Can a nuke power plant just blow up?

[alancj]

Ok, I was watching the movie "Resident Evil: The Apocalypse" the other day. The big evil "Umbrella Corporation" nukes a city to kill the T virus (which is what makes the people turn into zombies ) The cover up for the city getting vaporized is too just say that the local nuclear power plant had a meltdown. I laughed because I don't even think it’s possible for a power plant to just detonate like that. Don't you need highly specific conditions in order to get that kind of a nuclear explosion; something that purposely cannot be met in a nuclear reactor?

-Alan

 

[Grogs]

It took a lot of smart people many years to make the first nuclear bombs. It's not something that just happens. Probably the worst-case scenario for a reactor would be a steam-explosion, like Chernobyl. It was enough to blow chunks of the reactor core through the roof of the reactor building. Unlike Chernobyl, all commercial reactors in the US have a large steel-reinforced concrete containment building around the reactor core meant to contain such an explosion, so even that type of scenario is very unlikely.

 

[Pengwuino]

I think he meant the real whole nuclear explosion type deal which is impossible. You'd need to introduce a tremendous number of neutrons very very quickly to create an explosion I believe.

 

[alancj]

I think he meant the real whole nuclear explosion type deal which is impossible. You'd need to introduce a tremendous number of neutrons very very quickly to create an explosion I believe.

Exactly what I thought...

 

[Astronuc]

I think he meant the real whole nuclear explosion type deal which is impossible. You'd need to introduce a tremendous number of neutrons very very quickly to create an explosion I believe.

One could have a prompt critical event, but not like a nuclear warhead. The critical mass in a warhead is nearly pure fissile material and then it is compressed (density increased above normal).

Likely in a nuclear reactor, the prompt event could initiate a pressure pulse which, if strong enough, could cause piping to rupture, or perhaps the pressure vessel to rupture, but then the coolant (assuming water) would flash to steam and one would have a thermal/steam explosion, not a nuclear explosion.

However, introducing sufficient reactivity, by say removing all control rods rapidly is essentially physically impossible.

 

[Wailing Fungus]

It is impossible to have a nuclear explosion.

The uranium in nuclear reactors a mixture of U235 and U238, where U235 is only a small percentage, in order to control the reaction.

 

[Facial]

You can have a steam explosion.

But a nuclear one? No. The uranium used in reactors is not enriched enough.

 

[alancj]

Well, I guess I shouldn't expect too much from a movie like that. I hate plot holes though; and I think that that movie had some to spare...

 

[PerennialII]

Well, I guess I shouldn't expect too much from a movie like that. I hate plot holes though; and I think that that movie had some to spare...

... perhaps they wanted to explain the casualties and not the event itself, it's not like people are lining up to see the results anyways .

 

[alancj]

... perhaps they wanted to explain the casualties and not the event itself, it's not like people are lining up to see the results anyways .

No, it was supposed to cover up the nuclear bomb that they drooped on the city. Which is basically what the characters said in the movie, "they’ll nuke Raccoon City with a 5 kiloton bomb and say it was a meltdown at the nuclear power plant."

Pretty freaking dumb…

-Alan

 

[Pengwuino]

No, it was supposed to cover up the nuclear bomb that they drooped on the city. Which is basically what the characters said in the movie, "they’ll nuke Raccoon City with a 5 kiloton bomb and say it was a meltdown at the nuclear power plant."
-Alan

Yah, no one except 99% of hte general public would believe that crap.

On a related note... some science show (on a reputable channel!) was talking about fusion experiments such as ITER. They were saying that there was a possibility that a fusion test reactor like ITER or the NIF could blow up when started in a small thermonuclear explosion. They can't be using that much fuel could they?

 

[Morbius]

On a related note... some science show (on a reputable channel!) was talking about fusion experiments such as ITER. They were saying that there was a possibility that a fusion test reactor like ITER or the NIF could blow up when started in a small thermonuclear explosion. They can't be using that much fuel could they?

Pengwuino,

With respect to NIF - that sounds like the same fear mongering that the local anti-nuclear
group "Tri-Valley CARES" has been spreading.

For example, LLNL recently enhanced its security by adding Dillon Aero M134 Gatling
guns to the Lab Protective Force's arsenal of weapons:

www.llnl.gov/pao/com/2006/spring_discover_llnl.pdf[/URL]

The M134 fires depleted uranium rounds. The anti-nukes leafeted the houses near
the Lab, including mine; stating that if they shoot those guns then my house will be
radioactive for 1,000 years [ where they got that number, I don't know - it has
nothing to do with the 4.5 Billion year half-life of the U-238 in depleted uranium] and
that my house value is now zero. I won't be able to sell my house.

The anti-nukes are so self-righteous that they believe they can tell any type of lie
they want in order to further their cause.

Dr. Gregory Greenman
Physicist

 

[Grogs]

stating that if they shoot those guns then my house will be radioactive for 1,000 years [ where they got that number, I don't know - it has nothing to do with the 4.5 Billion year half-life of the U-238 in depleted uranium]

A lot of those folks don't do big numbers. I guess anything over 1000 is all the same to them. Too bad the ones protesting Yucca Mountain can handle the large numbers better.

One of the saddest 'facts' I ever saw on one of those 'DU is destroying the world' type webpages was this: "IN A SINGLE GRAM OF URANIUM-238, THERE ARE MORE THAN 12,000 RADIOACTIVE DECAYS PER SECOND!" (not sure about the number of exclamation points.) It was sad because the number is correct, and the person who sat down and computed the specific activity surely knew 12,400 decays per second is miniscule. A gram of Technetium-99m, which is regularly injected into people for diagnostic tests, has a specific activity of ~2x10¹⁷ decays per second. They just chose to portray the facts in a way that would scare uneducated people.

 

[Morbius]

They just chose to portray the facts in a way that would scare uneducated people.

Grogs,

Exactly! Nuclear technology is not something that is taught as part of the "general
education" one gets in K-12 schooling. Since people don't know anything about the
technology - it is easy to scare them by telling them it does something it doesn't -
like blow up.

Dr. Gregory Greenman
Physicist

 

[Vincent Vega]

In the movie "K-19: The Widowmaker" a Russian nuclear submarine reactor malfunctions and (in the movie) the crew was worried about a minor explosion triggering warheads aboard. I was always under the impression for the warheads to work they must go through specific steps.( like a gun-triggered fission bomb for example)

 

[NateTG]

The hard part is getting the fissible material. The gun-barrel designs can be quite simple - they can be triggered by a single explosive charge. (Implosion designs tend to be more complicated.)

Generally, nuclear plants are designed to fail in a less catastrophic fashion.

 

[Morbius]

In the movie "K-19: The Widowmaker" a Russian nuclear submarine reactor malfunctions and (in the movie) the crew was worried about a minor explosion triggering warheads aboard. I was always under the impression for the warheads to work they must go through specific steps.( like a gun-triggered fission bomb for example)

Vincent,

Yes - at least the USA's weapons, and I assume the Soviet weapons, have "locks" on
them. Some are known as PALs - "Permissive Action Links".

The weapons are locked so they can't be detonated in an accident, and a rogue
military officer can't launch a nuke without orders. For example, on USA Trident subs
the "Captain's missile key" is not in the possession of the boat's skipper. It is locked
in a safe. Nobody on board has the combo to the safe. The combo to the safe is
received as part of the order to launch. For more on this see the book "Big Red":

https://www.amazon.com/gp/product/0060194847/?tag=pfamazon01-20

Dr. Gregory Greenman
Physicist

 

[Morbius]

The hard part is getting the fissible material. The gun-barrel designs can be quite simple - they can be triggered by a single explosive charge. (Implosion designs tend to be more complicated.)

Generally, nuclear plants are designed to fail in a less catastrophic fashion.

Nate,

It's not quite as simple as you make it out to be.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

Generally, nuclear plants are designed to fail in a less catastrophic fashion.

Generally, nuclear plants are designed NOT to fail!

 

[flamesniper]

lol I love the RE movies, I don't care what people say about them!
Anywho, nuclear reactors employ moderators (like heavy water, carbon, etc) that absorb the neutrons from the fuel (Uranium or Plutonium). By absorbing neutrons, a chain reaction cannot occur causing a powerplant to explode. As previously and correctly stated in earlier posts, the fuel is not nearly enriched enough (you need it to be about 80-odd% enrichment, I think).
To my understanding, one of the factors leading to Chernobyl was because one of the technicians pulled out the moderator ---> chain reaction --->boom (well, implosion).
[Feel free to correct me, if I got anything absurdly wrong]
I suppose it just goes to show how misconceptions are purveyed in a society that is very nuclear-illiterate.

 

[theCandyman]

I do not think enrichment in reactors is so high. I recall it is closer to 5~6% w/o U-235. Also, the way I understand it, the moderator in Chernobyl was not removed, but instead because of the positive void coefficent of the reactor, it ceased moderating as well as it should have (basically the density of the moderator decreased, and the cross section of the moderator along with it).

 

[Astronuc]

The maximum allowable U-235 enrichment in commercial nuclear fuel is 5%, but that usually means 4.95% to allow for uncertainty. This limit is generally applied world-wide in the nuclear power industry.

In Chernobyl, control elements were being moved with protection systems disabled, since I believe the maneuver should have activated the protection systems. Anyway, the power increased too rapidly to respond, and the coolant (pressurized water) changed phase from liquid to steam, which in the graphite-moderated RBMK added more reactivity to the reactor - which led to a rapid power excursion and steam explosion.

 

[Morbius]

The maximum allowable U-235 enrichment in commercial nuclear fuel is 5%, but that usually means 4.95% to allow for uncertainty. This limit is generally applied world-wide in the nuclear power industry.

Small research reactors which used to run on fuel with high enrichment are now mostly
limited to 20%. The enrichment used by naval warships is still high.

In Chernobyl, control elements were being moved with protection systems disabled, since I believe the maneuver should have activated the protection systems. Anyway, the power increased too rapidly to respond, and the coolant (pressurized water) changed phase from liquid to steam, which in the graphite-moderated RBMK added more reactivity to the reactor - which led to a rapid power excursion and steam explosion.

At Chernobyl, the operators were planning an experiment with the reactor when it
was going to shutdown for an outage. They lowered the power of the reactor in
preparation for doing the experiment. However, before they began the experiment,
the electric load controller in Kiev called them and asked that they remain online
for a few hours more. The plant stayed online for about another 12 hours at this
lowered power level. It was then that the operators began their previously planned
experiment.

However, whenever you shutdown or lower the power level in a reactor, there is a
temporary buildup of Xenon-135, which is the radioactive daughter product of the
fission fragment Iodine-135. The reactor undergoes what is called a "Xenon
transient" because Xenon-135 is THE world champion neutron absorber! If
memory serves, it has a thermal absorption cross-section of 6 Million barns.

At the time of the accident, about 12 hours after power was reduced; the Chernobyl
reactor was right in the middle of the Xenon transient - right when Xenon concentration
peaked. The Xenon "poisons" the reactor, and makes it difficult to control and stay
in operation.

In fact, in order to keep the reactor working - the operators had to completely remove
ALL control rods from the reactor - in violation of approved operating procedures.
With the reactor in this VERY unstable state, with Xenon poisoning, and control
rods withdrawn - the operators began their experiment. The experiment required that
the operators disable the reactor safety systems, as they would prevent the
experiment from being conducted.

Nobody ever planned on doing this experiment in the middle of a Xenon transient
with all control rods removed, and nobody knew what the effects would be!
With the safety systems turned off - the operators began the experiment with the
very unstable reactor and... the rest is history.

A totally preventable accident - if only people would THINK about what they were
doing. However, in an oppressive society like the USSR - you did as you were told.

Dr. Gregory Greenman
Physicist

 

[theCandyman]

Wow, my professor just covered Xe-135 poisoning this past week. Was there much known about poisoning at the time of the accident?

 

[Astronuc]

Wow, my professor just covered Xe-135 poisoning this past week. Was there much known about poisoning at the time of the accident?

It has been well known for years before the Chernobyl accident since the 1950's. I believe it was Enrico Fermi who figured it out.

Here is a useful resource on nuclear power - http://book.nc.chalmers.se/KAPITEL/CH19NY3.PDF

 

[Morbius]

It has been well known for years before the Chernobyl accident since the 1950's. I believe it was Enrico Fermi who figured it out.

Astronuc,

Actually, it was Eugene Wigner.

They noted this the first time they powered up the big production reactors
at Hanford during WWII - about September 1944. Previous to this, all the
reactors like Fermi's Chicago pile, and X10 at Oak Ridge were pretty low
power.

They shutdown one the Hanford reactors [B reactor?], and a short time later
tried to restart it - but it wouldn't restart. Everybody on the project was baffled
and upset. After all, they had just completed these reactors, and the Manhattan
Project and the War effort were counting on them, and they "broke" the reactor.

Eugene Wigner told them to wait a day - and then try to restart. Sure
enough, the reactor restarted just as Eugene Wigner said it would.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

Thanks Morbius for correcting my faulty memory.

http://nobelprize.org/physics/laureates/1963/wigner-bio.html
http://nobelprize.org/physics/laureates/1963/index.html

He did a lot of work on resonances, as in Breit-Wigner resonance.

I remember the story of the Hanford reactor, and the someone (Wigner) told them to wait. As I understand it, he flew out there and when he arrived, he has developed the theory.

 

[Morbius]

I remember the story of the Hanford reactor, and the someone (Wigner) told them to wait. As I understand it, he flew out there and when he arrived, he has developed the theory.

Astronuc,

Here's another link that covers Wigner and Xenon poisoning courtesy of
Physics Today:

http://www.aip.org/pt/vol-55/iss-10/p42.html

From this it appears Wheeler, Fermi, and Babcock figured it out.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

Morbius, thanks for that. I heard the story from a professor who new some of those guys. The details were a little fuzzy after 35 years.

 

[Morbius]

Morbius, thanks for that. I heard the story from a professor who new some of those guys. The details were a little fuzzy after 35 years.

Astronuc,

Same here - I heard my story from Professor Alan F. Henry.

Dr. Gregory Greenman
Physicist

 

[Homer Simpson]

Have you ever heard of the Graphite tipped absorbers used at Chernobyl?? that seemed a bit of design gaffaw. Upon pulling out the absorbers to far in order to remain critical, they eventually dropped the absorbers to trip the reactor. The thing is that the graphite displaced water which led to yet another positive reactivity insertion (along with the voiding)

 

[Morbius]

Have you ever heard of the Graphite tipped absorbers used at Chernobyl?? that seemed a bit of design gaffaw. Upon pulling out the absorbers to far in order to remain critical, they eventually dropped the absorbers to trip the reactor. The thing is that the graphite displaced water which led to yet another positive reactivity insertion (along with the voiding)

Homer,

Yes - I have heard that.

Remember, the Chernobyl RBMK reactor is NOT SUPPOSED to be run with the rods
completely out for exactly the reason you point out.

By pulling the rods completely out, when the operators called for a SCRAM when
the reactor power spiked, the very first part of the rod's insertion was actually
inserting moderator - not neutron absorber.

So the first several inches of rod insertion is actually a reactivity insertion not a
neutron poison insertion. So with the rods completely out - you have to ADD
MORE reactivity to the reactor before you can DECREASE reactivity.

Yes - that's yet another BAD design aspect of the Soviet RBMK reactor.

It's another thing that I point to when the anti-nukes cite Chernobyl as a reason
for foregoing nuclear power in the USA. They always say, "Look what happened
at Chernobyl - we shouldn't build any more nuclear power plants". The problem is -
nobody is talking about building any more RBMK reactors.

Dr. Gregory Greenman
Physicist

 

[Grogs]

Homer,

Yes - I have heard that.

Remember, the Chernobyl RBMK reactor is NOT SUPPOSED to be run with the rods
completely out for exactly the reason you point out.

By pulling the rods completely out, when the operators called for a SCRAM when
the reactor power spiked, the very first part of the rod's insertion was actually
inserting moderator - not neutron absorber.

So the first several inches of rod insertion is actually a reactivity insertion not a
neutron poison insertion. So with the rods completely out - you have to ADD
MORE reactivity to the reactor before you can DECREASE reactivity.

Yes - that's yet another BAD design aspect of the Soviet RBMK reactor.

Morbius:

I'm curious. It couldn't be an accident they put one of the best moderating materials known to man on the end of the control rods. Do you have any idea what the intended purpose of the tips was? Some sort of oscillation dampening perhaps?

 

[Morbius]

I'm curious. It couldn't be an accident they put one of the best moderating materials known to man on the end of the control rods. Do you have any idea what the intended purpose of the tips was? Some sort of oscillation dampening perhaps?

Grogs,

I don't really know why they did that - perhaps to add reactivity when the rods were out?

When you look at the Soviet designs - they seem to discount the effect of their design
choices on accidents. In other words, they REALLY COUNTED ON not having any
accidents. So if a design aspect made an accident scenario worse - it didn't matter
to them because there weren't going to be any accidents.

That was just the Soviet philosophy - they didn't have accidents. If something went
wrong - it was sabotage! The Soviets were always executing or imprisoning
people after accidents - because they didn't believe in accidents - they had sabotage.

As long as they had loyal operators that wouldn't sabotage the plant - then nothing
would happen - there would be no accidents - so no use planning for them.

That appears to be their philosophy - completely foreign to us.

Dr. Gregory Greenman
Physicist

 

[Homer Simpson]

Do you have any idea what the intended purpose of the tips was?

The Shutoff rods were also used as Control Rods. Since these rods were cooled by light water in a tube, the boron rod (a good absorber) would displace light water (also a good absorber) so the difference in reactivity would not be that great. The graphite was called a 'displacer'. It made the effect of rod movement greater, because as the boron rod moves down it displaces graphite, not light water. In the fully inserted position, the graphite section was out of core on the bottom. When the rods were fully out of core the control rod tubes were part graphite at the top and light water at the bottom.

During the accident, when the rods began to move in the bottom of the core became very supercritical.

 

[Morbius]

The Shutoff rods were also used as Control Rods.

Homer,

That's true in an US-designed reactors as well.

Since these rods were cooled by light water in a tube, the boron rod (a good absorber) would displace light water (also a good absorber)

Light water is NOT a good absorber relative to Boron.

so the difference in reactivity would not be that great. The graphite was called a 'displacer'. It made the effect of rod movement greater, because as the boron rod moves down it displaces graphite, not light water.

Only to the extent that the graphite ADDS reactivity - that the subsequent Boron
counteracts. That is relative to an LWR, this increase in control rod effect merely
serves to cancel the positive contribution of the graphite.

In the fully inserted position, the graphite section was out of core on the bottom. When the rods were fully out of core the control rod tubes were part graphite at the top and light water at the bottom.

During the accident, when the rods began to move in the bottom of the core became very supercritical.

Regardless of the above; the RBMK control system requires that when an
emergency shutdown is needed - the rods have to ADD reactivity before they can
DECREASE reactivity.

All in all - it's a pretty dumb thing to do from a safety standpoint - as they found out
the hard way.

Dr. Gregory Greenman
Physicist

 

[Homer Simpson]

Light water is NOT a good absorber relative to Boron.

Relative to graphite it is.

Only to the extent that the graphite ADDS reactivity - that the subsequent Boron counteracts. That is relative to an LWR, this increase in control rod effect merely serves to cancel the positive contribution of the graphite.

There is not an equal amount of graphite entering the core as there is boron. The graphite exits towards the lower core, replaced by boron.

 

[Morbius]

There is not an equal amount of graphite entering the core as there is boron. The graphite exits towards the lower core, replaced by boron.

Either way - it's still a monumentally DUMB idea to have graphite followers
on the control rods.

Dr. Gregory Greenman
Physicist

 

[jdsneeder]

NUREG-1250 has detailed description of the Chernobyl design and accident if you can find a copy (didn't see it on their wed site)

When the rods were fully withdrawn, the bottom and top meter of the rod were water and the middle 5m was graphite. So when the rods were inserted, the bottom meter of water was replaced by the graphite as Homer described.