Anti-Nukes Claim Zirconium Alloy Will Burst into Flames at VT Yankee
August 22nd, 2010
|
| Share |
Some of the anti-nuclear energy interest groups in Vermont are trying a new tactic against Vermont Yankee, demanding that the NRC order the reactor temperature lowered and thus the power output dramatically cut. Their argument is that the zirconium-based alloy used to clad the fuel can oxidize rapidly (basically burn) at the temperatures the reactor is authorized to run at.
The NRC denied their petition, which is no surprise at all.
NRC says VY temps within limits
BRATTLEBORO — Anti-nuclear activists were denied a petition by the Nuclear Reactor Commission’s Petition Review Board Friday.In a June 7 letter addressed to William Borchardt, executive director for operations at the U.S. Nuclear Regulatory Commission, consultants for the New England Coalition, Mark Leyse and Ray Shadis, requested that the commission lower the limit of the peak fuel cladding temperature at the Vermont Yankee nuclear power plant in Vernon.
Zirconium alloys used in Vermont Yankee’s cladding, which are also commonly used at other nuclear plants across the country, are designed to contain the plant’s reactor fuel, consisting of uranium dioxide ceramic pellets, Shadis said.
“Everything about nuclear safety has to do with containing those pellets,” he said. “The cladding has to retain its integrity to ensure fission products, like strontium-90, never get into the environment.”
The fuel cladding temperature set by the NRC, 2,200 degrees, is far too high to ensure the public safety, according to Leyse and Shadis.
Shadis told the NRC that lowering the temperatures could help ensure an accident similar to the partial core meltdown at Three Mile Island in March 1979, or even worse, won’t occur again.
Experiments and studies conducted in Germany have shown that rapid oxidation, an exothermic reaction where the reaction is self sustaining and generates more heat as the process continues, can occur as low as 1,832 degrees.
“Once rapid oxidation begins there’s nothing you can do about it,” Leyse said. In the experiments, it took only 60 seconds for the temperatures to reach 3,300 degrees because of the runaway oxidation.”
Trying to combat it with water would only make it worse, Leyse added, because the process would just drain the oxygen from the water, rising in temperature.
Based upon the nuclear plant’s analysis, Vermont Yankee is well within the NRC accepted criteria at 2,060 degrees, Entergy spokesman Larry Smith said.
The NRC agreed, which is why the petition was dismissed.
Leyse said the NRC constantly states its purpose is public safety and that it is overly conservative in those measures.
“To be truly conservative, the temperature limits should be lowered to well below the 1,832,” he said.
He estimates that the temperature should be below 1,700 to avoid rapid oxidation.
Leyse said that although the petition was denied, it was passed along to the NRC’s rule making branch for further study and analysis and could be considered for the regulations that govern all the U.S. nuclear plants.
Note: The above article uses the Fahrenheit temperature scale for degrees.
Some background on fuel cladding:
The cladding of most PWR fuel is composed primarily of zirconium. Zirconium alloy fuel cladding typically contains about 98.5% zirconium, with the remaining 2.5% consisting of either tin or a combination of tin, chromium, iron, nickle and other minor components. Up to 5% niobium. is used in the zircalloy used in some Russian reactors.
Zirconium-based alloys have been the primary type of cladding used in reactors since the 1950’s. There are numerous reasons for the use of zirconium, including its high resistance to corrosion and relatively transparency to neutrons. Zirconium has a melting point of 1855 °C / 3371 °F. This is considerably higher than the normal operating temperatures of PWR reactors, providing a good margin of safety in the case of excessive heat.
At extremely high temperatures, zirconium can oxidize. Indeed, zirconium is flammable under the right conditions. As is the case with most other flammable metals (such as aluminum), solid zirconium metal will not ignite easily. If you hold a match to a solid piece of zirconium, it’s not going to catch fire. However, if it is heated to high enough temperatures, provided with an accelerate or ground into small grains it will burn.
There has been some concern over the flammability of zirconium used to clad spent fuel. If very fresh spent fuel were removed from the cooling water it is immersed in, it’s possible that the convection of air would not be enough to keep the fuel rods at a safe temperature. They would become hotter and hotter until eventually the cladding could potentially catch fire. Of course, this would take multiple catastrophic failures to happen and it pertains only to very fresh spent fuel. As spent fuel decays it rapidly becomes less and less radioactive. Cooling with water still helps to keep the fuel at a low temperature and to shield workers from it, but only fuel that is less than a few weeks or, at most, months, has this potential, and even if it did catch fire, only the cladding would burn (the ceramic fuel pellets would still contain most of the material) and contamination would be relatively low and localized and entirely contained within the plant structure.
What Shadis is suggesting, however, is not really the normal type of fire. For the zirconium to burn in the conventional sense it needs air (or at least oxygen). It can’t burn when it is immersed in water in a sealed vessel, as is the case in a pressurized water reactor. What Shadis is claiming is that the fuel could undergo a violent reaction with the water, oxidizing the cladding and producing hydrogen gas in the process.
Something like this happened at Three Mile Island in 1979. The number two reactor suffered a cooling failure, which due to a combination of operator error and systems failure caused the core of one one the reactors to lose coolant. Fuel bundles became partially exposed as water levels dropped and as temperatures increased, a portion of the cladding oxidized and was compromised.
But could this happen in an operating reactor if the temperature went a bit too high?
The book Zirconium in the Nuclear Industry (which can be viewed on Google Books) explains why it cannot. Without getting overly technical, what happened at Three Mile Island was the result of fuel cladding being exposed to an area in the reactor that was not filled with water, as it always should be. The oxidation reaction happened when the fuel was in direct contact with low pressure steam and gaseous hydrogen. (Hydrogen is injected into reactor coolant loops to alter the redox chemistry of the coolant in order to maintain a low-corrosion environment and may also be created by radiolysis) Subsequent experiments with cladding have shown that only in this unique environment will such a reaction occur.
(The image to the left shows the damaged fuel rods in the Three Mile Island reactor)
We can therefore be sure that rapid oxidation of the zirconium alloy cladding will not occur during normal operations when the fuel bundles are surrounded by water in the pressure vessel of the reactor. Even if the normal operating temperature is exceeded, the cladding will maintain its integrity.
Real World Experimental Data on Cladding at High Temperatures:
Zirconium alloy has been the choice for fuel cladding since the 1950’s. In all those years, there has never been a case of the fuel cladding bursting into flames during operation of a reactor, nor has rapid oxidation proven to be a major source of concern in PWR’s, even when temperatures higher than those of Vermont Yankee occur.
In addition to the decades of experience with fuel cladding at the temperatures achieved by PWR reactors, there have been a number of experiments conducted to determine the exact effects of higher than normal temperatures on nuclear fuel and cladding. The LOFT (Loss of Fluid Test) Reactor was operated at the Idaho National Laboratory in the United States from 1963 to 1985. LOFT was designed to use a scaled-down core representative of commercial PWR reactors. The LOFT facility was used to bring these cores to temperatures far beyond their designed operating levels, even to the point of meltdown in order to study the effects of cooling failures on reactors and improve safety.
The PHEBUS facility in France is yet another facility which tests fuel and cladding for nuclear reactors at temperatures beyond normal operations. At PHEBUS, fuel elements are placed in an isolated channel where they are irradiated by a separately-cooled “driver” reactor. The coolant within the channel can be brought to much higher pressures and temperatures than would occur in a reactor during normal operations. It can even be drained completely to simulate a complete loss of coolant.
Thanks to PHEBUS, LOFT and the numerous power reactors that have been running for many many years, we don’t need to rely on theoretical speculation on how cladding might react to various situations in a reactor. We can be certain of the properties of the fuel cladding and its reaction to heat.
But.. what if there’s another Three Mile Island???
As state above, it is possible for cladding to be compromised in the abnormal circumstance of a complete loss of primary coolant. This would never happen in a reactor during normal operations, but it is what happened at Three Mile Island in 1979. A loss of coolant like what happened at Three Mile Island is about the worst thing that can happen to a pressurized water reactor.
Since 1979, a great deal has been changed in order to avoid another incident like Three Mile Island from occurring. Still, it’s impossible to be absolutely certain that an accident of this type will never happen again. Since PWR’s use water to keep the fuel bundles at a safe temperature and remove decay heat, there’s always the remote possibility that, if enough water was lost, the rods could become exposed and another event like Three Mile Island could occur, including compromise of cladding.
But lets not lose context here. Not only are the chances of such an event remote, but at worst, it would lead to heavy internal damage but no danger outside the reactor. Engineers know that reactor vessels could face the stress of uncooled and even molten fuel and design the reactor accordingly. This is why none of the solid material and only a small portion of gaseous fission products ever left the confinement area at Three Mile Island. Nobody died at Three Mile Island; nobody was injured; no property outside the plant was damaged. The reactor vessel was a right-off, but that’s the only damage that happened.
That is about the only circumstance where the rapid oxidation of zirconium alloy cladding might be an issue. If such an event happened at Vermont Yankee or any other PWR, it would not be a disaster – except perhaps for public relations.
This entry was posted on Sunday, August 22nd, 2010 at 7:52 pm and is filed under Bad Science, Enviornment, Good Science, Nuclear, Obfuscation, Politics. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
View blog reactions
September 2nd, 2010 at 12:51 am
The fact of the matter is that your group is out to close down VY, that is your objective, and that was the point I was making. You are not concerned with changes to VT operations or standard practices beyond meeting that objective. To claim anything else is mendacious.
Please understand that we have considered your groups objections and criticisms of VT, and find them without foundation. If you are trying to play to the lurkers here, in the belief that you can convince them that there is any substance to your claims, I think you will find that you are wasting your time, but again, please continue as you are doing more damage to your position, every time you post, than anything I could write.
Quote Comment
September 2nd, 2010 at 1:07 am
ALSO FROM THE SAME NEC WEBSITE PAGE QUOTED SELECTIVELY BY R2D2-
“Finally, our work on watch-dogging VY has to be sharper than ever to get ahead of any further decline in nuclear safety as VY operations and maintenance go into these last few remaining years.”
R2D2-”Please understand that we have considered your groups objections and criticisms of VT, and find them without foundation.”
Quite, pass the crumpets …What pompous twaddle!
…but you may, R2D2, be right about one thing…I could be doing more to damage my position than anything you could ever write.
Thanks,
Ray
Quote Comment
September 2nd, 2010 at 8:45 am
Raymond Shadis said:
For someone who entered this forum complaining about the “unwarranted prejorative [sic] tone and language,” Raymond has a funny way of setting a better example.
I’ve seen this over and over too many times to be surprised anymore. The routine of the hard-core anti-nuke is always the same: Try to dazzle them with BS, and when that doesn’t work, resort to name-calling, innuendo, slurs, and outright insults, all while claiming to be a righteous, disinterested guardian of the public well-being. It’s almost comical.
I’ve listened to too many of these folks speak to not realize that, given enough time, they always reveal themselves for what they are: childish, obnoxious pricks.
Quote Comment
September 2nd, 2010 at 2:05 pm
Raymond Shadis said:
A`summary of the documents referenced.
WASH-740, “Theoretical Possibilities and Consequences of Major Accidents in Large Nuclear Power Plants” (also known as “The Brookhaven Report”) estimated maximum possible damage from a meltdown with no containment building at a large nuclear reactor. The report was published by the U.S. Atomic Energy Commission (USAEC) in 1957.
Far from being conservative in its approach, the assumptions underlying the results were unrealistic. They included the worst meteorological conditions, no containment building, and that half the reactor core is released into the atmosphere as micrometre-sized pellets (without any examination of how this might occur.) At any rate it was superseded by WASH-1400, thus it is obsolete, and cannot be used to infer anything.
WASH-1400, ‘The Reactor Safety Study’ was a report produced in 1975 for the Nuclear Regulatory Commission by a committee of specialists under Professor Norman Rasmussen. It is thus often referred to as the Rasmussen Report. The methodology was comparatively simple and overly-pessimistic by today’s standards, and based on a poor understanding of key phenomenology. Following the Three Mile Island accident, real world data was available to to better model these types of failures and WASH-1400 was declared obsolete, replaced in due course by NUREG-1150.
CRAC-II more properly known as the 1982 Sandia Siting Study or as NUREG/CR-2239, (CRAC-II being the nane of the computer model used for the study, since replaced by MACCS2) is commonly misused as a risk analysis, which it is not. It is a sensitivity analysis of different amounts of radioactive releases. However an SST1 release (an accident of the sort Shadis is implying) is now generally considered not a credible accident by the U.S. Nuclear Regulatory Commission.
Finally, NUREG-1150 (“Severe Accident Risks: An Assessment for Five U.S. Nuclear Power Plants”, 1991, by the Nuclear Regulatory Commission [NRC]) is also considered obsolete, due to inadequate methods and inadequate computer resources in its preparation. The NRC has stated:
“The U.S. Nuclear Regulatory Commission has devoted considerable research resources, both in the past and currently, to evaluating accidents and the possible public consequences of severe reactor accidents. The NRC’s most recent studies have confirmed that early research into the topic led to extremely conservative consequence analyses that generate invalid results for attempting to quantify the possible effects of very unlikely severe accidents. In particular, these previous studies did not reflect current plant design, operation, accident management strategies or security enhancements. They often used unnecessarily conservative estimates or assumptions concerning possible damage to the reactor core, the possible radioactive contamination that could be released, and possible failures of the reactor vessel and containment buildings. These previous studies also failed to realistically model the effect of emergency preparedness. The NRC staff is currently pursuing a new, state-of-the-art assessment of possible severe accidents and their consequences.”
This new report, SOARCA (State-of-the-Art Reactor Consequence Analysis,) will supersede all previous reports.
The bottom line here being that Shadis is practicing dissemination by referencing reports that are obsolete, (and at any rate were never concurrently in force) as if they still had standing.
Quote Comment
September 4th, 2010 at 8:42 am
I’m becoming more and more pro-Nuclear every day. But its primarily people like Shadis who are driving me there.
Quote Comment
October 7th, 2010 at 8:16 pm
Depleted Cranium says:
“If such an event happened at Vermont Yankee or any other PWR, it would not be a disaster – except perhaps for public relations.”
First, Vermont Yankee is a BWR.
(By the way, it’s reported that in the last LOFT experiment, runaway oxidation commenced at around 2060 F. Perhaps you can process that that’s below NRC’s 2200 F fuel cladding temperature limit.)
Second, you may also want to consider: the Zircaloy-steam reaction produces hydrogen.
Third, you may know a little history: think of the Hindenburg.
Fourth, the hydrogen could explode and breach the containment building.
Fifth, before spreading more misinformation, Depleted Cranium may want to look at this: http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1765/
Quote Comment
October 7th, 2010 at 8:33 pm
It’s sad – Dr. Bozo, Steve Packard (he probably thinks yellow cake is something you eat for dessert) and the Bozo wannabes actually think LWRs run at temperatures as high as 2060 F. Packard’s propagating pseudoscience!
Quote Comment
October 7th, 2010 at 8:38 pm
Matte Says:
August 24th, 2010 at 7:24 am
“The runaway reaction of Zirconium in a steam saturated environment is somewhere around 1000 degrees C (1832 F)[ “Nuclear Fuel Behaviour in Loss-of-coolant Accident (LOCA) Conditions”, OECD, 2009].”
Matte – You’re a hack! You evidently don’t know the difference between runaway oxidation and breakaway oxidation! Matte sets himself up like he knows something but he’s obviously just parroting things he’s read without an in-depth understanding!
Quote Comment
October 7th, 2010 at 8:39 pm
On runaway oxidation, the paper Matte cites, “Nuclear Fuel Behaviour in Loss-of-coolant Accident (LOCA) Conditions”, OECD, 2009,” says:
Page 29
“The purpose of the first two criteria, regarding maximum cladding temperature and total
oxidation, was to ensure that the cladding shall remain sufficiently ductile so that it does not shatter
into pieces during and after the quench phase of the LOCA transient. Another important purpose of the
2200°F (1204°C) limit was to ensure that fuel cladding does not enter the regime of runaway
oxidation and uncontrollable core heatup.”
Quote Comment
October 7th, 2010 at 8:40 pm
So “Nuclear Fuel Behaviour in Loss-of-coolant Accident (LOCA) Conditions”, OECD, 2009,” says runaway oxidation begins above 1204 C (2200 F).
On breakaway oxidation, the paper Matte cites, “Nuclear Fuel Behaviour in Loss-of-coolant Accident (LOCA) Conditions”, OECD, 2009,” says:
Page 216
“Figure 6.70, Specimen of E110 cladding that exhibited severe breakaway oxidation after 1400 seconds at 1000°C”
Page 154
“In the interval between 850-950°C, oxide cracking was observed to be much reduced and
transition to a breakaway accelerated oxidation rate did not occur although there was an increase in
rate to a parabolic rate of oxidation. At 1000-1050°C the breakaway type of accelerated oxidation reoccurs.”
So Mate evidently thinks runaway oxidation and breakaway oxidation are one and the same thing! Another victim of a thick cranium!
Quote Comment
October 7th, 2010 at 10:12 pm
This latest duo of anti-nuke commenters Jimbo and Jerry) seem to have exactly the same aversion to competent use of the Quote function as Ray Shadis.
Quote Comment
October 7th, 2010 at 10:35 pm
Hey DV82XL!
The MELCOR Accident Consequence Code Systems (MACCS) code is a piece of junk! Your delusional if you think highly of the predictive codes: think about how well the codes for oil spills predicted the spread of oil in the gulf–pretty piss poorly!
And you ramble on like you’ve never heard of Chernobyl! Yes, I know our nukes are different. But contemplate the Hindenburg. Yes, all the hydrogen produced by the Zircaloy-steam reaction could explode and breach the containment building.
Quote Comment
October 7th, 2010 at 10:45 pm
Jimbo4Chernobyl said:
The only one that is gibbering here is you jackass. Do you honestly think anyone here is going to treat your infantile babbling seriously? You have shown us nothing here except your own uninformed opinions, and steeped in your ignorance of both chemistry and physics.
Basically, you are too stupid to understand the material you are reading, and I am not motivated to bother correcting you in detail, given your poor attitude. If your looking for a fight you will have to find someone else to try and provoke, I won’t be answering you after this.
Quote Comment
October 7th, 2010 at 10:49 pm
Finrod says:
“This latest duo of anti-nuke commenters Jimbo and Jerry) seem to have exactly the same aversion to competent use of the Quote function as Ray Shadis.”
Hey Finrod, who says I’m anti-nuke! I never said I was anti-nuke! I’m 4 nukes!
And I don’t really see Dr. Bozo and his Depleted Cranium site helping the nuclear cause.
Quote Comment
October 7th, 2010 at 10:52 pm
Given their recent appearance, their post timing proximity and their posting styles… Doc, can you do an IP check? I’m thinking we have some sock puppetry going on here.
Quote Comment
October 7th, 2010 at 10:59 pm
DV82XL said:
Ha! Ha! You can’t argue with me because you know nothing about the MACCS code!
As for the tone: Dr. Bozo’s site sets the tone! I guess you just can’t take it when someone spits it back at you!
You’re like Matte, who doesn’t realize that runaway oxidation and breakaway oxidation are two different things–pathetic!
Quote Comment
October 7th, 2010 at 11:24 pm
Jimbo4Nukes said:
Shadis, you would be well advised not to make the mistake of thinking us as stupid as your followers.
Quote Comment
October 7th, 2010 at 11:35 pm
You know, I have stated before that I consider multiple comments in a row to be spam since it makes it floods the conversation, pushes other comments down in the feed and the “what’s hot” section and also is generally just used to be annoying.
Quote Comment
October 8th, 2010 at 6:14 pm
Matthew said:
“Hey Doc! We’ve got another anti-nuke on board! We’ve better smoke ‘em out!”
Yes, Doc, please do do the IP check to confirm I’m not Shadis. Like I said before, Depleted Cranium sets the snarky tone at this site and the snarky pro-nukes can’t handle it when it’s spat back at them. As far as I can see, Shadis has been civil to the pro-nukes in the face of snarky rudeness. And now you attribute my comments to him.
I’m not Shadis. Leave the guy alone. So I would urge Doc, as you call him, to do the IP check to confirm I’m not Shadis.
That being said, all the information I’ve presented is fact-based. I pointed out that Matte didn’t know the difference between breakaway oxidation and runaway oxidation, because he seems to know more than the rest of you. If you can get past my snarky tone (done to match your own), you’ll see that the quotes I provided prove Matte doesn’t know much about oxidation. So if Matte doesn’t know much, where does that leave the rest of you? I want to add that I disagree with many of Shadis’s statements.
Face it, Vermont Yankee is an old piece of junk that should’ve been traded-in in the cash for clunkers program and Entergy would drop it like a hot potato if the Price Anderson Act were abolished.
As pro-nukes you many want to consider that if an old clunker like Vermont Yankee had an accident it would ruin the prospects for safer Gen IV plants being built. Yes, I’m for Thorium.
Quote Comment
October 8th, 2010 at 6:17 pm
Finrod said:
I’m not Shadis. Leave the guy alone. I would urge Doc, as you call him, to do the IP check to confirm I’m not Shadis.
Quote Comment
October 9th, 2010 at 6:16 pm
I’m writing an article for my blog that will attempt to settle once and for all the issue of whether a ‘Chernobyl’ type accident could happen in a modern LWR. The evidence I’ve gathered so far seems to point to the fact that something *That* bad could never happen in a western reactor. However, I’m looking for a paper or study that looks into what the potential consequences of the worst case scenarios for a LWR would be, e.g. containment failure, large release etc. Anyone care to point me in the right direction? There was some mention earlier of WASH – 1400, but then DV82XL pointed out that it was out of date. I looked at NUREG- 1150, but I couldn’t make much of it.
Also, would DC members please take a quick look at my blog and tell me what they think?
Quote Comment
October 9th, 2010 at 7:20 pm
Huw Jones said:
I would if I could find it, Hue. Could you post a direct link?
Quote Comment
October 10th, 2010 at 6:44 am
Ah sorry, I liked it to my name, should have been more clear.
http://fissionenvironmentalists.wordpress.com/
Also, DV8, you seem to be on pretty much every decent blog I come across these days. You wouldn’t mind giving me a list of all the main blogs you post on, would you?
Quote Comment
October 10th, 2010 at 12:52 pm
Huw Jones said:
I posted a comment over there.
Quote Comment
October 11th, 2010 at 4:28 pm
Huw Jones said:
You may want to look at this: http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr1765/
In general, you may want to look up papers discussing “large early release frequency (LERF),” “core damage frequency (CDF),” and “probabilistic risk assessment (PRA).”
Also, NRC has proposed revisions to 10 CFR 50.46(a), which would assign new reactors with different probabilities for CDF and LERF.
Quote Comment