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Posted on 12/30/2005 8:04:29 PM PST by grundle
NRC OKs Westinghouse nuclear plant design
Westinghouse Electric Co.'s nuclear plant design using pressurized water was approved Friday by the Nuclear Regulatory Commission, a move the company said could lead to the first construction of a nuclear power plant in the United States since before the Three Mile Island accident in 1979.
Pittsburgh-based Westinghouse's Advanced Passive 1000 nuclear plant design uses pressurized water to fire the plant. France's Areva also has a pressurized-water design, while General Electric Co. uses a boiling water model.
In a statement, Westinghouse senior vice president Daniel Lipman said the action was a positive step.
"Westinghouse is certainly pleased to have achieved this latest milestone for the AP1000, and we look forward to working with utilities both in the U.S. and worldwide to build this advanced, inherently safe plant," Lipman said.
Using the AP1000, Westinghouse is leading a consortium that is bidding to build four nuclear reactors in China, a deal that could be worth $6 billion.
If the Westinghouse group wins the China bid, it's anticipated the work would preserve and create some 4,000 to 5,000 jobs in the United States, much of it in Western Pennsylvania.
Westinghouse officials recently said they had no idea when China would decide on a vendor or vendors for the plants in the cities of Sanmen and Yangjiang. Chinese officials have said the decision, originally expected by the end of 2005, would be delayed into 2006.
Areva is also bidding for the China project.
In October, the Duke Power Co., a division of Charlotte, N.C.-based Duke Energy Corp. (NYSE:DUK), contracted with Westinghouse to have two AP1000 reactors built.
The U.S. hasn't built a reactor since prior to the failure of a unit at Three Mile Island in 1979. A fire at Ukraine's Chernobyl reactor in 1986 also heightened safety concerns.
The U.S. government has said it aims to begin building new reactors around 2010.
Westinghouse is also competing to build new reactors for the United Kingdom, although Areva is said to be the front-runner.
Westinghouse, founded in 1886 in Pittsburgh by George Westinghouse, was acquired in 1998 by British government-owned BNFL from CBS Corp. for almost $1.2 billion, including $238 million in cash.
BNFL is now seeking to sell Westinghouse. Mitsubishi Heavy Industries Ltd. and Toshiba Corp. have submitted bids.
Progress Energy in Florida is also proposing to build 1 or 2 nuclear reactors in Florida.
Maybe this will get us off the Arab oil spigot.
I worked at a nuke subcontractor in the '80s. From what I saw, there's no reason it can't be safe. And there are plenty of bright people to work on decommissioning and waste fuel storage.
Well a fire occurred when the graphite burned (graphite that has been in a high neutron flux is very flammable, unlike ordinary graphite). The big issue wasn't the fires, but the fact that the core went prompt critical and released a significant fraction of its fission products to the atmosphere. This accident is fairly complicated and you really have to know a little about nuclear engineering to understand it. The short version is that physical characteristics of the core and control rods and the method that it was operating in made it very unstable and when the control rods were moved in (yes, inwards!) the reactor significantly exceeded its full power rating.
Can anybody translate this ignorant journo-speak into something that is illuminating about this plant?
"Advanced Passive 1000 nuclear plant design uses pressurized water to fire the plant."
As I recall, there was a steam "explosion" but there was a massive fire in the graphite.
I'm not sure what you are asking, but this may help. If you boil water at standard pressure, you get steam at about 212 degees F. If you put the water in a pressure cooker, you can get the temperature higher before it turns to steam. So I would think that a steam plant would use lower temperature/lower pressure.
....
Sort of, that's a good start of an answer.
Yes, the immediate cause of the spread of radiation was a steam "explosion" that blew the top off of the reactor, blew tons of plutonium and radiative by-products out into the open air (and parking lots and building roofs and across many acres. Then, to make it worse, the exposed and extremely hot graphite burned, throwing many more tons of very small particles very high into the air. Roof asphalt and other plant material also burned, but the graphite was the worse.
Because the top of the reactor was blown off by the steam explosion, the radioactive gasses (and the small radioactive particles left they they decay, were released to the atmosphere, and spread over many tens of thousands of square miles of Russia, the Ukraine, and eastern and northern Europe.
Now, why did the steam explosion happen?
First: the design was specifically optimized for creating Plutonium for warheads. Graphite moderator, poor control rod design, poor control rod controls.
Second it was built cheap: no containment, no secondary containment, no reinforced shield walls or reinforced roof: the top was simple beams and trusses and tar.
Third: The operators deliberately removed several different reactor safeguards and safety trips in order to TEST the response of the plant turbines to a simulated accident. So they DELIBERATELY created a REAL accident (running the reactor WITHOUT power to the coolant pumps!) to see what would happen to reactor coolant flow when the pumps were slowing down AFTER THE TURBINE TRIPPED. (It's sort of like trying to find out if you can change a tire on a semitruck by leaning over from a nearby car and grabbing the lug nuts.)
The immediate cause of the failure was running the reactor without coolant pumps at high power levels. The control rods had been fully withdrawn (and couldn't be re-inserted before/during the accident!) because the operators had been trying to counter a reactivity problem caused by their own previous power level changes as they set up for the test.
Great answer Robert
This may be what you are looking for:
http://www.umich.edu/~gs265/society/nuclear.htm
Discussion of pressurized water and boiling water (steam) systems, with nifty diagrams if you don't want to read the discussion. It looks like boiling water is more efficient, pressurized water may be slightly safer.
Thanks to both of you for the comprehensive explanations.
Even a pinhead such as myself now understands!
A pressurized water reactor is a fully enclosed primary system that does not allow the water to boil next to the fuel rods. Instead, the water is heated and kept under pressure to keep it in a liquid state. This primary water is then run through a heat exchanger which boils water in a secondary water loop. The steam created in the secondary loop is used to turn the turbine. This results in a less radioactive system.
Maybe should have added a sarcasm tag. I had understood that nuclear plants are "fired" by nuclear fuel, not steam.
They may not be the most "advanced" design, however, they have a long, well-documented, safety history.
Scuttlebutt I have is that the chance of US sale is small, more likely is that a Eastern European country like Bulgaria is likely to buy first.
Optimism over possible China sale is tempered by fact that a sale to the Chinese has been just around the corner for the last 25 years; and that they know full well that the Chinese will rip off the design as soon as possible and cut W out of the deal ASAP.
Did you see that other thread running about a kid who built a nuclear reactor in his mom's shed for a Merit Badge?
Well, I did say I wasn't sure what you were asking; just trying to be helpful. The quoted language did border on illiteracy.
Oh, I dunno...."hodge-podge" is how you get new ideas about doing things. I really doubt interchangability is an issue for something as large and as rare as a nuclear reactor.
Soviets tried to deny Chernobyl. The Chinese would do well by stealing our designs. Maybe they'd copy the containment buildings to go with the reactors.
Not exactly correct. Due to the positive void coefficient of the RBMK core, once the core started increasing power uncontrollably (therefore boiling off more water, adding more voids--a positive feedback cycle), the operators tried to scram the reactor. The control rods had control rod followers that displaced water. The control rod followers (tips on the end of control rods) were not neutron poisons and hence acted as a void. So for the first second or so when the reactor was scrammed, positive reactivity was added (control rods are designed to add negative reactivity to shut down the core). The scram is what destroyed the core. Normally this wouldn't be the case because there would be controls rods that weren't fully withdrawn (and if scrammed they would start adding negative reactivity immediately). The end result: BOOM!
So I guess the owner's manual in Homer's console won't start with "Congratulations on your purchase of a Fissionator 1952 Slow-Fission Reactor" anymore.
Welcome to FR, and thanks for your input, Londo.
It makes training a hell of a lot easier.
Why would the addition of a "void" by itself increase reactivity? Or was that just careless phrasing?
Oh, you mentioned graphite which has undergone neutron bombardment is more flammable. Sounds cool! Is this just an empirical observation or is the mechanism well understood?
Cheers!
Insert (groan!) your own Lewinsky / Clinton joke here.
Talk about catastrophic meltdown!
Cheers!
Well you said "AP1000 is the latest in W's designs"
Sorry, couldn't resist.
I worked for Babcock & Wilcox NPGD for about 6 years in the 70's. Left in 79 after Carter made it impossible to build new plants. Our competitors were Westinghouse and Combustion Engineering. This is good news although I don't agree on using this technology in China. Jimmah Carter can shove this where the sun doesn't shine.
In some reactors, water acts effectively as a neutron poison. For example, if a channel of water is too thick, a neutron will be unlikely to get across it before thermalizing and eventually being absorbed by non-fuel materials. If you remove some of this water, by making a bubble (to reduce the probability of a neutron interaction), you make it more likely that a neutron will get across the channel.
Reactivity (the fractional change in reactor power per effective neutron generation) is a single value for a core (when you talk about reactivity you mean that a change is occurring to the entire core). An item that causes an insertion of positive reactivity will have an effect all across the core. For example, if you create a void (an area where water is not acting as a neutron poison--a bubble or something that displaces water but is not a neutron poison as well) you will increase the power all across the core (though the power density in localized areas will vary). For this reason it is known as a positive void coefficient.
There are also cores with negative void coefficients. In these reactors, water is used as a moderator and removing it will cause an addition of negative reactivity to the core. This is also slightly linked to the temperature coefficient of reactivity. For these cores as the temperature of the moderator increases, it's density decreases making it a less effective moderator (like tiny voids between the atoms, though nobody calls it that). Thus reactor power will decrease with a negative temperature coefficient of reactivity as temperature increases--making it a very stable reactor.
Hopefully this explains why the RBMK required graphite as a moderator. This was a very brief description of a couple of reactivity coefficients, but if you are curious, you can probably find out more by reading the reactor theory DOE training manuals (they are written for people unfamiliar with reactor operations).
Graphite will start to store energy as atoms are knocked around by neutrons. Carbon atoms are knocked into higher potential energy states, which causes the graphite to become more flammable, and to bulge. In fact, there was quite a learning period for initial reactor designers who used graphite, because of the slight bulging of the graphite damaging the reactors. They were also surprised that graphite could initially catch fire. For many years reactor designers were adamant that graphite was not flammable due to their extensive studies on non neutron irradiated graphite. Then the Windscale plant caught fire and they had to learn a lot of new lessons about neutrons. Neutrons affect a lot of things. It is always important to remember that neutrons from a fission reaction can be traveling about 2-10% of the speed of light. When you pay attention to the microscopic structure of materials, neutrons can cause a lot of havoc.
RE: Chernobyl. I remember the stories of the heroism of the Russian helicopter pilots as they flew into fatal radiation zones to dump concrete on the hot reactor core. Most of these brave men eventually died due to radiation poisoning. That said and having enough knowledge of things nuclear from the service, I would prefer to live next to a modern, US designed nuclear facility, than I would to live in any large US city.
That's what I was looking for...
...err, higher electronic states or the nuclei are knocked into unstable positions within the lattice? Either could cause increased reactivity ;-)
Thanks! ...oh, and Happy New Year!
Sorry, I'm still confusticatd ;-)
If water is a moderator, how does removing it add NEGATIVE reactivity to the core?
I've bookmarked your DOE reactor theory link. Thanks!
Second it was built cheap: no containment, no secondary containment, no reinforced shield walls or reinforced roof: the top was simple beams and trusses and tar.
I guess this is the kind of thing that happens when the state considers individuals to be expendable.
If water is a moderator, how does removing it add NEGATIVE reactivity to the core?
Thermal fission is much more effective than fast fission (meaning that neutrons at low kinetic energies--thermal energies--are much more effective at causing the fission of U-235 than those at higher energies). For this reason, reactor designers place moderators in their cores. The purpose of a moderator is to slow down the neutrons before they get to the fuel so that the neutrons are at thermal energies around the fuel particles. Depending upon the the core you can use water, heavy water, graphite, helium, or other moderators. In certain cases if you were to remove part of the moderator, you are reducing the probability of thermal fission. This causes a negative fractional change in reactor power per effective neutron generation--negative reactivity.
Now your moderator is whatever you design it to be (and whatever you call it). In the RBMK the moderator is graphite. What I mean by this is that even though a material may slow down neutrons (moderate them), it isn't a moderator unless it is designed to slow them down to thermal energies *around* the fuel. The water channels in the RBMK certainly moderated (as in slowed down) neutrons, but water wasn't the moderator. The channels were too thick and neutrons had a hard time crossing them. But the graphite moderator in the core was more than enough to keep the reactor critical. For this reason, you can consider the water channels in the RBMK to be neutron poisons because their existence would cause a lower average fractional change in reactor power per effective neutron generation than without them--i.e. they are a source of negative reactivity.
I was already aware of the relation of the fission cross section to the neutrons' kinetic energy profile; my error was in assuming the water effectively reduced the neutron flux, i.e. "absorbed" the neutrons.
In other words I had the specialized definition of "moderated" incorred.
Thanks.
...and Happy New Year.
Further, they KNEW that the firefighting, concrete dumping, etc. would kill them - and they did it anyway.
Brave men indeed.
If water is a moderator, how does removing it add NEGATIVE reactivity to the core?
Another way of looking at it: If I have a thermal reactor (one that uses "slow" neutrons at "low" speeds as they hit each U235 atom) then anything I do to increase the amount of water near my fuel HELPS fission. So, adding more water increases efficiency -> more power. Cooling the water down = more dense water = more thermal neutrons = power begins to increase a little. Adding (inserting) a thermal control rod REMOVES neutrons (effectively) so it REDUCES power.
BUT, now what happens if I have a "fast (high energy) reactor that gets most of its power from "fast" (high-energy) neutrons hitting plutonium 239, not Uranium 235?
Anything that slows down a fast neutron REDUCES power. Anything that affect thermal (slow/low energy) neutrons doesn't really matter - too much. So, adding steam inside the core reduces the fast neutron slowing-down-abilty ability of the water = more power. Inserting a control rod (with a non-absorbing tip) into a fast reactor reduces the likelihood of a fast neutron getting absorbed, so as the TIP of the control rod goes into the core it actually increases power (a little.) Then, in normal situations, the rest of the rod goes further in, more fast (high energy) neutrons are absorbed and power goes down - exactly as you would expect.
In this accident, the "rest" of the rod never got down far enough to reduce power because the core was already rapidly increasing power because of the steam voids from the over temperature coolant.
Please, please tell me you mean secondary cooling water!
I've driven past the miles and miles of pipes in Slovakia, and can only hope they are tied to the secondary cooling water.
But, with leaks?
The void was there but that isn't what caused the event. The cause was because of adding additional moderator to the equation at a time when the reactor was in an unstable condition. I have a copy of a 1989 document entitled "Chernobyl Notebook," written by Gregoriy Medvedev, that explains the accident in that distinctive Russian way that's so compelling. Medvedev says On the eve of the disaster, my job was deputy chief of the Main Production Administration of USSR Minenergo for nuclear power plant construction. He was an expert on Soviet nuclear power plants and his description of the event shows it. Here's part of his description of the event:
SIUR Leonid Toptunov and unit shift chief Akimov were deep in thought, and they had something to think about. The drop in power to such low values had occurred from the level of 1,500 MW, that is, from 50 percent of capacity. The operating reactivity margin at that level was 28 rods (that is, 28 rods were inserted in the core). Recovery of the parameters was still possible.... Time passed, the reactor was being poisoned. It was clear to Toptunov that he would hardly be able to get back up to the previous power level, and even if he did manage it, the number of rods inserted in the core would have to be sharply reduced, and in that case the reactor had to be shut down immediately. So it followed.... Toptunov made the only correct decision. "I will not take it back up!" Toptunov said firmly. Akimov supported him. Both expounded their fears to Dyatlov. "What are you yapping about, you oaf?" Dyatlov attacked Toptunov. "After a drop from 80-percent capacity, it is allowed under the rules to go back up in a day, and you dropped from 50 percent! The rules do not prohibit it. If you will not take it back up, Tregub will do it...." This was now a psychological assault: Tregub, the unit's shift chief, who had turned the shift over to Akimov and had remained to see how the test would go, was standing nearby. To be sure, we do not know whether he agreed to increase the power. But Dyatlov calculated correctly: Leonid Toptunov was intimidated by the shouting, he went against his professional instinct. He was, of course, young, only 26, inexperienced. Alas, Toptunov, Toptunov....
But he was already making the estimates: "The operating reactivity margin is 28 rods.... To offset the poisoning another 5-7 rods belonging to the reserve group would have to be pulled out.... Perhaps I will get by.... If I disobey, they will fire me...." (Toptunov told about this in the Pripyat infirmary not long before he was sent off to Moscow.)
Leonid Toptunov began to increase the power, thereby signing a death warrant for himself and many of his comrades. The signatures of Dyatlov and Fomin were also clearly visible beneath that symbolic warrant. The signature of Bryukhanov and many other more highly placed comrades could also be made out....
And still, to be fair, it has to be said that the death warrant was to some degree predetermined by the very design of the RBMK. All that was needed was to bring about a certain set of circumstances in which an explosion was possible. And that was done....
But we are getting ahead of ourselves. Even then, there was still time to think better of it. But Toptunov continued to increase the reactor's power. Only at 0100 hours on 26 April 1986 did he manage to stabilize it at a level of 200 MW thermal. The poisoning of the reactor with fission products had continued, power could not be raised further because of the small operating reactivity margin - by that point, it was far below what was called for by the rules. (According to the USSR report to the IAEA, the reactivity margin was 6-8 rods, according to the statement of the dying Toptunov, who looked at the printout from the "Skala" computer 7 minutes before the explosion, it was 18 rods. There is no contradiction here. The report was written on the basis of material delivered from the unit where the accident had occurred, and something could have been lost.)
For a reactor of the RBMK type, as I have already said, the reactivity margin is 30 rods. The reactor was unmanageable because Toptunov, in avoiding the "iodine pit," had withdrawn several rods from the group of the untouchable reserve. That is, the reactor's capacity for excursion now exceeded the ability of the available safety systems to shut down the device. And still it was decided to continue the tests. The inner drive for success was too strong. The hope that the reactor would not let them down and would rescue them one more tme. The basic motivation in the behavior of personnel was the desire to complete the tests more quickly: "We will apply more pressure, and the job is done. Cheer up, lads!"
There were 24 minutes left before the explosion....
We will make an accounting of the most flagrant violations, both those contained in the program and also those committed in the process of preparing and conducting the experiment:
Everything we have enumerated took on a still more ominous coloring against the background of a number of unfavorable coefficients in the neutron physics of the RBMK reactor and the defective design of the control rods in the emergency safety system.
What we are referring to is that while the height of the core was 7 meters, the absorbing portion of the rod had a length of 5 meters, and above it and below it there was a meter of empty length. The lower end of the absorbing rod, which at full insertion extends below the core, was filled with graphite. In a design like this, the part of the control rods that first enters the reactor core is the lower graphite tip, then the empty 1-meter segment enters the core, and then only after that the absorbing part. In all, Unit 4 at the Chernobyl plant has 211 control rods. According to the data in the USSR report to IAEA, 200 rods were in the extreme upper position; according to Toptunov's testimony, 193 rods were up. The simultaneous insertion of such a number of rods into the core produces in the first instance a positive flash of reactivity, since the graphite tips are the first to enter the core (length 5 meters) and the empty sections 1 meter in length. A flash of reactivity is terrible in a stable and controllable reactor, but when adverse factors coincide, this addition can prove fatal, since an uncontrollable runaway ensues.
"Chernobyl Notebook" is a tragic but factual account. I couldn't put it down until I was done reading it. I received a copy of it soon after it was published, but I've never seen it posted anywhere on the web. It is my intention to scan it and make it available online some day.
I have to get a copy of the book to hand out to the next leftist idiots chanting about Three Mile Island to me.
Cheers!
...and Happy New Year!
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