Talk:RBMK

Light water graphite-moderated reactor

Please see comments in Talk:Light water graphite-moderated reactor.

There may also still be material in Light water graphite-moderated reactor that should be incorporated in this entry, but in my judgement the remainder belongs in other entries.

This is explored in more detail in Talk:Light water graphite-moderated reactor. -- Andrewa 10:37 20 Jun 2003 (UTC)

Weapons grade plutonium

I was under the belief that RBMK reactors produced "weapons-grade" plutonium. It seems I was wrong. So, what is the nature of the plutonium produced, and how much processing does it require before being weapons-grade? -- FP 04:33, Mar 4, 2005 (UTC)

When you make plutonium for weapons, you expose U-238 to neutrons, and it turns (indirectly) into Pu-239. If you expose Pu-239 to neutrons, it turns into the useless Pu-240. So the way you make weapons-grade plutonium is by exposing uranium to neutrons for a while (not long), then chemically extracting the plutonium. Easier than isotope separation, but still nontrivial (especially since the various components are poisonous and radioactive).

RBMKs were designed to make this easy by having big cranes to hoist hunks of uranium in and out of the reactor so that they could be exposed to neutrons for an appropriate amount of time; this made it infeasible to have a proper containment structure.

I should say that since reactors are all full of uranium, they all produce plutonium, but when the isotopes are mixed (because of long exposure) and they're mixed with all the other crud that's in a used fuel pellet, it's a real pain to use it for weapons. --Andrew 09:20, Mar 4, 2005 (UTC)

I've added stuff to plutonium explaining some of this. --Andrew 13:11, Mar 4, 2005 (UTC)

Natural or Enriched Uranium Fuel?

There seems to be inconsistency about this in the article in its current state. Midgley 03:04, 2 January 2006 (UTC)

Very much so indeed: how can we conciliate "Thus, a large power reactor can be built that requires no separated isotopes, such as enriched uranium or heavy water" (from the intro) with "... , the concentration of the naturally fissionable U-235 isotope in uranium used to fuel light-water reactors must be increased above the level of natural uranium to assist in sustaining the nuclear chain reaction in the reactor core..." (2nd paragraph of "Design" section) ? Rama 07:44, 21 April 2006 (UTC)

Natural uranium (0.71% U235) can go critical but only with great care in insuring efficient use of the neutrons; you can build a natural-uranium-fuelled reactor if you use pure graphite moderators ( example: Fermi's first reactor in Chicago); so will using heavy (deuterium) water. My understanding is that a light-water reactor with only natural (0.71%) uranium is not feasible. (see X10 amplification experiments in the light-water reactor article indicating insufficient neutron amplification). Also note that because U-235 has a much shorter half-life than U-238, at some point in the gological history of Earth the "natural" uranium was enriched enough that natural uranium and light water could form a successful reactor; this is hypothesized to have happened at Oklo in Gabon about 1.7 billion years ago. Dr. Crash (talk) 13:08, 5 February 2019 (UTC)

Your understanding of the matter is inadequate. RBMK reactors are graphite moderated reactors, with light water as a coolant, not light water reactors which refers to light water moderated reactors. RBMK reactors were designed as natural uranium fueled reactors but were later fueled with LEU for better reactivity control post Chernobyl. Kylesenior (talk) 09:32, 5 July 2019 (UTC)

I can find no reference to RBMK running on natural uranium, always low enrichment: percentages vary, and there is an upward shift after Chernobyl disaster, but it seems that even before the disaster enrichment was newer below 1.8-2% U-235. I suggest that section "History" (section 1) of the Article is edited to align it with section "Fuel" (section 5). — Preceding unsigned comment added by 136.173.162.144 (talk) 10:48, 3 July 2020 (UTC)

The original intent of the designers was to run it on natural uranium to produce either energy or weapons-grade plutonium at low cost (typical cheapskate mentality fostered by the 5-year plans, always try to make everything quicker and cheaper than anyone in the West, in this case at the expense of reliability and safety); however, this proved to be completely impractical because with natural uranium fuel the reactor became almost completely uncontrollable, so they were forced to use low-enriched uranium instead. 2601:646:8A01:B180:B4DA:DC4F:C5F3:9C50 (talk) 09:28, 1 March 2021 (UTC)

There is currently a {{cn}} on this, but I think the whole article needs to be checked to get it right. As well as I know it, they originally ran at about 2%. It might be that early in the design, that it was supposed to be less. Then, after the Chernobyl explosion, it was increased along with some other modifications. I am not sure that the article is now even self consistent. Gah4 (talk) 13:24, 21 December 2021 (UTC)

It goes like this: initially 1.8%, increased to 2% after accident at LNPP, increased to 2.4% after the accident at Chernobyl. It is the initial intention to use natural uranium or lower enrichment that needs a citation.Sredmash (talk) 16:23, 21 December 2021 (UTC)

What exploded

I have removed the words cooling system from the article. They were added by an anon in a recent and so far isolated edit.

But more to the point, they make the article less informative and no more accurate. It wasn't the steam separators or any other part of the cooling system that exploded, it was the top part of the reactor core. What I think this editor is trying to point out is that it wasn't a nuclear explosion, in that (probably) prompt-criticality did not occur (it's hard to say definitively). But this is really splitting hairs; The energy for the first of the two loud bangs certainly came from a runaway and uncontrolled nuclear reaction, and this explosive energy release destroyed the reactor cooling system (and possibly lifted the top plate, again it's hard to say and the experts disagree on which of the bangs actually did this). Andrewa 09:03, 2 February 2006 (UTC)

I work in the nuclear industry and would like to clarify. It has been shown by international authorities that it is most likely that as a result of the massively increased reactor power, the internal core pressure tubes failed, creating a steam explosion which lifted to top-shield off the reactor and causing the cooling pipes located there (the were attached to this sheild) to also ail. To say what exploded hides the actual porgression of the accident.

Okay, who wrote the second part of this section? If you could sign your post, please... it might make your statement more credible... Magus732 (talk) 16:11, 28 July 2011 (UTC)

The complication with this, is that we usually say that a reactor is sub-critical, critical, or prompt critical as one number, but that isn't right. Reactors are much larger than the mean free path of neutrons, so it varies throughout the reactor. As explained in the article, this is more of a problem in RBMK than in the usual PWR. As well as I know it, at least one (maybe small) part of it went prompt critical. As the article says, bringing up an RBMK from zero power is not easy, to keep reactivity balanced throughout, and especially below 10% power. Xenon poisoning after reducing power makes it even harder. Note also that they are not PWR, and so don't have high pressure water, above the 1 atm boiling point, which is the complication of US reactors. Gah4 (talk) 13:33, 21 December 2021 (UTC)

Reactor Class

This is a generation II nuclear reactor (albeit poorly constructed).

Derivatives?

In russian article on this reactor there is reference to a follow-up project, focusing on removing positive void coeff, futher enhancing general efficiency and lowering fuel:power ratio, with ability to generate anuthe radioactive matter, this time not weapon plutonium but rather medicine cobalt http://reactors.narod.ru/mker/mker.html —The preceding unsigned comment was added by 80.249.152.137 (talk) 23:24, 26 April 2007 (UTC).

Neat - they show a full containment and actually use the word "containment" (using Russian letters). Simesa 23:42, 26 April 2007 (UTC)

Stability

What does the phrase "Unfortunately, such a configuration is also unstable." means? What kind of "stability"?... And what about that link to "stability" that doesn't explain absolutely nothing?

Is this simply a reference to the positive void coefficient? This phrase should either be better explained, or removed. -- NIC1138 (talk) 16:57, 22 April 2008 (UTC)

• Maybe it refers to what happened at Chernobyl? I'd find out who wrote it and ask them... Magus732 (talk) 16:07, 28 July 2011 (UTC)

Simple mixtures?

What is said in this article makes me wonder: is it possible to simply take some natural uranium metal or even a naturally occurring uranium mineral, grind it up with boron-free carbon (lamp black?) and dump the mixture into a container whose size would determine how hot it would get? From what is claimed in the article the notion of Neolithic nuclear power (well, heating) doesn't seem so impossible. Wnt (talk) 21:22, 18 May 2008 (UTC)

Forget neolithic, check out Natural nuclear fission reactor. --96.241.226.166 (talk) 22:45, 14 March 2011 (UTC)

RBMK-1000 or MKER-1000?

MKER says that Kursk-5 is an MKER-1000 - a newer version of RBMK with a full containment structure and passive safety. This page says that Kursk-5 is an RBMK. Which statement is true? --Tweenk (talk) 19:43, 23 November 2009 (UTC)

Kursk-5 is an RBMK-1000. But the active zone of the reactor also the physical characteristic is like an MKER-1000. Any person always deletes in the article MKEK the word physical before the word prototype. Greetings ChNPP (talk) 09:46, 5 January 2010 (UTC)

List of references for locations of detonations

Is the above phrase in reference no. 26 a vandalism? 83.149.209.253 (talk) 15:14, 6 October 2010 (UTC)

Yes, it is vandalism. I delete the sentence. Best Regards ChNPP (talk) 16:46, 6 October 2010 (UTC)

Erroneous containment system values

"The reactor vessel is a steel cylinder with outer diameter of 14.52 m (47 ft 8 in), wall thickness 16 m (52 ft 6 in), height 9.75 m (32 ft 0 in), and is equipped with a bellows compensator to absorb axial thermal expansion loads."

A wall thickness greater than the outer diameter of the vessel? I don't know where I'd find more accurate data, but this is clearly incorrect. 82.41.24.25 (talk) 01:24, 23 May 2011 (UTC)

The proper thickness is 16mm, not 16m; I just fixed it. It was broken on 03:48, 23 April 2011 by an edit which added the convert templates. -- 203.82.93.98 (talk) 12:45, 28 July 2011 (UTC)

Yeah... I don't know how I missed that... Magus732 (talk) 16:09, 28 July 2011 (UTC)

Light water vs. heavy needing enriched fuel

In the design flaws section it is incorrect to state that heavy water requires enriched uranium "because it does not absorb neutrons". The opposite is true, light water requires enriched uranium for neutron economy. CANDU reactors are a prime example of using heavy water to enable use of unenriched uranium. The author has already stated the correct reason for using graphite rather than heavy water as a moderator, that being that heavy water is rare and was being used for military applications. — Preceding unsigned comment added by 216.218.29.239 (talk) 17:56, 2 March 2012 (UTC)

Graphite Tips

What was the motivation behind this design feature of the control rods? This must have had some sort of intended purpose, otherwise as it being counter intuitive would not have made it into the design. Hogdotmac (talk) 03:44, 30 May 2012 (UTC)

This information is already in the article and was so on the 30th May. 86.156.154.237 (talk) 11:17, 29 August 2012 (UTC)

Thermal ratings

The thermal output of the reactor plants is missing. The RBMK-1000, for example, is rated for 1 GWe. The little "e" is electric output. Not to be technical, but this is a very important little "e" that is likely misunderstood. It should be a subscript, not kust little.

Anyway, I would assume that the thermal output is around 3 GW. Or I should say 3 GW_t. I like to saw logs! (talk) 07:45, 15 December 2012 (UTC)

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Power coefficient

The article does not currently mention the positive power coefficient (short for power coefficient of reactivity) as far as I can see, just the void coefficient. It is the combination of these two, rather than either on its own, that made the RBMK reactor highly unstable, as I understand it. Andrewa (talk) 20:24, 16 October 2017 (UTC)

Graphite rings cool the graphite blocks

The article stated the graphite rings transfered 80-85% of core thermal power. Reference 9 (group II question5) explains that these rings cool the graphite blocks, transfering approximately 80-85% of the energy deposited in them to the pressure tubes. It further clarifies that only about 5.5% of rated thermal power is from the graphite. Robot1marvin (talk) 19:59, 18 February 2018 (UTC)

Number of reactors still in operation

according to the IAEA, there are still 15 RBMK reactors running in Russia, with a rated power of 10219 MWe. This does not relate to the power output of around 950 MWe per reactor, and also does not specify the location of each. In this wiki, 11 are said to be running. What would be the correct number?¬¬¬¬ — Preceding unsigned comment added by Fsikkema (talk • contribs) 12:42, 1 June 2018 (UTC)

I think the IAEA also includes the reactors at Bilibino Nuclear Power Plant, scaled down versions of the RMBK reactor. --Ita140188 (talk) 08:06, 3 June 2018 (UTC)

References

Chernobyl unit 1 power

When I looked at the table of reactors I saw that chernobyl block 1 had a reduced power rating than the others is their a reason for this?

Shortened rods

Were the shortened control rods from below the reactor under the control of the RCPS and/or the EPS system, or were they under manual control only? Were they inserted into the reactor by pressing AZ-5? 2601:646:8A01:B180:B4DA:DC4F:C5F3:9C50 (talk) 09:17, 1 March 2021 (UTC)

Shortened (UPS) rods were under manual control and not inserted upon an EPS signal.Sredmash (talk) 16:20, 21 December 2021 (UTC)

Unusual design

I do not see the addition to the intro paragraph as an improvement in its current form. First of all, the wording is awkward and unclear, and the added information would be better off in its own sentence. Factually speaking, I am reasonably certain there were more than two reactor types in development in the 1970s. More importantly, the quoted opinion from the article is rather tendentious, given that a double digit percentage of reactors extant in the 1970s were also graphite moderated with fuel in channels. The very first reactors (and most military reactors) in the world were in this sense similar to an RBMK. So any use of this source to refer to the RBMK's unusual design should contextualize it in terms of civilian reactors. And in any case it would be better off placed in the body of the article.Sredmash (talk) 16:54, 24 April 2024 (UTC)