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Bridge of Death (Prypiat) was nominated for deletion. The discussion was closed on 27 March 2009 with a consensus to merge. Its contents were merged into Chernobyl disaster. The original page is now a redirect to this page. For the contribution history and old versions of the redirected article, please see its history; for its talk page, see here.

	Chernobyl disaster is a former featured article candidate. Please view the links under Article milestones below to see why the nomination was archived. For older candidates, please check the archive.
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Pumps, Backups, Chernobyl and the Bible, politics, picking holes in the article, noticing failures in the design and alleviating public fear of nuclear power

Let me point out some little comments of my own in bold type Sorry for my english. (I do not have experience in nuclear plants, but I´ve been working in convencional ones for several years)--Xareu bs (talk) 16:03, 1 September 2010 (UTC) This article will be receiving a lot of views with regards to nuclear plant failures and, so, has the potential to spread a lot of undue negative vibes. I suggest we aim to write it such that it doesn't spread unnecessary negativity about this method of generation. I haven't directly edited the article as I'll undoubtedly be reprimanded by angry critics if I do so. Instead, I'll present my questions in the discussions page.

First of all, 5.5 MEGA watts to run the coolant pumps? Damn! Those must have been some mighty powerful pumps. As I understand it, the backups were being used to power all the emergency systems. That amount of power for even a 28 ton per hour pump is gigantic. If they weren't pumping at high pressures, the 5.5 MW generators will have been used for other systems. You don't need 5.5 MW to move 28 tons per hour at low pressure. If they just had it all in a tower above the reactor, that'd do. Even the normal 30m high towers will produce almost 50psi of pressure and the rooftop tanks will hold two hours worth of coolant at those drainage rates. The purpose built towers will hold more like tens of thousands tons of water. A water tower could have bridged the minutes gap with orders of magnitude left to spare. They could have done away with the backup pumps. I think you are mixing up circulating pumps (condenser cooling), with reactor cooling pumps (primary side on a PWR scheme). 3000 MW of thermal energy is a fair amount of energy to be disipated.

Like my own reply, I believe the description of the backups is long winded, going into details about how a generator works. It would be sufficient to say, the "turbines couldn't provide a stable supply to the pumps".

Why is the chief designers name capitalize?

Why does the section on the tests claim two different test output for the same test?

Why does it then list one test output in mega watts and the second in milli watts. I'd be impressed to see a pile of that size outputting milliwatts. STOP posting in scientific articles if you can't get the unit prefixes right. Yes, it's obvious. No, it's most definitely NOT okay.

Were battery backups and switchmode supplies beyond the designers of a nuclear power plant? The pumps won't have needed 5.5MW alone. They wouldn't even need the switchmode supplies, they could have just chained batteries together. Or built a water tower. I get the feeling they were using a blanket term for emergency power, meaning maintaining all the lights as well as the pumps. They should have had differing levels, blacking the plant out if need be to keep the pumps running. I do not get the point of chained batteries. I do not think you are talking about a DC back up system for such a big power, are you?. As for the water tower/tanks, were they considered in Soviet designs?. Can they cope with the water flow needed to refrigerate a 3000 MW heat exchanger until the diesel units get synchonised and loaded?. "but also to perform a detailed investigation of the bearing."

"The radiation at Level 0 was too high and they ,Popov and Savenkov, received a high (not needed, high has already been used in the sentence) dose that proved to be lethal." Grammar people, grammar.

"As planned, on 25 April a gradual reduction in the output of the power unit was begun at 01:06 a.m., and by the beginning of the day shift the power level had reached 50%." There were four reactors in the chain and the total output on todays modern reactors is around 1GW. Each of the four in the chain would be outputting 1GW. So a 50% reduction would be 500MW, not 700MW and most definitely not 800 milliwatts.

"Further rapid reduction in the power level from 50% was actually executed during the shift change-over." No explanation, no references. Why would they have been doing that?. That´s the issue, a misoperation in a bad moment.

"The test plan called for the power output of reactor 4 to be reduced from its nominal 3200 MW thermal to 700–1000 MW thermal." I may be mixing up thermal with electrical output, but most modern reactors are geared towards 1GW. There were four in this chain, suggesting each was outputting 1GW to reach the chains 4GW total. The turbines are often extremely efficient, so claiming they were thermally outputting four times their electrical output, each, is dubious. What´s the beef with that?. In PWR heat exchangers, only around 1/3 of the thermal megawatts turn into electrical energy in the turbogenerator, and it´s not only due to the losses in the turbine. It´s what a Rankine cycle takes.

"but the low value of the operational reactivity margin restricted further rise of reactor power." That doesn't even make any sense. They mean to say, the reactor wasn't outputting what it should have been with the rods withdrawn.

"The operation of the reactor at the low power level with a small reactivity margin" Why does he insist on saying margin? It doesn't need to be there.

"triggered a trip" Let's try to get inventive with our word selection, please. Triggered an alarm? A warning? An error state? And error status?. A plant trip. Common language in power plants.

"Since water also absorbs neutrons (and the higher density of liquid water makes it a better absorber than steam), turning on additional pumps decreased the reactor power." No mention made of pressures, which have little effect on fluid density anyway.

"All these actions led to an extremely unstable reactor configuration. Nearly all of the control rods were removed, which limited the value of the safety rods when initially inserted in a scram" s I understand things, they actually sent some technicians down to the reactor to pull the rods out entirely; by hand.

"Further, the reactor coolant had limited boiling, but had limited margin to boiling, so any power excursion would produce boiling, reducing neutron absorption by the water." Margin? AGAIN? Simplify to "it was close to boiling". Overly complex, even for a physicist. Yes, it´s rather messy. I do not quite understand why the increased coolant flow rate through the reactor produced an increase in the inlet coolant temperature of the reactor core, I think it should be the other way down.

"The steam to the turbines was shut off, and a run down of the turbine generator began," No need to elaborate on that.

"The diesel generator started and sequentially picked up loads, which was complete by 01:23:43;" The diesel generators picked up the electical load of the pumps and this was completed by.

"it was now primed to embark on a positive feedback loop," Thermal runaway

"However, during almost the entire period of the experiment" Duration

"The reactor was simply being shut down upon the completion of the experiment" Why?

"For whatever reason the EPS-5 button was pressed, insertion of control rods into the reactor core began. The control rod insertion mechanism operated at a relatively slow speed (0.4 m/s) taking 18–20 seconds to travel the full approximately 7-meter core length (height). A bigger problem was a flawed graphite-tip control rod design, which initially displaced coolant before neutron-absorbing material was inserted and the reaction slowed. As a result, the scram actually increased the reaction rate in the lower half of the core." The alternative story I've heard is that in manually withdrawing the rods, they allowed the xeon to escape; causing the subsequent spike. And that it was the rods themselves that melted. Although, having them outside the core makes this unlikely.

"It was not possible to reconstruct the precise sequence of the processes that led to the destruction of the reactor and the power unit building. There is a general understanding that it was steam from the wrecked channels entering the reactor inner structure which' caused the destruction of the fuel casings'; tearing off and lifting, by steam pressure alone, the 2,000 ton upper plate (to which the entire reactor assembly was fastened)."

"excess pressure of vapor." Excessive vapour pressure. I think it should say steam pressure. Vapour pressure is a physic concept for gas-liquid interfaces.

I could go on, endlessly, picking holes in the sentence structure and logic. Instead, I'll simply say, it's too long winded. It routinely tries to make out that things are more complex than they are. Sentences are all over the places and the grammar is not good enough. The guys from Oxford are out there! Watching, bitching. Anyone else for editing the article? I'll do it, but it's a god damn monster. It contains so much useful information, but in a format that is bordering on unaccessible to someone who isn't familiar with the sciences.

"According to another hypothesis, this explosion was of a nuclear nature, i.e., the thermal explosion of the reactor as a result of the uncontrollable escape of fast neutrons caused by the complete water loss in the reactor core. A third hypothesis was that the explosion was caused, exceptionally, by steam." Steam caused the first explosion and the second? The thermal explosion was caused by nuclear reactions? The nuclear reaction heated the water into producing steam? Not same thing.

"According to this version, the flow of steam and the steam pressure caused all the destruction following the ejection from the shaft of a substantial part of the graphite and fuel." What? This is rambling for the sake of it. The cap blew off of the reactor and then the rods blew out? Entirely the opposite of what this sentence suggests. Which suggested the rods blew out and then the cap.

"Parts of the graphite blocks and fuel channels were ejected out of the reactor building"

"However, the ratio of xenon radioisotopes released during the event provides compelling evidence that the second explosion was a nuclear power transient." This is getting boring, even for me. Nuclear power transient? A transient in the levels of nuclear reactivity?

"The nuclear excursion dispersed the core and effectively terminated that phase of the event." What? Rambling?

"Inside reactor 3, the chief of the night shift, Yuri Bagdasarov, wanted to shut down the reactor immediately, but chief engineer Nikolai Fomin would not allow this." Again, no mention of why they ordered this to be so. It was almost certainly due to pressure from the state to keep the reactor functioning; not an unbiased, scientific judgment.

Why didn't the plant have a tower of liquid form moderator ready for this circumstance? I believe even Einstein had bottles of moderator ready to pour on the first pile ever produced.

The article also makes no mention of the official visit the plant had received earlier. Or, the pressure the technicians were under to have it fully operational. Or, the pressure they were under to not embarrass the state with power outages. Placing the entirety of the blame on 'big headed scientists'.

And for anyone about to reply about my own grammar mistakes, this is the discussions page, not an article thousands are using as a reference.

Also not mentioned in the article, but deserving a mention, is that the bible described the star called Wormwood falling to earth and poisoning the rivers, causing bitterness in men. From first hand accounts I've heard that the plant Wormwood is common around Chernobyl.

This article has unfortunately seen a lot of "luvin" from anti-nuclear advocates, attempting to coattrack it to advance their views. You make some excellent points, and I suggest that you be bold and implement some of the changes you suggest. There is nothing wrong with a new editor stepping in and correcting problems. Fell Gleaming 23:55, 11 May 2010 (UTC)

Article prose...

...is not what it once was. I'm not sure exactly what has changed since the last time I had a look, but it's no longer as easily read or as readily understood as it used to be. Is this related to the work discussed above?

J.M. Archer (talk) 19:58, 18 February 2010 (UTC)

Another note, actually:

Some of the modifications made to the text follow logically as responses to the text that was present before the changes were made but make less sense standing here alone. Readers can't be expected to have seen both versions of the text and that's just not the way an encyclopedia is supposed to work: whatever the technical reality is, there is only one Misplaced Pages article on the Chernobyl disaster. It needs to be complete as presented. I've copypasta'd an example below.

All of them returned to the surface and according to Ananenko, their colleagues jumped from happiness when they heard they managed to open the valves. Despite their good condition after the task completion, all of them suffered from radiation sickness, and at least two of them - Ananenko and Bezpalov - died in the process.

This seems almost a non sequitur as presented in the article. It feels out of place in context: there is no reason for the reader to assume they did not make it out, as the article says nothing of the kind. I personally happen to know--and a reader might discover from the article's history page--that this section once claimed that the three divers did not return to the surface and that all died immediately. This snippet seems to make sense as a rebuttal of the older version of the article, but that serves no purpose: there is no reason to rebut a version that is not present, and that the reader has not read.

I can't imagine this being a common practice and would like to see some of these bits and pieces made to fit better within the context of the article but don't necessarily know enough about the event itself to ensure that I can make changes without screwing up details.

J.M. Archer (talk) 20:44, 18 February 2010 (UTC)

Pretty much. "So some things happened, but on the other hand those things didn't really happen, and then other things happened that happened because more things happened, except that things didn't happen because things happened, and who knows what things happened that caused things to happen. In conclusion, 50 people died immediately and 4000 people died later from cancer, but no one really knows how this happened."

But I'm afraid you're completely wrong in thinking this isn't common practice. It's one of the worst, but it's only one example of the round-robin effect of Wiki editing, AKA "Too many cooks spoil the broth". Throw a dozen people in a room with typewriters and axes to grind, and you don't wind up with Shakespeare - you wind up with an uneasy ceasefire after one side outblusters the other, everyone gets something they want thrown in, and all coherency has been lost.

The most flagrant example (of many) demonstrating that 1) people are too scared of starting more flamewars to make meaningful edits and 2) the semi-victorious side was "It was all the fault of the dumb staff and this was blown out of proportion", paraphrased:

Mental health effects: The media scared a lot of people into thinking they were sick. Some people even died from it because they were so scared. The fact that their symptoms from being scared were the same as radiation sickness just goes to show the power of suggestion.

(Amazingly, this has survived over 500 edits despite being patently ridiculous and having no sources to support it.)

Before someone chirps in with the rote "Be bold, be bold, be bold!" claptrap - there are a lot of reasons I gave up on Wikipolitics and became an occasional IP. Chief among them is the fact that "Being bold!" only gets you slow suffocation from well-meaning discussio ad infinitum at best, ulcers and angry stalkers at worst. If you actually think that nothing should be done, isn't "Be bold!" encouraging a person to waste time doing work that someone else will need to waste time deleting? And if you actually agree that something should be done, aren't you saying "Well, yeah, there is a problem - and you should be punished for calling attention to it instead of pretending it's not there like everyone else"? 76.22.25.102 (talk) 15:48, 13 May 2010 (UTC)

For reference, "Mental health effects" in the above comment refers to a subsection deleted in this edit. Somehow, though, I don't doubt that someone will come forward to claim that it was deleted hastily (despite it being up for over half a year with the tag showing it needed sources) and/or that it should be kept while it's discussed for another year or two. 76.22.25.102 (talk) 17:34, 13 May 2010 (UTC)

I echo the sentiments above - without knowing exactly how or what I would do to change it, I do know that this article was once much better written. Slac speak up! 12:22, 19 July 2010 (UTC)

Fallout Comparison

"400 times the fallout". This claim has been tagged as dubious for a while without anyone supporting it. This claim has several problems. First, it is demagogic and overly dramatic in tone. Secondly, the work of SCOPE (see ) suggests such comparisons are impossible; they are inherently "apples to oranges" comparisons. Third, it leaves a false impression in the reader's mind. Hiroshima may have killed as many as 100,000 people from fallout. Yet a release some four hundred times larger has killed possibly as few as 20, and certainly no more than 4,000? Even the source in this case points out that "Early estimates that tens or hundreds of thousands of people would die from Chernobyl have been discredited."

Properly caveated, it might possibly have some relevance elsewhere in the article, but it has no place in the lede. Fell Gleaming 00:11, 20 April 2010 (UTC)

That is basically an argument from personal incredulity, a classic logical flaw. The fact is well-sourced; it comes ultimately from Ten years after Chernobyl: what do we really know?, published in 1997 by the International Atomic Energy Agency (which I'm sure you would accept as an authority). The source states (page 8): "The Chernobyl explosion put 400 times more radioactive material into the Earth's atmosphere than the atomic bomb dropped on Hiroshima." Your "false impression" is, I'm afraid, one that is based on ignorance; Hiroshima killed so many people because it was a nuclear explosion with associated blast, fire and radiation effects. Contamination was relatively minor. That's why the city was rebuilt so quickly. Chernobyl's death toll was almost entirely due to radioactive contamination rather than the initial blast and fire. -- ChrisO (talk) 08:09, 20 April 2010 (UTC)

If the fact comes from the IAEA, it should be sourced to them. In any case, the language as stated is unnecessary dramatic and misleading. I've preserved the material, but placed it in the section describing the aftermath, rather than the lede. Fell Gleaming 14:44, 20 April 2010 (UTC)

The mass of radioactive fallout is both quantifiable and provable. The actual meaning of that much fallout can indeed be apples-to-oranges, but not in the way you suggest.

First, "100,000"? That's the total number of people that died at Hiroshima from all causes, including fire, blunt-force trauma, etc. It's not just the ones who died from radiation sickness, much less sickness caused by residual fallout.

Second, the deaths from radiation sickness at Hiroshima were almost all caused by the dose they absorbed when the bomb went off. As nuclear explosions go, Hiroshima was fairly "clean" for fallout. Abhorrent, yes, but "clean" for fallout.

Third, the deaths caused by X amount of fallout in a concentrated population center will perforce be many times greater than the deaths caused by X amount of fallout in an area that's mostly wilderness. That is the true apples-and-oranges fallacy contained in your argument.

If that statement is being used to evoke the argument "...and therefore Chernobyl killed 400x as many humans", then you would be right in claiming that it's being used falsely. But to claim it should be erased or hidden elsewhere despite its meaning in terms of environmental damage is to whitewash provable scientific fact in the interest of making Chernobyl seem like no big deal. 76.22.25.102 (talk) 16:10, 13 May 2010 (UTC)

Then please someone should add that most of the radiation >99.99% at Hiroshima was caused went the bomb went off, not the contamination. I'm currently working on it.64.18.166.155 (talk) 15:27, 16 May 2010 (UTC)

Chernobyl Nuclear Accident

Neutrality disputed

This article is not by any stretch neutral. It reports a widely criticized, highly contentious report from the IAEA, which is not a scientific organization, as accurate and hardly mentions others criticizing that report. If this article doesn't include reasonable caveats about the IAEA report being heavily disputed, it will be seen as partisan hackery by anybody with ANY level of knowledge of the matter. End of message. —Preceding unsigned comment added by 130.184.253.7 (talk • contribs) 02:31, 3 April 2010 (UTC)

Do you have any references for this criticism? (Blogs and other self-published web sites do not meet Misplaced Pages WP:RS standards) Please give us a few links, if you have them. --Nigelj (talk) 17:58, 28 April 2010 (UTC)

The IAEA's main goal is to promote the use of nuclear energy for power generation. That should definitely be considered. There is a claim in the article that a piece of IAEA data confirms an UNSCEAR piece of data, namely: "In addition, the IAEA states that there has been no increase in the rate of birth defects or abnormalities, or solid cancers (such as lung cancer) corroborating UNSCEAR's assessments."

I don't think this serves to corroborate anything UNSCEAR has said, it is an entirely new piece of information sneaked in under the guise of supporting data. It leads me to question the article's neutrality, at least in this section. While UNSCEAR should be a good source, there should definitely be some caution around what the IAEA say given their interests; at the very least their claims (which are widely contested) should be accompanied by opposing opinions. 192.198.151.36 (talk) 10:00, 4 May 2010 (UTC)

http://whqlibdoc.who.int/publications/2006/9241594179_eng.pdf Here's a link to the WHO report that clearly states the limitations of assessing sold cancer risks (other than thyroid) within a couple of decades of the accident. the conclusion in chapter 5 is a good place to look if you don't want to read the whole thing. 192.198.151.37 (talk) 10:25, 4 May 2010 (UTC)

Apologies for bombing this with comments but I've one more thing to say. I believe the health effects section should not be lead by the mental health subsection. The layout in the WHO report has a much more logical flow. I think being an article about a nuclear disaster it should begin with radiation related effects, perhaps chronologically would work. Actually the reason I came to this talk page to post all this was because I was happily reading the article and when I came to the mental health part I found it poorly written, unsourced, distasteful and potentially offensive. Good day. 192.198.151.37 (talk) 10:37, 4 May 2010 (UTC)

Cooling after a Scram Required?

Challenging second paragraph within the first subsection "Accident". More specifically, "Nuclear power reactors require cooling flow to remove decay heat ... . If not immediately removed by coolant systems, the heat could lead to core damage." This is a lead into the third paragraph that talks about the requirement for forced cooling by use of reactor coolant pumps (RCPs) (although, this is a RBMK, so unsure of the true title of those pumps). It is not true that "nuclear power reactors" need forced cooling after any type of shutdown. They are designed to lose all power, trip the reactor and survive using Auxiliary Feed Water Pumps (AFWP) to maintain water level in the Steam Generators. This maintains a heat sink within the primary loop and will in turn induce natural circulation within the primary loop. That's for PWRs, which is rather different from a RBMK as it's essentially a BWR. I am not an expert with BWRs, so I won't go into them for now. Something for me too look up. But as for PWRs, RCPs aren't even a safety load and are not required for a normal nor emergency shutdown. Hence, "nuclear power reactors" are designed to survive without forced cooling. So this second paragraph is somewhat correct, but vague and misleading, when it generally states that the core needs "cooling flow". Vague because it doesn't say what type of "cooling flow", yes there are two general type in nuclear engineering: natural circulation and forced. Misleading because it continues to talk about how the RCPs for the RBMK are safety loads and are needed after a shutdown.

I propose that we make a small edit to the second paragraph. We need to be more specific to the types of reactors that have this cooling requirement and also to be more descriptive to the type of cooling needed. Gilawson (talk) 17:14, 27 May 2010 (UTC)

Made minor change to 2nd paragraph in bold reaction to your comment. It is safe to conclude that, even though it is a graphite moderated BWR, the RBMK does rely on "coolant flow" to provide decay heat removal. Cheers - Williamborg (Bill) 21:14, 27 May 2010 (UTC)

Not sure what is meant by bold. I will try to read that article more thoroughly to understand it. My point was what kind of "coolant flow". You just restated the vague and misleading statement that a (or in this case any) nuclear power reactor needs "coolant flow". Does the RBMK require forced cooling after a normal shutdown or an emergency shutdown? But what I can tell you is that a PWR Generation II doesn't require forced cooling after any type of shutdown to avoid damage. It seems that a RBMK does and therefore that sentence needs to be changed as it talks about nuclear power reactors in general and talks about this vague concept of "coolant flow". I will edit this paragraph myself after waiting for sometime for more responses and help in this matter. Gilawson (talk) 08:09, 28 May 2010 (UTC)

<== Appreciate your desire for accuracy and precision. My thoughts, combined with recollections from 20 years ago:

• Although I understand the desire for precision, this is an introductory paragraph and emphasis on technical precision may make it more difficult for the average reader to understand key points. That said, Einstein's guidance - to make everything as simple as possible, but no simpler - probably applies here. So let's see what we can do to respond to your request for more precision.
• Most power reactors require continued coolant flow upon scramming after protracted operation for decay heat removal to limit the risk of core damage; the HTGR has sufficient thermal inertia to sustain the thermal transient without flow. The important point here is that the RBMK-1000 requires continued cooling following a scram/trip from power after an extended power run.
• The RBMK is a graphite-moderated pressure-tube boiling water reactor with vertical pressure tubes. So as a boiling water reactor, the coolant flow is actually feed-water flow.
• The RBMK-1000 reactor (all 4 units at Chornobyl/Chernobyl were RBMK-1000s) have two independent primary coolant loops, each cooling half the reactor.
• Each loop has 4 cooling pumps operating in parallel - nominal full power flow of ~2000 liters/second is produced by 3 pumps per loop. The 4th pump provides redundancy.
• Coolant enters the pressure tubes (pipes - the Russians typically translate their term for pressure tube as channel) and flows upward through the core, where it is heated by fuel elements in the pressure tubes.
• Power is removed by coolant heating and phase transition (boiling) as it ascends in the pressure tube - creating a steam-water mix. After passing through a pair of parallel drum-type steam separators, the steam is piped to the turbines.
• From the turbines the condensate is routed back to the feedwater.
• Fission products accumulate during operation at power. The equilibrium level of fission product accumulation depends on power level - primarily on that power level shortly before shutdown. If the reactor has operated at 100% of rated power for an extended period, the decay of fission products produce 7% power immediately after scram - this power decreases with time.
• Following a scram, decay heat is removed by boiling; makeup water (coolant flow) is required during the initial cool-down period.
• The purpose of the test which initiated the accident was to demonstrate that the turbine coast-down could power decay heat removal (i.e., continued coolant makeup) upon a loss of offsite power.

I wish you well in finding a wording you judge is better. Be WP:Bold and make the change to that text when you think that you've got it right.

Cheers - Williamborg (Bill) 03:45, 29 May 2010 (UTC)

I was surprised by your assertion that "But what I can tell you is that a PWR Generation II doesn't require forced cooling after any type of shutdown to avoid damage" but thought I may be out of date. Since this was contrary to my understanding, I did some research. Specifically I reviewed the "Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition (NUREG-0800)". United States Nuclear Regulatory Commission. May 2010. Retrieved 2 June 2010.. Section 5.4.7 titled "RESIDUAL HEAT REMOVAL (RHR) SYSTEM" (Revision 5 which is dated May 2010) deals with decay heat removal in the residual heat removal (RHR) discussion. It specifically discusses using the reactor coolant system (RCS) during and following shutdown and applies to all currently licensed PWRs and BWRs as well as to any new PWR Generation II license submittals. The reference makes it clear that decay heat removal using active coolant flow is required. Just to make sure I did not misunderstand, I spoke with a gentleman involved in the U.S. NRC licensing review of a recent PWR Generation III reactor license submittal (the Advanced PWR (APWR) - nominally Gen-IV PWR from Mitsubishi Heavy Industries) - he assured me that NO Generation II or III reactor design currently exists that does NOT require active cooling for decay heat removal following a scram after extended full power operation. The original wording which you challenged - "Nuclear power reactors require cooling flow to remove decay heat ... . If not immediately removed by coolant systems, the heat could lead to core damage." - remains correct. Hence I doubt that a reference exists for the assertion that "But what I can tell you is that a PWR Generation II doesn't require forced cooling after any type of shutdown to avoid damage." Therefore I will revert the text to the original form.

Skål - Williamborg (Bill) 18:18, 2 June 2010 (UTC)

Took some time, but I got a Final Safety Analysis Report (FSAR) of a Generation II PWR Westinghouse Three-Loop Power Plant. I'm very busy this week, so will make this short, then I will fully address this issue next week. But in the FSAR, it says that you do not need Residual Heat Removal System (RHRS) to maintain Hot Standby, which is Mode 3. Mode 3 is 0% Power, Subcritical conditions (I think it's <0.99, I'll double check that later), and Reactor Coolant System (RCS) temperature of 250 - 350 F (I'll have to double check the temperature). It states that you need AFW in order to maintain the Steam Generators (SGs) as a heat sink and this will create a natural circulation condition sufficient enough to remove decay heat. A SCRAM due to Loss of Offsite Power (LOSP) happens a lot in the industry, the best example is when the North East of USA and areas of Canada had a major blackout. Almost 20 nuclear power plants experienced a LOSP and they all lost their Reactor Coolant Pumps (RCPs) (this applies to PWR). Nuclear power plants don't consider RCPs safety loads, so they are lost and never recovered without Offsite power. Hence, without RCPs, you lose Forced Cooling in your RCS, HOWEVER, there was not one report of core damage from those power plants or any other power plant that is designed to handle a LOSP. Generation II are designed to survive a LOSP event resulting in Natural Circulation of the RCS. Some plants will then choose to return to Mode 1 from Mode 3, or some will decided to move to Mode 5 or further by use of their RHRS. It takes a considerable amount of time to hook your RHRS up to your RCS due to safely depressurizing and lowering your temperature of the RCS. RHRS in general can only operate with the RCS when the RCS is in the 300's in regards to both temperature (F) and pressure (lbs). So I finish this "short" response saying that Generation II PWRs do not require forced cooling to maintain a shutdown condition, or more specifically Mode 3. I will make reference to the FSAR shortly. Your problem is that you loosely refer to a shutdown or use the word "immediately" after a shutdown is just not true. It's very simple and happens all the time: RCPs tripping will cause a Reactor Trip, your RCPs begin to coast down and you start to loose forced cooling as the Reactor is tripping (< 2 seconds). Very soon after you are left with no RCPs running and your rods resting at the bottom of the core and these reactors survive every time, they are designed to according to the FSAR. Gilawson (talk) 21:40, 14 June 2010 (UTC)

I reviewed your source. You are referring to a SRP! That's a guideline for NRC staff! I quote from the documents which is located on the front page of every section, "This Standard Review Plan, NUREG-0800, has been prepared to establish criteria that the U.S. Nuclear Regulatory Commission staff responsible for the review of applications to construct and operate nuclear power plants intends to use in evaluating whether an applicant/licensee meets the NRC's regulations. The Standard Review Plan is not a substitute for the NRC's regulations, and compliance with it is not required." This is a very bad reference to use to justify what a nuclear power plant can and cannot do. But either way, I tried to read into it to find what you were trying to show and couldn't find it. Actually, I found the opposite in section 15.2.1. - 15.2.2. "In all light-water-cooled reactors, sensible and decay heat can be removed through actuation of one or several of the following systems: steam relief system, steam bypass to the condenser, reactor core isolation cooling system (BWR), emergency core cooling systems, and auxiliary feedwater system (PWR)." I hope this shows you that this is a bad reference as it's just a guideline of what NRC staff should adhere to when licensing a nuclear power plant.

I'll copy section 7-4 Systems Required for Safe Shutdown from a FSAR of a PWR in the USA:

7.4 Systems Required for Safe Shutdown* The functions necessary for safe shutdown are available from instrumentation channels that are associated with the major systems in both the primary and secondary of the Nuclear Steam Supply System. These channels are normally aligned to serve a variety of operational functions, including startup and shutdown as well as protective functions. There are no specifically identifiable safe shutdown systems: however, prescribed procedures for securing and maintaining the plant in a safe condition can be instituted by appropriate alignment of selected systems in the Nuclear Steam Supply System. The discussion of these systems together with the applicable codes, criteria and guidelines is found in other sections of this safety analysis report. In addition, the alignment of shutdown functions associated with the engineered safety features which are invoked under postulated limiting fault situations is discussed in Chapter 6 and Section 7.3. For a description of systems required for safe shutdown due to fire, refer to Safe Shutdown Analysis in case of fire (SSA). The instrumentation and control functions which are required to be aligned for achieving and maintaining safe shutdown of the reactor that are discussed in this section are the minimum number under non-accident conditions. These functions will permit the necessary operations that will: a) Prevent the reactor from achieving criticality in violation of the Technical Specifications, and b) Provide an adequate heat sink such that design and safety limits are not exceeded. The modes of shutdown are defined in Chapter 16 as follows:

• Further information is contained in the TMI Appendix.
• Excluding decay heat

7.4.0-1 Amendment No. 50

• • • NPP FSAR

7.4.1 Description Functions required to achieve and maintain the above conditions of shutdown are: a) Proper boration and reactor coolant inventory b) Auxiliary feedwater supply c) Removal of residual heat 7.4.1.1 Systems & Equipment Used for Modes of Shutdown. Systems and equipment used for the modes of shutdown include: (Note: The equipment listed below which is preceded by an asterisk (*) is considered required for the mode of shutdown described. Equipment not preceded by the asterisk is desirable, but not required).
a) Hot Standby

• Auxiliary feedwater system
  
• Boric acid transfer pumps
  
• Steam generator safety valves (No I&C required)
  

Reactor Coolant Inventory Control (CVCS)
Letdown

• Charging
  
• Pressurizer heaters
  

Pressurizer sprays

• Steam generator power operated relief valves
  

Pressurizer power operated relief valves
Reactor Coolant Pump (with auxiliaries)
b) Hot Shutdown

• Auxiliary feedwater system
  
• Boric acid transfer pumps
  
• Steam generator PORV's
  

Reactor coolant inventory control (CVCS)
Letdown

• Charging
  
• Residual heat removal pumps (p < 363 psig)
  

Pressurizer heaters and sprays (if not solid)
Pressurizer power operated relief valves
Reactor Coolant Pump (with auxiliaries)

• Accumulator isolation valves
  

c) Cold Shutdown

• Residual heat removal system
  

Boric acid transfer pumps
Reactor coolant inventory control (CVCS)
Letdown
Charging
7.4.1-1 Amendment No. 48

• • • NPP FSAR
      

Supporting systems and associated equipment required for the modes of shutdown include:

• Component Cooling Water System
  

~* Service Water System
~* Onsite Power Supply System - diesel generators and batteries

• Diesel Generator Fuel Oil Storage and Transfer System
  

26 HVAC Systems/Chilled Water for areas containing equipment required for the modes of shutdown
~* ~ Control Room Panels or Auxiliary Control Panel
* ~ Emergency Lighting

Sorry, the paste and copy was a bit messy, I tried to clean it up as much as I could. I would be interested if you could find a good reference that says that a PWR needs forced cooling immediately after any type of shutdown. Also that a PWR requires forced cooling to maintain a shutdown mode, more specifically Mode 3. But as you can see for yourself, in order to achieve Mode 4 or 5, you do need forced cooling by the use of your RHRS. But again, Mode 3 is a shutdown mode too. Gilawson (talk) 01:38, 15 June 2010 (UTC)

Banana equivalent dose

I just reverted an edit that suggested that the average dose of 600 becs of cesium estimated to have been consumed by wild boars living in the Exclusion zone was the equivalent of eating around 4 kg of bananas - the so-called banana equivalent dose. I've done so because it's a false equivalency - potassium-40 is not the same as cesium, as explained quite well here by Geoff Megitt. I think this would be a comparison that it may be best to stay away from, generally speaking but in this article in particular. Kate (talk) 17:51, 2 September 2010 (UTC)

That "BoingBong" opinion piece source obviously has some reliability issues. To point out just a few of the problems:

• In comparing ingested radioisotopes, the radiologic half-life isn't what's important, but rather the biologic half-life -- the amount of time the material stays within the body. For instance, tritiated water has a half-life of 13 years, but a biologic half-life of less than 10 days.
• K-40 (bananas) and C-137 (radioactive cesium) both emit gamma as well as beta.
• While C-137 does emit a higher ratio of gamma to beta than K-40, they are at a much lower energy level (661 kEV vs 1400 MEV)
• For material biologically absorbed, there is no difference between beta and gamma -- they both have a Q factor of one. Their differing penetrating powers only come into play when dealing with external exposures (since, for example, an alpha particle can be stopped by a single sheet of paper).

In short, the BED comparison is simply to show that a 600 bcq/kg figure is extraordinarily low. Perhaps an even more apt comparison would be to use Brazil nuts, because not only are they even more radioactive than bananas, but because their radioactivity is due to radium, its not homeostatically regulated, and more dangerous than either K-40 or C-137. Letting the reader know that eating a kg of Brazil nuts would be more hazardous than eating a steak from one of these 'radioactive' boars is quite important to put the risks in a neutral, unbiased, unemotional light --- something an encyclopedia has a responsibility to do, but a popular newspaper does not. Fell Gleaming 18:28, 2 September 2010 (UTC)

Comparing bananas and boars is bizarre. I think it is more problematic in another way though. You appear to be trying to make an argument that isn't supported by your sources. I thought that wasn't allowed? (Misplaced Pages:No original research). -- L'ecrivant (talk) 20:26, 2 September 2010 (UTC)

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