In the US no electricity = reactor scram or emergency shutdown. After a scram a reactor will not melt down, But it is still very dangerous because of the lack of cooling you can fracture the cooling water and have a hydrogen explosion or a radioactive steam release.

 

Found this may help some..

http://www.csmonitor.com/USA/2011/0314/Meltdown-101-What-is-a-nuclear-reactor-meltdown

it states that a meltdown does not necessarily mean that there will be a large release of radioactivity.This will depend on the integrity of the primary and secondary containments. It seems that Chernobyl didnt have the Primary containment needed to stop its radiation leak..

 

Chernobyl was a disaster waiting to happen from the start, Not only did they not have two levels of containment they did not have two methods to scram the reactor. And they still decided to use it as pee wee’s play ground and experiment with it..

 

The reactors all have emergency power generation to keep the cooling systems
running in the event that external power is lost and the reactor is shut down.

The question is whether the generators can be kept supplied with fuel until either the
power comes back on line or the reactor can be deactivated (possibly by removing the
fuel rods, which may be highly radioactive after being inside the core for some time).

The Fukushima disaster (for instance) was caused by the emergency generators being
disabled along with the nuclear plant itself, causing a complete loss of cooling. In
that situation, the core will eventually melt down.

 

I am not at ALL an expert on this - but I believe that in Japan they were having a problem with the water leaking as well and the fuel rods were exposed and releasing radioactivity. I am VERY fearful of the powerplants. When Three Mile Island had its meltdown they said everything was fine, and some 30 years later they told everyone it was a full meltdown which wasn't publicised at the time. Its a very big danger for both coasts in the US.

 

My bona fides (so to speak): Worked at Yucca Mountain, have friends in the civilian nuclear industry (plant operators, nuclear engineers, experts in spent nuclear fuel). Been following the industry for 15 years. Not an expert (couldn't jump a feedwater valve unless you told me how to do it), but I consider myself as having above average knowledge - enough so to be able to understand what experts are saying when they go techno-babble.

I'll answer your questions and then provide detailed explanations below.

Short answer: Depends.
EMP - Yes, meltdown.
CME - Probably meltdown, depends on damage to plant equipment.
Standard Outside Electrical Blackout Long term - Maybe, depending on availability of diesel fuel and ability for NPP to provide its own power.
Standard Outside Electrical Blackout Short term - No, provided diesel generators are functional.

A total loss of electrical power, called a plant blackout, is one of the most serious threats that a NPP can face. Probably the only greater threat is an unexpected catastrophic failure of primary coolant machinery or piping or significant major component malfunction or failure.

You have to remember that NPPs have a series of redundant features. For your typical Pressurized Water Reactor (PWR), you have outside electrical power, emergency diesel generators, and finally battery power. I understand, through conversations with plant operators and nuclear experts, that if there is enough time available, the switchgears between the electric yard and turbine can be connected, allowing a reactor to essentially provide it's own power.

Further, you have to remember that when it comes to a meltdown, we are concerned about two different systems. The first is the power generation system (the reactor), the second is the spent fuel pool (used fuel storage). The two systems are fundamentally different, with different containment systems, redundancies, and strategies for dealing with a plant blackout.

Let's look at the power generation system first.

First, I need to point out that there are typically three levels of building containment in a power generation system. First, you have the Reactor Pressure Vessel. This is the actual vessel that houses the components where the nuclear reaction takes place. Second, you have a steel containment building. This surrounds the Reactor Pressure Vessel, Steam Generators, and any stuff that come into contact with nuclear materials, including coolant. Third, outside of the steel containment, you have a concrete containment. The steel and concrete containment structures are referred to as Primary Containment.

What a plant blackout does is lead to a Loss of Cooling Accident (LOCA). Simply put, coolant is needed for both the reactor and for the spent fuel pools. Reactors create a tremendous amount of heat - that's what they're designed to do. Essentially, a nuclear reactor is a way to boil water, which turns a turbine, which turns a generator, which produces power. That's it.

Without coolant, the reactor overheats, and the fuel assemblies and reactor guts melt. This creates something called corium - think of corium as radioactive lava. It's a molten mix of nuclear fuel, metal (reactor guts), and some other things that melt when the reactor gets too hot. Eventually, the corium pools at the bottom of the Reactor Pressure Vessel (RPV) (which is the steel can that contains the reactor - like how a can contains your soda), and it may melt through (Chernobyl), or it may not (Three Mile Island).

If the corium does melt through the RPV, it usually drops into a containment pit (also called a Core Catch), which is designed to prevent the corium from getting outside of primary containment. I can get into the details if you want to, but it's really not relevant to this post.

The other danger is that gasses are created during the process of a nuclear meltdown. If the RPV or other component of the primary coolant loop is compromised, then these gasses can vent into Primary Containment. While PC is designed against an explosion blowing it out, there is a chance that PC could be compromised.

If outside power is off, then the plant can run off of diesel generators. If the diesel generators are unavailable, then batteries provide a limited amount of power. When the batteries run out, then passive cooling systems attempt to keep the damage to a minimum.

I've omitted a whole bunch of things in the above explanation. Emergency Core Cooling Systems, Passive Safety, Low Pressure Coolant Injection Systems, High Pressure Coolant Injection Systems, Depressurization Systems, Core Sprays, and Isolated Cooling Systems. I can get into that if you want - but it pertains more to reactor design than it does to this situation.

That's the power generation side in a nutshell.

Onto the spent fuel pools.

The spent fuel pools are essentially gigantic swimming pools (well, they look like swimming pools - you wouldn't want to swim in them unless you had a death wish) where used fuel assemblies are stored. They are stored there for two reasons. First, used fuel assemblies are incredibly hot and continue to generate heat even after they are removed from the reactor. This is referred to as Decay Heat. Second, you need a lot of shielding between you and the fuel assemblies - water acts as a shielding for this purpose. Thus the water serves two purposes - it cools the fuel and it's a radioactive shield.

In a plant blackout, what happens is that the water that is lost due to evaporation is not replaced, and the water is no longer circulated mechanically (there is some passive water circulation, but I won't get into that). The spent fuel heats up the water (generally - more on the exceptions in a moment), eventually causing it to boil off. The water level drops, the fuel becomes exposed, and it eventually either catches fire and/or melts down. In a very extreme case, you may have an uncontrolled nuclear reaction occur (note - this is not similar to a nuclear bomb).

Some, but not most, spent fuel pools are designed to radiate enough heat that you really don't need to put water in them. Once it goes in, that's enough, and there are passive systems to replenish the water supply. Most, to my knowledge, are not, because we were supposed to have a place to dump this fuel by now (Yucca Mountain), and we don't, so we've been forcing NPPs to keep spent fuel on site.

The spent fuel takes anywhere from 2 to 7 years to cool adequately. For safety reasons, you'll never hear a nuclear expert say anything less than 5 years, but I've been told that they could do it in 2 if they really had to. After the fuel has spent the appropriate amount of time in the pool, they move it to a dry casket and store it outside.

Most spent fuel pools - but not all - are stored in containment buildings similar to Primary Containment found around reactors.

Hope this makes sense.

Let me know if you have any questions.

 

Hopefully, everyone understands the time frames we are talking about here.

Reactors are not like light switches. Even if you SCRAM the reactor, it takes a very long time to cool the system down from operating temperature- days to weeks in most cases. And if there was a reactor incident the heating problem is magnified by the time the reactor was in runaway.
That very long cool down is where a lot of the dangers come in, because you have to keep it cool to prevent or reduce meltdown, to stop generating corium, to cool the melted mass, etc, etc. In Japan they couldn't move water, the backup generator fuel tanks were contaminated with seawater, so they wouldn't run. The containment pools ran dry, hydrogen gas was generated by the overheated rods and got hot enough to explode, which ruptured the containment and exposed the rods to the air... and it spins out of control once the rods are exposed.
At three mile island, primary containment could take a hydrogen explosion, but most wastefuel storage is ...flimsier.

TRM put his finger on the real danger - waste storage in the US is a joke and a disaster waiting to happen. Yucca Flats was the solution, but no one had the backbone to demand it be put into service whether NV liked it or not. The current system is very, very overcrowded and getting more dangerous every day,

 

There are currently plans underway at all USA plants to implement static cooling loops that won't require electricity to keep the reactor and the fuel pools cool until they reach a point where natural cooling (air, water or whatever) will be enough. Now how long it will take to implement these plans is anyones guess.

 

But aren't those loops only for the primary coolant loops, not for the secondary or tertiary?

 

One more thing to think about, every single bit of "spent fuel" that has EVER been generated, and each reactor generates about 25 tons per year, is currently being stored "onsite". The place to store the spent fuel safely was never built. Most reactors have about 75 tons of fuel in them and another 75 to 150 TONS of spent fuel sitting in a big bathtub. That fuel must be kept cool for YEARS or it will melt down, and do you know why?
Because it's not "spent"
They call it spent because the zirconium cladding that encloses the fuel pellets becomes less transparent to the neutrons over time and the rods won't react with the other rods correctly. The fuel isn't spent at all, it's really just sort of less productive. The plan was to reprocess the old rods and make new ones, but it has been cheaper to just make new fuel for the last 40 years.
I thought that I was safe here in northern CA (except for fallout from Fukushima)because our only NPP, Rancho Leako was shut down by popular demand several years ago.
But guess what? I did some digging and wouldn't you know it, they removed the reactors and the other stuff but every bit of the "spent fuel" is still there being kept cool in a big bathtub.
People need to do a little research on this subject before it's too late. We are being lied to about almost everything about nuclear energy.

 

Because it's not "spent"
They call it spent because the zirconium cladding that encloses the fuel pellets becomes less transparent to the neutrons over time and the rods won't react with the other rods correctly. The fuel isn't spent at all, it's really just sort of less productive.

It has nothing to do with the clad. As the Uranium undergoes fission it becomes 2 (or more) atoms of something else. Once the concentation of Uranium drops below a certain point you can't cause criticallity because there are too many non-fuel atoms absorbing the neutrons. Reprocessing purifies the Uranium back to a level where it will support a reaction.

We don't do reprocessing because all the tree huggers didn't or couldn't do the math. The same reason they prevented a central place to store waste.

Once the fission products in the spent fuel decay to a certain point the fuel can be repackaged into dry storage, but this may take months to years depending on the fuel. Once it is in dry pack it can be stored in perpetuity safely.

 

According to my research, the fuel becomes unusable due to the buildup of contaminants and the inability of the fuel to radiate it's heat (sort of like neutrons) causing the center of the fuel pellets to melt down.
This is because of the reaction of the fuel with the Zirconium cladding.

Here is some info from Wiki on the subject. I found this at http://en.wikipedia.org/wiki/Nuclear_fuel_cycle

Fuel cladding interactions

The study of the nuclear fuel cycle includes the study of the behaviour of nuclear materials both under normal conditions and under accident conditions. For example, there has been much work on how uranium dioxide based fuel interacts with the zirconium alloy tubing used to cover it. During use, the fuel swells due to thermal expansion and then starts to react with the surface of the zirconium alloy, forming a new layer which contains both fuel and zirconium (from the cladding). Then, on the fuel side of this mixed layer, there is a layer of fuel which has a higher caesium to uranium ratio than most of the fuel. This is because xenon isotopes are formed as fission products that diffuse out of the lattice of the fuel into voids such as the narrow gap between the fuel and the cladding. After diffusing into these voids, it decays to caesium isotopes. Because of the thermal gradient which exists in the fuel during use, the volatile fission products tend to be driven from the centre of the pellet to the rim area.[7] Below is a graph of the temperature of uranium metal, uranium nitride and uranium dioxide as a function of distance from the centre of a 20 mm diameter pellet with a rim temperature of 200 oC. The uranium dioxide (because of its poor thermal conductivity) will overheat at the centre of the pellet, while the other more thermally conductive forms of uranium remain below their melting points.

And another thing,
It's hard to believe that the "tree huggers" forced us to store thousands of tons of radioactive waste in our back yard instead of finding a safer place to store it.

 

And another thing,
It's hard to believe that the "tree huggers" forced us to store thousands of tons of radioactive waste in our back yard instead of finding a safer place to store it.

And yet, that's how it went down. The concerns at Yucca Flats were over the gigantic amount of waste that was scheduled to go there, the possibility of a major seismic rupturing containers and contaminating groundwater, or a reactivity-generated event or fire venting to the surface and generating a radiation plume. These were valid concerns that were carefully addressed. Repeatedly, and at great expense. They wouldn't let it go, despite the massive dangers of the current stop-gap system. Then NIMBY occurred and it all went sideways. Congress gave up instead of growing a pair and demanding the site be used. Billions of dollars dropped down a rat hole.

 

What cracks me up is we threw conniptions over Yucca Flats, which is dry, in a mountain, and very, very, stable. And we decided to not use it.

But we throw high-level transuranic waste into WIPP, which is nothing more than a salt mine located very close to Carlsbad caverns. The region has massive pools of Brine under pressure all through it, is near New Madrid, and has the worst waste in the country there. Brine is corrosive as hell. The fossil water reservoirs of the mid west and the Mississippi river are not that far away. I can hardly think of a place I would refuse over that one.

 

OK what happens if the dollar melts down? Will people stay on the job when they have families to take care of, but no food or paycheck? Is that when FEMA protects us?

 

OK maybe im just stupid but dont nuclear reactors produce power now days how would they ever LOSE power

 

In a CME or EMP the support electrical systems would fry or the transformers going out and in would fry. This would cause an automatic scram. Damage to control systems would prevent re-start, thus leaving the reactor in a situation where it still was producing a great deal of decay heat but had no means to remove it unless a static cooling loop is available.

If you look at the diagram above you have the reactor loop which carries the heat to the secondary loop which produces the steam to turn a turbine that turns a generator to make electricity, then the steam is cooled by a third cooling loop. All of those pumps and valves and pressure controllers and instruments are susceptible to damage during a CME or EMP event. You have to have a great deal of delicate circuitry in the various controllers and monitors that keep everything going.

 

I

If you look at the diagram above you have the reactor loop which carries the heat to the secondary loop which produces the steam to turn a turbine that turns a generator to make electricity, then the steam is cooled by a third cooling loop. All of those pumps and valves and pressure controllers and instruments are susceptible to damage during a CME or EMP event. You have to have a great deal of delicate circuitry in the various controllers and monitors that keep everything going.

This is a clearer schematic that references what Mike is talking about. Easier to follow.

 

There was a old design for reactors that had a vessel under the reactor vessel full of lead blocks in case the reactor melted down.
The lead blocks would dilute the corium and stop the neutron reaction plus contain much of the radioactivity.

These pits were used at the navy test reactors in Idaho where they did special tests that in extreme conditions might cause a melt down.

The expense of adding this safeguard to any new reactors would be low and adding any extra levels of protection would be worth it.

There is also a group working on a scram generator system that allows the reactor to power its own backup generator system.

This system uses a binary cycle power plant that runs off hot water instead of steam and can supply power from the reactor to to cool the reactor that is in scram down to a cold state.
http://en.wikipedia.org/wiki/Binary_cycle

The reactors would still have diesel backups but this would add a extra level protection.

There is another group that is looking at reactors that never go full critical and run completely on hot water instead of the steam cycle. They also use the binary cycle power plant.

There is even a chance they can use spent fuel to make power during the early part of its storage to run the spent fuel cooling facility and have extra power from this to sell.

As for hydrogen explosions in US reactors the problem is a lot less likely because US reactors have passive hydrogen recombiners something japan never added to there reactors after they were invented.

Every accident has made things safer for the remaining power plants.

 

For a good background on nuclear energy and its effects I recommend "From Hiroshima to the Moon". History and useful info!

 

Yes, that is why Fukushima melted down. They lost power and could not keep the fuel rods from heating up. Or something like that.

Cooling towers can't function without power. Think about it?

 

Which is why they are implementing passive cooling that works without electric power.

 

I'm no scientist

I'm no scientist but I do have 7 years of college and I know when I see a serious problem. There have been to many accidents in my lifetime to not think about some kind of nuclear power plant catastrophe. I live less than 20 miles from two plants and my friend has just retired from one of them. After what he tells me about the power plant my wife and I have made evacuation plans to get our children out in case of an accident. I remember what I learned in college. A nuclear reaction is only a theory and has never been proven scientifically. I don't want so called experts telling me everything is ok and not to worry.

 

"A nuclear reaction is only a theory and has never been proven scientifically."

Only proven in that they shoot a neutron at Uranium (fact), it splits (fact),more nuetrons are created from the reaction (fact), which go on to cause other fission reactions (fact). Other that that it is all theory.

You were correct when you said you weren't a scientist, let's just leave it at that.

 

+1 quoted for truth.

 

Quote:
There is only one "IF". If the country collapses from "X" we will have no electricity. No electricity WILL cause the nuclear power plants to meltdown. That is a fact.


The Nuclear plants have a 4-8 hour battery backup system and redundant backup generators. If we had a similar event like Fukushima where the grid went down, the backup generators failed "and or" the electricity was not restored within 1-2 weeks. Yes we could have an almost identical situation as Fukushima. Are our Reactors set to higher standards? Not really as 23 of our Reactors are the same GE Mark I Reactors as at Fukushima.

The risk of life is actually VERY low in a full meltdown as the event is slow so people have time to evacuate. The permanent evacuation zone could be as large as a 50 mile radius in a full meltdown with damaged Spent fuel pools. Worst case scenario would be just like Fukushima.

 

Actually ours are at a higher mark since all suggested upgrades have been performed at our plants while Japan didn't apply them to theirs. Also, had there not been a tsunami along with the earthquake the Japan incident wouldn't have happened. It was both a record earthquake and the record tsunami that caused the accident. It was not just a loss of power, it was the tsunami that eliminated the emergency generator that caused the meltdowns to occur. Could it occur here? Yes, if the same combination of events happened. Now, what are the chances of the same combination of events happening? Very, very low by anyones approximation.

Once the passive cooling systems are added to the USA plants the chances of even a full-on EMC attack causing a meltdown are small.

 

This is the same kind of BS I herd from the so called experts about our plants when three mile island occurred. It's always there's nothing to worry about and when something does go wrong everyone jumps up and points their finger at everyone else. I don't need to hear any more BS.

 

yer gonna luv *this*...

IEEE (who are very much to be taken seriously) warns of "hundreds of Fukushimas"
in the event of a CME event:

http://spectrum.ieee.org/energy/the-smarter-grid/a-perfect-storm-of-planetary-proportions/0/hundreds-of-fukushimas

 

IEEE (who are very much to be taken seriously) warns of "hundreds of Fukushimas"
in the event of a CME event:

http://spectrum.ieee.org/energy/the-smarter-grid/a-perfect-storm-of-planetary-proportions/0/hundreds-of-fukushimas

Which is why plants in the USA are implementing passive cooling systems that don't require electricty.

 

"Are implementing" are the critical words, yes, if it happened right now we would be screwed.

 

Whew...I'm glad the wind never blows. ...Oh wait..I think it does..!


First I thought, good. No reactors here in New Mexico. Then I remembered there are governmental reactors in Los Alamos. Oh well...

I believe I read about a reactor built almost on top of the San Andreas fault in California.

 

When you are discussing passive cooling systems. Don't confuse the new designs that they are working on with actual systems that are installed in the power plants.
Remember, "implementing" can mean a lot of things.

 

There seems to be a need for some actual facts here.
Nuke plants in the USA have several backup cooling systems.
I have seen, 2 diesel gens, multiple retention ponds,
off site power, and access to the cooling water in the canal.
Are your preps that good?
In addition, there are manually operated Boron systems that will KILL a reactor
nuclear reaction.
I have personally tossed a engineer out of a nuke drywell
that didn't know where the system was located.

kctgb: You will not hear the truth about that plant, although I have NOT been there, I have 10+ years working on the same design plant. Those reactors are FUKed, so to say.
US workers wont tell you whats going on there.
Dose rates would be through the roof, and the NRC frowns on going over the dose limits
for workers. There are GE techs that travel the world doing some hard, dangerous jobs in the plants. They are willing to max out their dose rates in the USA, then travel to other countries to get more. Its all about the money.
As far as TMI goes, it was a non event. Get over it with TMI, there was NO release

 

There seems to be a need for some actual facts here.
Nuke plants in the USA have several backup cooling systems.
I have seen, 2 diesel gens, multiple retention ponds,
off site power, and access to the cooling water in the canal.
Are your preps that good?
In addition, there are manually operated Boron systems that will KILL a reactor
nuclear reaction.

Didn't Fukushima have these backups? How are ours different?