at high temperatures. There is also pyrolytic Carbon that is also used in making TRISO fuel elements that is only combustible at high temperatures. Some actual research should be done on the subject regarding just how combustible graphite is under the temperature conditions in the reactor.
Tyrerj (talk) 06:00, 23 January 2015 (UTC)
The article says: "it is difficult to re-use pebble-bed reactor waste for nuclear weapons"
Since it is impossible to make nuclear weapons from reactor "waste", that really makes no difference. Reactor waste contains Plutonium. However, it is what is called reactor grade Plutonium. If you read Wikipedia, you will find that there is more than one isotope of Plutonium and that only Plutonium-239 is desirable for making weapons. Plutonium that contains over 10% of Plutonium-240 is simply not suitable for making weapons. The Plutonium in reactor waste not only contains more than that much 240 but also contains 241 and 242. I suggest that you do some research instead of repeating incorrect anti-nuclear propaganda.
Tyrerj (talk) 06:27, 23 January 2015 (UTC)
"In spite of the limited amount of radioactivity released (0.1 GBq 60Co, 137Cs, 233Pa)a commission of inquiry was appointed. The radioactivity in the vicinity of the THTR-300 was finally found to result 25% from Chernobyl and 75% from THTR-300."
This is incorrect and probably a lie coming from an editor who should know the final report of that commission. It rejected all claims coming from anti-nuclear-power-activists regarding the 75 % as unfounded. It actually states that the activity in the vicinity coming from the plant was so small that it could not be measured and was not detected by the installed measuring stations and estimated it based on the measured emissions(!) of that week using a distribution model to be less than 1 Bq / m² of soil surface at maximum (while the immissions(!) coming from Chernobyl in that area at that time being around 10000 Bq / m²).
The final report of that commission:
https://www.landtag.nrw.de/portal/WWW/dokumentenarchiv/Dokument?Id=MMV10%2F561%7C1%7C0
Jwalter (talk) 08:24, 31 May 2016 (UTC)
Project Timberwind used particle-bed reactor designs - are they considered pebble-bed reactors ? - Rod57 (talk) 17:40, 15 April 2021 (UTC)
There seems to be a problem with the sketch of the reactor. Where does it come from? There's no source listed. Here's what I found disturbing: the arrows that illustrate gas circulation and these arrows suggest that the cooling gas is forced down the pebble bed and then down through the heat exchanger which is the opposite of natural gas circulation due to temperature and density changes. Without pumping, the gas would heat and rise in the reactor and cool down and fall in the heat exchanger. This natural circulation seems like a fail-safe for the pumps. Also, forcing the flow down through the pebble bed could cause convection heat bubbles to form - the hotter the area, the more it would resist the forced downwards flow (the opposite would happen in the exchanger, though there the linear structure and coolant flow make it much less relevant). - not signed by User:78.11.145.7 06:18, 26 July 2021
Seamless Wikipedia browsing. On steroids.
Every time you click a link to Wikipedia, Wiktionary or Wikiquote in your browser's search results, it will show the modern Wikiwand interface.
Wikiwand extension is a five stars, simple, with minimum permission required to keep your browsing private, safe and transparent.