Chernobyl The steps of Chernobyl and effects of radiation

[the_force]

Hi there,

Can anyone answer a few questions I have about chernobyl and related. I am doing some research on something related, and its hard to get good information about this. Here they are.

1) - Can someone explain the steps of the disaster? I mean, let's say is the cooling system failed, what were the physical factors that happened. Did the core heat WAY up? I thought it had something to do with steam bubbles?

2) - This is a question based on the answer to the first question - How is radiation released, what causes the Uranium to release this radiation, and how come it is not released under normal opperation conditions?

3) - Can anyone explain any extraordinary effects this radiation had? Can you explain how this type of radiation effects humans? And how it effects/kills them so fast (They said direct exposure kills under 1 hour! ? )

That would be great if you could answer these. Thank you and take care.

 

[FredGarvin]

If you haven't, take a look a this web site. It has some great info on Chernobyl and really is a great read.

http://www.kiddofspeed.com/chapter1.html

She gives a brief description of the events here:

On the Friday evening of April 25, 1986, the reactor crew at Chernobyl-4, prepared to run a test the next day to see how long the turbines would keep spinning and producing power if the electrical power supply went off line. This was a dangerous test, but it had been done before. As a part of the preparation, they disabled some critical control systems - including the automatic shutdown safety mechanisms.

Shortly after 1:00 AM on April 26, the flow of coolant water dropped and the power began to increase.

At 1:23 AM, the operator moved to shut down the reactor in its low power mode and a domino effect of previous errors caused an sharp power surge, triggering a tremendous steam explosion which blew the 1000 ton cap on the nuclear containment vessel to smithereens.

Some of the 211 control rods melted and then a second explosion, whose cause is still the subject of disagreement among experts, threw out fragments of the burning radioactive fuel core and allowed air to rush in - igniting several tons of graphite insulating blocks.

Once graphite starts to burn, its almost impossible to extinguish. It took 9 days and 5000 tons of sand, boron, dolomite, clay and lead dropped from helicopters to put it out. The radiation was so intense that many of those brave pilots died.

It was this graphite fire that released most of the radiation into the atmosphere and troubling spikes in atmospheric radiation were measured as far away as Sweden - thousands of miles away.

You'll have to get other answers from the nuclear experts around here.

 

[FunkyDwarf]

well the last one is basically doing youre assignment for you but ill give you some pointers

1.) not entirely sure, i used to know but i forgot the details. all i know is it wasnt a nuclear explosion. the pressure built up and the dome imploded as the concrete melted, i think. it then exploded.

2.) radiation in this situation is due to nuclear fission, a term which you can easily look up and get oodles of information. radiation is emitted under normal conditions from uranium as it undergoes radioactive decay, but fission releases far more.

3.) radiation damages humans because the energy particles/waves interact with and damage DNA molecues in a way that causes mutation and/or irrepairable damage

EDIT: damn fred submitted his as i was typing mine :P

 

[Morbius]

Hi there,

Can anyone answer a few questions I have about chernobyl and related. I am doing some research on something related, and its hard to get good information about this. Here they are.

1) - Can someone explain the steps of the disaster? I mean, let's say is the cooling system failed, what were the physical factors that happened. Did the core heat WAY up? I thought it had something to do with steam bubbles?

the_force,

The Chernobyl reactor, the RBMK; is a BAD design. It was a scale-up of a Soviet
nuclear weapons production reactor. The RBMK was dual-use; it produced fuel for
nuclear weapons as well as power.

Even so; the main cause of the Chernobyl accident, as with the Three Mile Island
accident; was STUPID operators! The operators had planned running an experiment
on the Chernobyl reactor [ a poorly planned experiment, at that]. They lowered the
power in preparation for the experiment.

However, the grid load controller in Kiev [ the people that run the electric system ]
called the plant and requested that they remain online at the reduced power because
Kiev needed the electricity. It was 12 hours later before the load controller let the
plant go offline.

When you shutdown or reduce power on a nuclear reactor, there is a temporary
build-up of a neutron poison; Xenon-135. This is called a "Xenon transient" - the
effects of which will disappear in under 24 hours if the reactor is left shutdown.

However, when the load controller released the Chernobyl reactor to go offline - they
were right in the middle of this Xenon transient. The Xenon makes it difficult for the
reactor to operate. But the operators wanted to run the experiment.

So they bypassed all the safety systems! They pulled the control rods out farther
than the safety systems would have allowed them to do otherwise. Because of the
design of the RBMK control rods that have a "non-poison follower"; this is a
particularily DUMB thing to do. It means that if you request an emergency shutdown
or SCRAM of the reactor; the control rods will cause power to INCREASE before
they DECREASE power. [ Such a design is NOT PERMITTED in the USA. ]

The reactor was in a VERY UNSTABLE condition due to the low power and Xenon transient.
Then the operators ran their experiment! KABOOM. They had a fast release of
energy which blew the reactor open. The RBMK is graphite moderated. Most of
the volume of the reactor is graphite - the stuff that's in the "lead" of your #2 pencil.
It's like charcoal, and when exposed to the air at high temperature; the graphite
caught fire and started to burn. It was the heat and convection of the fire that
spread the radioactivity.

The main problem at Chernobyl was that the operators weren't THINKING!
They were so intent about running their experiment, they didn't stop and
think about what was really happening in the reactor. The safety systems
tried to stop them; and they overrode the safety systems because the
safety systems weren't going to let them do their experiment!

2) - This is a question based on the answer to the first question - How is radiation released, what causes the Uranium to release this radiation, and how come it is not released under normal opperation conditions?

Under normal conditions, the radioactive atoms are "locked" in fhe fuel. The
radioactive fission products, the remanants of Uranium atoms that have split can't
move because they are surrounded by Uranium atoms. [ Uranium is hardly radioactive
at all. You can safely hold unirradiated Uranium in the palm of your hand. It is the
remnants of split Uranium atoms that are so radioactive.]

Additionally, the fuel is encased in Zirconium tubes that prevent the escape of the
radioactive atoms. The entire core of Zirconium-encased Uranium is locked in a
sealed reactor vessel.

The whole building around the reactor, called a "containment building" - the big
cylindrical buildings you see at a reactor plant, is also sealed. Courtesy of
Wikipedia; an aerial view of the Braidwood nuclear power plant in Illinois:

http://www.wikimapia.org/#y=41244285&x=-88228626&z=17&l=0&m=a

[Zoom in on the two cylindrical builings in the center of the picture. Those are
the containment buildings for the two reactors at Braidwood. ]

These buildings are shaped / constructed to take great pressure; so they can
"bottle up" any accident. They are the final layer in a multi-layer defense that
protects the public and environment.

3) - Can anyone explain any extraordinary effects this radiation had? Can you explain how this type of radiation effects humans? And how it effects/kills them so fast (They said direct exposure kills under 1 hour! ? )

It depends on how high the radiation dose rate is. However, at very high rates; those
that will kill in under an hour, the radiation affects your nervous system. Your body
is controlled by an "electrical system" called the nervous system. This system
conveys the control signals that regulate the proper operation of your body. With a
high enough radiation field, those signals are disturbed, and your body doesn't
operate properly. Can you imagine how long an airliner would continue to fly if
someone damaged all the electrical and hydraulic systems the pilots use to control
the plane?

Dr. Gregory Greenman
Physicist

 

[Astronuc]

2) - This is a question based on the answer to the first question - How is radiation released, what causes the Uranium to release this radiation, and how come it is not released under normal opperation conditions?

Supplementing Morbius comments -

1) As Morbius indicated, the decay of U releases little radiation. On the other hand, the fission of U creates the radiation in a reactor. The absorption of a neutron (capture) causes U-235 to become an excited U-236, which is unstable and emits a gamma ray or fissions.

The fission process creates two new nuclides (fission products), which are themselves radioactive (hence radionuclides), and releases prompt neutrons (usually 2 or 3). These prompt neutrons are necessary to fission more atoms, but some are absorbed by the structure, which then becomes radioactive. Most fission products decay by beta-emission (and a few by positron emission or electron capture) and gamma-decay. Some fission products release neutrons, and it is these delayed neutrons that allow for the control of the nuclear reaction. The Chernobyl accident was an example of a prompt critical excursion, which happens in fractions of a second and there is no time for humans to respond. As Morbius indicated, the experiment should never have been permitted.

2) In most power reactors, U is in the form of ceramic grade UO₂ which is usually clad in an alloys of Zr. The UO₂ is usually in the form of right circular cylinders or pellets. Most fission products are solid, although some have low melting points or are volatile (e.g. I, Br, Cs), and others are gaseous (Xe, Kr - fission gases).

As long as fission products stay in the fuel, they simply emit the beta and gamma radiation - through the cladding. This is why spent nuclear fuel is stored underwater (which also provides a cooling medium) and after a while the fuel may be stored in canisters of steel or concrete.

Ultimately the fuel may be reprocessed or sent to a repository for burial. If the fuel is reprocessed, the fissile/fertile material can be reused, but the fission products must be calcined into a solid form, which is then encapsulated, and that form is buried in a repository.

In US, most of Europe, and elsewhere, power reactors are contained in a containment structure as Morbius mentioned. This structure is several meters thick - stainless steel lined inside reinforced concrete. It is designed to 'contain' any accident of the reactor and primary cooling system. Chernobyl had no effective containment - it was housed in a conventional metal building structure, which blew apart in explosion.

For thorium - see - http://www.world-nuclear.org/info/inf62.htm

Any fission process whether conventional fission or accelerator driven reactor will produce radioactive fission products - that is inherent in the process - that is where the thermal energy originates.

 

[the_force]

Hey

Wow, thank you all for the VERY fast reply! Also, thanks you Morbius for the detailed reply :)

EDIT: Thank you also Astronuc for the detailed reply :)

I just have 2 more questions, One for my research and one for my own personal interest.

1- (research) - RBMK design - sorry if this is a vauge question - but how does the RBMK design work? How does it get energy form the Uranium?

2 - (Personal Interest) - In the RBMK, or any reactor they have to keep the core cool correct? They use distilled water as a coolent? My question is, if the coolent system for some reason fails, and there is no way to cool the reactor, can you simply turn off the reactor? If not, and the core continues to heat up, what are the possible outcomes of this?

Thank you all again for the great help. Take care.

-Force

 

[Morbius]

In US, most of Europe, and elsewhere, power reactors are contained in a containment structure as Morbius mentioned. This structure is several meters thick - stainless steel lined inside reinforced concrete. It is designed to 'contain' any accident of the reactor and primary cooling system. Chernobyl had no effective containment - it was housed in a conventional metal building structure, which blew apart in explosion.

Argonne National Laboratory used to have a graphic posted on their website which
showed a diagram of the RBMK reactor. The portion of the building above the
reactor floor has WINDOWS at the top! There was absolutely NO pressure
containment capability in the RBMK reactor building.

EDIT: Here's the graphic referred to above, look under the heading of "Infrastructure Development":

http://www.rae.anl.gov/research/ins/

You may need to enlarge the graphic, but look above the red bridge crane, up next to the red truss
at the top of the building; the wall has WINDOWS!

Any fission process whether conventional fission or accelerator driven reactor will produce radioactive fission products - that is inherent in the process - that is where the thermal energy originates.

EXACTLY! How the fission process is driven, whether an accelerator-driven
sub-critical system, or a self-driven critical system is immaterial vis-a-vis the
meltdown question.

The energy to melt the core comes from decay heat, not fission heat; and decay
heat is inherent in either system.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

1- (research) - RBMK design - sorry if this is a vauge question - but how does the RBMK design work? How does it get energy from the Uranium?

Fuel assemblies are loaded into pressure tubes in the reactor. The pressure tubes are arranged through the graphite which provides moderation. This is similar concept to CANDU which uses heavy water for moderation.

The pressure tubes allow water to flow through the assemblies and away from the graphite. The uranium in the fuel is fissioned by neutrons, and each fission releases about 205 MeV of energy of which about 168 MeV are in the form of kinetic energy of the two radionuclides (fission products) formed by the fission of the U (Pu) nucleus. The thermal energy from the fission process is conducted through the fuel to the water, and the water is heated as it passes through the fuel. Heat from the primary system can be sent to a large heat exchanger where it is transferred to more water which is boiled at a lower pressure. The steam is passed to a turbine (which converts thermal energy to mechanical energy) and turbine then turns an electrical generator (convers mechanical to electrical energy).

A reasonable description - http://en.wikipedia.org/wiki/RBMK
RBMK - Реактор Большой Мощности Канальный

http://en.wikipedia.org/wiki/Nuclear_fuel - shows RBMK fuel assembly.

At commissioning of a core, neutron sources (Sb-Te photoneutron source, or Pb-Be source) are necessary to initiate the fission process. The sources also allow the reactor to approach criticality under control. Once sufficient transuranic isotopes accumulate in re-inert fuel, one can do a 'sourceless' startup using the neutrons from spontaneous fissions.

Control rods containing neutron absorber materials are inserted in the core to slow down or shutdown the reactors. The RMBK and VVER-440's use control fuel assemblies, and I concur with Morbius that it is a bad idea.

Control materials are boron compounds (e.g. B₄C), Ag-In-Cd (common in western reactors), Dy-titanate (Russian idea) and Hf. Hf was tried in western reactors, but it absorbed hydrogen from the coolant and the Hf swelled causing the stainless steel (SS304, or SS316) structural material to crack. Cracked control elements is a big NO-NO in the industry.

2 - (Personal Interest) - In the RBMK, or any reactor they have to keep the core cool correct? They use distilled water as a coolent? My question is, if the coolent system for some reason fails, and there is no way to cool the reactor, can you simply turn off the reactor? If not, and the core continues to heat up, what are the possible outcomes of this?

Commercial power reactors used purified, demineralized water for cooling. The water has very low electrical conductivity and typically ppb levels of contaminants - i.e. corrosion products.

If the cooling system fails, the control rods are inserted rapidly into the core to shutdown the system. In water cooled systems, there are safety injection systems attached to the primary cooling system that allow borated water to be injected into the core (part of the Emergency Core Cooling System - ECCS).

If the cooling system fails, the core could heat up - as happened at TMI. If the core heats to a certain point and pressure builds up, then the primary system may fail and the fuel and fission products could escape into the containment building. If there is a power excursion like Chernobyl or SL-1, and explosion may occur with the resulting dispersal of the fuel. Western plants have concrete and steel containment buildings to 'contain' the consequences of reactor/primary system breaches - and also to keep out large objects (generically - missiles) that could harm the reactor system.

 

[the_force]

Hey

Once again, thank you very much for the informative reply - You have answered all my questions :)

I wanted to ask this one last thing:

I have heard (Again, sorry for being vauge) that is the core heats up far past where it should be, and nothing can cool it down, and melts through the reactor, it would hit the Earth and either split the Earth or melt its way through a good portion of the ground. Is that possible?

Take care,
-Adam

 

[Astronuc]

I have heard (Again, sorry for being vauge) that is the core heats up far past where it should be, and nothing can cool it down, and melts through the reactor, it would hit the Earth and either split the Earth or melt its way through a good portion of the ground. Is that possible?

No. The mat of steel and reinforced concrete would contain the core. Part of the core of Chernobyl did melt and flow to lower points in the structure - beneath the core. There it solidified into what has been called the "elephant's foot".

http://www.angelfire.com/extreme4/kiddofspeed/afterword.html

http://en.wikipedia.org/wiki/Image:Pictureofchernobyllavaflow.jpg
http://en.wikipedia.org/wiki/Chernobyl_disaster

http://www.spaceman.ca/gallery/chernobyl - good images
http://www.spaceman.ca/gallery/chernobyl/f421 - lava
http://www.spaceman.ca/gallery/chernobyl/fruin11m - elephant's foot
http://www.spaceman.ca/gallery/chernobyl/sark3b - another view

There is concern that material from a molten core could cause a steam explosion, however the water would likely boil, and the steam boiling on the surface of the molten core would solidify it and reduce the heat transfer rate. If one has seen lava in the ocean, it boils very locally as the lava oozes into the water. In order to have a steam explosion, the would have to be somewhat finely dispersed.

 

[Morbius]

I have heard (Again, sorry for being vauge) that is the core heats up far past where it should be, and nothing can cool it down, and melts through the reactor, it would hit the Earth and either split the Earth or melt its way through a good portion of the ground. Is that possible?

Adam,

One of the key words in your question is "IF".

One can postulate a scenario like you phrase above; however when you do that, you
are totally discounting all the measures taken to prevent the scenario.

As Astronuc explained, there are design features of nuclear power plants designed
to stop the scenario you envision.

One of my Professors tells the story that he gets asked that type of question all the
time; what if the core melts, and the containment fails, and...

He replies "What if two 747 airliners were to collide over Pasedena, and they crashed
into the Rose Bowl stadium, and it happened to be New Years Day while the
Rose Bowl game was being played with tens of thousands of people in attendance,
and the flaming wreckage of the 747s kill all the people in the stadium..."

At which point the person asking the question usually gets upset and says something
like "Don't be ridiculous - that scenario is totally contrived!". The Professor would
then reply, "Not as contrived as the one YOU gave!"

The point being, is that one can dream up strange scenarios - and that's good,
because that tells us what we have to protect against. However, you also have
to be mindful of the the probabilities of that event happening, and the measures
taken to prevent it.

If the probability of the event is so low as to be one-millionth the probability that the
Earth gets clobbered with a big asteroid that wipes out all life on the planet, then you
should spend your time worrying about the asteroid and not the power plant.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

One of the key words in your question is "IF".

One can postulate a scenario like you phrase above; however when you do that, you are totally discounting all the measures taken to prevent the scenario.

One of my Professors tells the story that he gets asked that type of question all the time; what if ...

I once heard a person ask, what if a nuclear plant was hit by a hydrogen bomb or asteroid, to which the lecturer answered - "if someone detontated a hydrogen bomb or an asteroid hit, the last thing I'd worry about is the plant".

As Morbius points out, one can ask "what if . . ." until sheep fly, but if one is asking "what if" about a highly unlikely, improbable or impossible situation, e.g. "what if gravity reversed" or "what if the Earth suddenly stopped spinning?", then we stop dead in our tracks.

Instead we spend our time thinking about what might actually happen and we engineer ways to deal with it and mitigate the consequences. Then there are further studies and experiments to better understand accidents and prevent them or at least mitigate the consequences. That's part of being a good engineer or scientist.

 

[Morbius]

As Morbius points out, one can ask "what if . . ." until sheep fly, but if one is asking "what if" about a highly unlikely, improbable or impossible situation, e.g. "what if gravity reversed" or "what if the Earth suddenly stopped spinning?", then we stop dead in our tracks.

Astronuc,

One of the Bay Area radio stations has a talk show host who answers questions on
science. He is a former Professor at Berkeley and was formerly on staff at the lab
where I work.

When people ask him some of these "what if" questions; especially the ones that
don't really have an answer, his reply is:

"I want you to IF in one hand, and SPIT in the other; and tell me which hand has the most"

Instead we spend our time thinking about what might actually happen and we engineer ways to deal with it and mitigate the consequences. Then there are further studies and experiments to better understand accidents and prevent them or at least mitigate the consequences. That's part of being a good engineer or scientist.

EXACTLY! Being concerned about what might actually happen, and not with
fantasies that are meant to scare people; is what being a good scientist or engineer
is all about.

Dr. Gregory Greenman
Physicist

 

[marcusl]

Morbius and Astronuc, your first two posts here were very informative and interesting. I had followed all the news on Chernobyl as it unfolded in the papers and television, but it's nice to have an accurate post-mortem analysis. I had never heard about Xenon and the power grid. Thanks!

 

[Morbius]

I had never heard about Xenon and the power grid. Thanks!

marcusi,

Here's a rather technical report on Chernobyl from the IAEA:

http://www-pub.iaea.org/MTCD/publications/PDF/Pub913e_web.pdf

There's a good summary of the causes of the accident starting on page 23
as marked in the report.

On page 19 of the report; the issue of the ad hoc modification of the
experimental procedures is addressed:

"When the reactor power could not be restored to the intended level of
700 MW(th), the operating staff did not stop and think, but on the spot
they modified the test conditions to match their view at that moment of
the prevailing conditions."

Addendum:

When explaining the "Xenon transient", I have oft used what I call my
"two bathtub analogy"; two bathtubs, one above the other representing
the levels of I-135 and Xe-135. The two bathtubs obey the same
form of the diffential equations as does the I-135 / Xe-135 balance
equations. I found a paper that also uses a form of this analogy in
some class notes from McMaster University at:

http://www.nuceng.ca/ep6p3/class/Module3D_XenonJun21.pdf

See pages 6/14 and 10/14

Dr. Gregory Greenman
Physicist

 

[the_force]

Hey

Thank you very much the for details and informative replies.

It is human nature for us to think of the worst possible outcome, nevermind if that outcome is possible or not, we as human must worry about something. I unfortunately am in the business of risk and analysis, so this is something I have to deal with everyday. If people take the time to learn something, they might not need to worry as much as they presently do.

Rational minds cannot save us I am afraid :)

The reason people do not worry about something like an asteroid is because we did not make the asteroid, and even though an asteroid could wipe out our plannet, we still worry about a malfunction in a nuclear reactor, and even if measures have been taken to limit certain negative outcomes, it is still something that we control and have made, so by nature, it has flaws.

I find it funny how people think. How many people has Uranium killed in our lifetime? 500k, 1M ? - The general public still fears it, yet smoking kills 5million per year!

-Adam

I once heard a person ask, what if a nuclear plant was hit by a hydrogen bomb or asteroid, to which the lecturer answered - "if someone detontated a hydrogen bomb or an asteroid hit, the last thing I'd worry about is the plant".

As Morbius points out, one can ask "what if . . ." until sheep fly, but if one is asking "what if" about a highly unlikely, improbable or impossible situation, e.g. "what if gravity reversed" or "what if the Earth suddenly stopped spinning?", then we stop dead in our tracks.

Instead we spend our time thinking about what might actually happen and we engineer ways to deal with it and mitigate the consequences. Then there are further studies and experiments to better understand accidents and prevent them or at least mitigate the consequences. That's part of being a good engineer or scientist.

Astronuc,

One of the Bay Area radio stations has a talk show host who answers questions on
science. He is a former Professor at Berkeley and was formerly on staff at the lab
where I work.

When people ask him some of these "what if" questions; especially the ones that
don't really have an answer, his reply is:

"I want you to IF in one hand, and SPIT in the other; and tell me which hand has the most"



EXACTLY! Being concerned about what might actually happen, and not with
fantasies that are meant to scare people; is what being a good scientist or engineer
is all about.

Dr. Gregory Greenman
Physicist

 

[the_force]

Hey

I have another question about radiation, mainly the type that was given off in Chernobyl (Reactor)

some of you gave a good example of what it does by effecting out CNS, so it's like the electrical system of a car shutting down.

Can you give me an example of a healthy person, walking into an area of very high radiation levels, much like the fireman that tried to put out the fire at Chernobyl and what that person would experience? I understood they died within hours, so what would be the first thing that would happen to them?

I am planning on going to Chernobyl (well, to whatever check point I can get to) because it has been a great interest of mine for quite some time.

Thank you all for the great help :)

-Adam

 

[Astronuc]

The effect of radiation depends upon the dosage.

At low levels it would be like getting a sunburn - erythema.

As the dosage increases the damage internally increases, which is essentially radiation poisoning.

At high doses, nerve damage is done and paralysis or death will occur. Before nerve damage, there is an effect like blood poisoning and damage to the alimenary system. Nausea and vomiting would be symptoms.

This a reasonable article.
http://en.wikipedia.org/wiki/Radiation_poisoning

At Chrenobyl, radioactive material was scattered over the immediate area as well as emanating from the core. Since the core was burning, the fission products and fuel were vaporized or aerosolized and the radiaoactive material was then carried up and out. Elements like Cs, Sr and I were carried away on the wind. Cs is chemcially like Na, K, and Sr is like Ca, so they can be taken into the body in place of those elements. I of course is absorbed by the thyroid gland and too much radiation will damage or destroy the thyroid, which produces hormones that provide important regulatory function in the body. That is why radiation protection is crucial.

 

[Morbius]

The reason people do not worry about something like an asteroid is because we did not make the asteroid, and even though an asteroid could wipe out our plannet, we still worry about a malfunction in a nuclear reactor, and even if measures have been taken to limit certain negative outcomes, it is still something that we control and have made, so by nature, it has flaws.

Adam,

In the case of nuclear power, I think it's more than just because it is
man-made.

First, when the power of nuclear energy is deliberately made into a
destructive force; it is by far more destructive than chemical based
explosives. This is how the world was introduced to nuclear energy;
the use of the A-bombs ending World War II.

Secondly, nuclear power is a victim of its own record of safety. Airplanes
are also man-made, and every few years, an airliner crashes and kill a few
hundred people. People accept that risk.

Nuclear power has fewer accidents; only 1 major commercial power plant
accident in the USA; which didn't harm the public. In the absence of
the familiarity of airliner crashes; the imagination of the public took over;
especially when stoked by anti-nuclear activists that had no scrupples
in presenting a truthful view. Scare stories about "China Syndromes"
ran rampant.

Third, the effects of radiation are not directly perceivable by our senses.
Hence, that "unknown" factor which causes one's imagination to go wild.
Nuclear danger could "get you" and you wouldn't know it until it was too
late. That's the "boogeyman" that was stoked by the activists.

Hence, an industry which is actually the safest, has a reputation for
being the most risky.

Dr. Gregory Greenman
Physicist

 

[the_force]

Adam,

In the case of nuclear power, I think it's more than just because it is
man-made.

First, when the power of nuclear energy is deliberately made into a
destructive force; it is by far more destructive than chemical based
explosives. This is how the world was introduced to nuclear energy;
the use of the A-bombs ending World War II.

Secondly, nuclear power is a victim of its own record of safety. Airplanes
are also man-made, and every few years, an airliner crashes and kill a few
hundred people. People accept that risk.

Nuclear power has fewer accidents; only 1 major commercial power plant
accident in the USA; which didn't harm the public. In the absence of
the familiarity of airliner crashes; the imagination of the public took over;
especially when stoked by anti-nuclear activists that had no scrupples
in presenting a truthful view. Scare stories about "China Syndromes"
ran rampant.

Third, the effects of radiation are not directly perceivable by our senses.
Hence, that "unknown" factor which causes one's imagination to go wild.
Nuclear danger could "get you" and you wouldn't know it until it was too
late. That's the "boogeyman" that was stoked by the activists.

Hence, an industry which is actually the safest, has a reputation for
being the most risky.

Dr. Gregory Greenman
Physicist

I agree with you 100%

Do you think that the world would be a different place if Nuclear energy was not introduced in the form of a bomb?

 

[russ_watters]

Secondly, nuclear power is a victim of its own record of safety. Airplanes
are also man-made, and every few years, an airliner crashes and kill a few
hundred people. People accept that risk.

Nuclear power has fewer accidents; only 1 major commercial power plant
accident in the USA; which didn't harm the public. In the absence of
the familiarity of airliner crashes; the imagination of the public took over;
especially when stoked by anti-nuclear activists that had no scrupples
in presenting a truthful view. Scare stories about "China Syndromes"
ran rampant.

Interesting theory and largely true, but there is a difference that makes the anti-nuclear fear more understandable (even if it is equally wrong): Astronuc's 747s over the rose bowl (and 911) aside, the worst that can happen in a plane crash is you kill a few hundred people. If Chernobyl had been Limerick (I live in the adjacent town), Philadelphia might be uninhabitable today. And one or two TMI type accidents a decade won't de-senstize the population into accepting that Chernobyl can't happen here. You almost have to be an engineer to understand just how spectacularly bad the Chernobyl engineering and operation had to be to make that accident happen - and why as spectacularly bad as the operation was at TMI, it couldn't have turned out much worse than it did.

The best we can hope for is that people accept the risk - or accept the word of scientists and engineers that the risk is low. People are still afraid of flying, but they still do it because they are somehow able to put a little trust into the engineers who figured out how to make hundred-thousand pound hunks of metal fly. Yes, that is largely because people see that big planes only fall out of the sky about once a year, but it is still a leap of faith for some people: That never stopped an aunt and uncle of mine from driving to the airport together and then taking separate planes to their destination to mitigate the risk of their kids growing up orphans.

 

[selfAdjoint]

Do you think that the world would be a different place if Nuclear energy was not introduced in the form of a bomb?

We have to make a lot of assumptions for that. Starting the split from, say 1918, we have to assume that Wilson didn't have a stroke and was able to "persuade" France not to impose a severe punitive peace on Germany, so that the Weimar Republic didn't have the unsolvable public debt problem and was able to survive the challenge from the right wing radicals like the Nazis. (Assassinating Hitler wouldn't help; he wasn't the only leader and what eventually became the Nazis wasn't the only organization looking to subvert and destroy the republic).

So assuming there was no flight of physicists to the US, and the big players stayed in Germany and invented peaceful nuclear power, which is entirely believable under those priors, we would be in a world where nuclear power had no nasty implications.

The problem of the Soviets I have just ignored. If they were not attacked, if there was no "Great Patriotic War" then their development would be incalculably different than in our world, but it's reasonable to believe that they wouldn't go on any Marxist crusade and would confine themselves to their own borders. Somebody down the line is going to see and develop nuclear weapons, but who it would be is again incalculable as is the date of it. It is reasonable toassume, though, that it would happen after there was a solid nuclear power industry in place. Paging Harry Turtledove.

 

[Astronuc]

I imagine that during the 1950s through 1970s, nuclear was associated with nuclear weapons and nuclear attack, and many people had seen images of nuclear bombs devastating large areas. Civil defense drills were part of the educational process into the late 1960s or early 70s.

Then in 1979, the TMI accident shocked the nation and then later in 1986 the Chernobyl disaster.

As a result of the TMI accident, greater scrutiny was given to the design and construction of nuclear power plants, and many were given upgrades for safety reasons. Accident analyses became more sophisticated. And very importantly, training of personnel became much more detailed. TMI-2 has only operated for about 62 effective full power days, i.e. they were early into the first cycle, so the operators did not have vast experience, although they probably had experience with normal operation from the other unit. There were several performance problems involved, and nobody really understood the details of what was really happening during the event.

Here is the wikipedia article - http://en.wikipedia.org/wiki/Three_Mile_Island - but it does contain some errors/inaccuracies. However, the main points are correct -

The operators did not initially recognize the accident as a Loss of Coolant Accident (LOCA) since they had only ambiguous reactor water level indication and failed to properly interpret other indications of a LOCA.

Meanwhile, another problem appeared elsewhere in the plant with the emergency feedwater system, the main feedwater system's backup. Three emergency feedwater pumps started automatically following the loss of the main feed pumps, but two valves on the emergency feedwater lines were shut, preventing the feedwater from reaching the steam generators. The emergency feedwater system had been tested 42 hours prior to the accident. As part of the test, these valves were closed but should then have been reopened at the end of the test. But on this occasion it appeared that through either an administrative or human error, the valves were not reopened. . . . .

 

[Morbius]

Interesting theory and largely true, but there is a difference that makes the anti-nuclear fear more understandable (even if it is equally wrong): Astronuc's 747s over the rose bowl

russ,

The 747 / Rose Bowl scenario is mine.

(and 911) aside, the worst that can happen in a plane crash is you kill a few hundred people. If Chernobyl had been Limerick (I live in the adjacent town), Philadelphia might be uninhabitable today.

Even then; Kiev is less than 80 miles from Chernobyl; and it's not
uninhabitable. Philadelphia is more than 100 miles from Limerick.

Additionally, Limerick isn't an RBMK. What happened at Chernobyl
can't happen in a USA-type LWR with containment.

And one or two TMI type accidents a decade won't de-senstize the population into accepting that Chernobyl can't happen here.

Here's an analysis by a psychiatrist:

http://www.pbs.org/wgbh/pages/frontline/shows/reaction/interviews/dupont.html

You almost have to be an engineer to understand just how spectacularly bad the Chernobyl engineering and operation had to be to make that accident happen - and why as spectacularly bad as the operation was at TMI, it couldn't have turned out much worse than it did.

In the USA, there has been a loss of trust of scientists and engineers, and
technology in general. So often we hear of the "study du jour" of what
will cause cancer, or harm us in some way; cancer from powerlines, or
brain tumors from cell phones...and the public asks why did scientists
and engineers inflict this on us.

The French trust and are proud of their scientists and engineers. Also
from Frontline:

http://www.pbs.org/wgbh/pages/frontline/shows/reaction/readings/french.html

The best we can hope for is that people accept the risk - or accept the word of scientists and engineers that the risk is low.

Unfortunately, scientists and engineers are perceived to have a vested
interest in the technology. Activists aren't seen as having an interest;
so their views are better accepted.

Trust won't work; education is the key. People have to know WHY
nuclear power is safe, and not go on trust.

That's one of the VERY POSITIVE aspects of this Forum; people can
learn for themselves. For example, another thread served to dispel the
notion held by a poster that modern critical nuclear reactors would
"Fail Unsafe".

People are still afraid of flying, but they still do it because they are somehow able to put a little trust into the engineers who figured out how to make hundred-thousand pound hunks of metal fly. Yes, that is largely because people see that big planes only fall out of the sky about once a year, but it is still a leap of faith for some people: That never stopped an aunt and uncle of mine from driving to the airport together and then taking separate planes to their destination to mitigate the risk of their kids growing up orphans.

Additionally, the alternatives to air travel; trains, buses and cars are
more time consuming. So the traveling public doesn't have a quick
alternative to air travel.

There are other alternatives to nuclear power that deliver the same
electricity at the wall plug. The differences, like increase CO2 pollution
from the alternatives, are not directly perceived.

Dr. Gregory Greenman
Physicist

 

[Morbius]

TMI-2 has only operated for about 62 effective full power days, i.e. they were early into the first cycle, so the operators did not have vast experience, although they probably had experience with normal operation from the other unit. There were several performance problems involved, and nobody really understood the details of what was really happening during the event.

Astronuc,

Late in 1979, while I was still a graduate student at MIT; we had
Professor Kemeny, who headed the TMI investigation; give us a seminar
on the accident and the investigation.

Professor Kemeny said he toured the TMI-2 control room and talked with
the operators. He then asked for them to get a "steam table" - a book
that details the Equation of State for water. It took the operators a
little more than a half-an-hour to scare up a "steam table".

Kemeny said the operators were not thinking about the Equation of State
of water in their pressurized system. He said that would be obvious if
we had read the chronology.

I knew exactly what he meant. I remember reading the Boston Globe at
my desk the morning after the accident. The chronology stated that the
operators had "stabilized" the reactor at a certain pressure and a certain
temperature.

I wondered how far away the reactor coolant had come to boiling. So I
reached up onto the filing cabinet next to my desk to get my copy of
Keenan and Keyes "Steam Tables"; and looked up the pressure and
temperature conditions given in the newspaper on the water phase
diagram. Those conditions were ON the saturation line!

Stabalize?! Hell - they were BOILING; which you don't want to do in a
PWR!

That's the BIG problem that Kemeny told us about. When the pressure
and temperature of the reactor coolant shown by the instruments stopped
changing; the operators thought they had stabilized the reactor and the
problem was essentially solved - at least it wouldn't get worse.

In point of fact, the worse was happening; the coolant was boiling away,
uncovering the core, leading to a meltdown; and the operators were
totally clueless!

It would be like the pilots of an airliner "trimming out" the plane after a
bit of turbulence, but trimming the plane into a gentle dive, and thinking
that they didn't need to do anything further - not noticing the plane was
in a dive on the artificial horizon, or noticing the altitude dropping until
they hit the ground. In aviation circles, that's known as CFT - Contolled
Flight into Terrain - the pilots flew the plane into the ground.

THAT'S essentially what happened at Three Mile Island.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

Morbius,

There were so many things that went wrong at TMI-2. Someone told me that the instrumentation for temperature measurement went off scale becuase the temperatures were outside of the design basis. Someone put a voltmeter on the wires and determined that the temperature in the cores well over several 100 K beyond to top of the scale - IIRC much greater than 600°C or 800°C - and they didn't believe it at first (or they didn't want to believe it). These are temperatures at which Zircaloys are annealed (recrystallized) or softened during fabrication, and in steam, Zircaloy 4 starts oxidizing (corroding) rapidly - particularly at the temperatures in TMI-2. That was when the fuel disintegrated forming a pile of rubble in the bottom of the core. In fact, the core barrel had disintegrated, and some of the fuel/debris had collected against the pressure vessel, and the PV has started to corrode rapidly.

Also, keep in mind that the reactor was in its first cycle, so the exposure of the fuel was relatively low. It could have been a lot worse if the exposure of the fuel was where it is now in many plants.

IEEE did a really good writeup on the TMI accidents sometime in the late 1980's or just after Chernobyl.

Professor Kemeny said he toured the TMI-2 control room and talked with the operators. He then asked for them to get a "steam table" - a book that details the Equation of State for water. It took the operators a little more than a half-an-hour to scare up a "steam table".

This was one of main reasons utilities were forced to have Shift Technical Advisors (STAs) on staff to support the reactor operators.

 

[the_force]

Hey

Trust won't work; education is the key. People have to know WHY
nuclear power is safe, and not go on trust.

I agree with this statement! I blame this partly on the media, only explaning the worst of something, and not educating the general public.

Take a Dirty bomb for instance. You ask any person on the street, and because of the media and movies they think a "dirty" bomb is a nuclear bomb without the mass destruction. From what I understand a dirty bomb just creates psychological harm through ignorance and mass panic.

However, if the general public is educated by the media on the dirty bomb, I guess they can't make anymore movies on it so I guess that's why they still say a dirty bomb could kill half of New York

 

[Morbius]

Morbius,

There were so many things that went wrong at TMI-2. Someone told me that the instrumentation for temperature measurement went off scale becuase the temperatures were outside of the design basis.

Astronuc,

UNTRUE! Coolant temperatures in the early phase of the accident were
actually LOWER than nominal because the reactor was at lower pressure
due to the operation of the pressure relief valve.

Someone put a voltmeter on the wires and determined that the temperature in the cores well over several 100 K beyond to top of the scale - IIRC much greater than 600°C or 800°C - and they didn't believe it at first (or they didn't want to believe it). These are temperatures at which Zircaloys are annealed (recrystallized) or softened during fabrication, and in steam, Zircaloy 4 starts oxidizing (corroding) rapidly - particularly at the temperatures in TMI-2. That was when the fuel disintegrated forming a pile of rubble in the bottom of the core. In fact, the core barrel had disintegrated, and some of the fuel/debris had collected against the pressure vessel, and the PV has started to corrode rapidly.

Yes - these temperatures and conditions occurred AFTER the coolant
had BOILED AWAY!

As Professor Kemeny stated in his seminar; the core NEVER would have
gotten into the state you describe above if the operators had just
realized the coolant was BOILING!

If the operators had consulted their steam tables, and realized the coolant
was boiling away, and turned the emergency core cooling system back on
[they had turned it off] ALL of those other problems would have been avoided.

The main fault was with the operators in the early phase of the accident.
Things did go down hill from there.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

Dirty bombs could be harmful because the objective is to disperse radioactive material over as wide an area as possible. It would certainly disrupt thousands of lives and a local economy around the area affected by the radioactive material.

Any explosion in a populated area is disruptive. A dirty bomb may or may not be similarly disruptive, although part of the disruption is 'psychological', and hence it is a weapon of 'terror', more so than a conventional explosive.

 

[Astronuc]

Astronuc,

UNTRUE! Coolant temperatures in the early phase of the accident were
actually LOWER than nominal because the reactor was at lower pressure
due to the operation of the pressure relief valve.

Yes - these temperatures and conditions occurred AFTER the coolant
had BOILED AWAY!

As Professor Kemeny stated in his seminar; the core NEVER would have
gotten into the state you describe above if the operators had just
realized the coolant was BOILING!

Dr. Gregory Greenman
Physicist

I was reflecting on the later phase of the accident after much of the coolant had boiled away. True, they didn't realize the coolant was boiling.

The accident also highlighted problems with the OTSGs, which are unique to B&W plants. The steam at the top of the hot leg precluded natural convection in the primary loops.

 

[Morbius]

IEEE did a really good writeup on the TMI accidents sometime in the late 1980's or just after Chernobyl.

Astronuc,

I seem to remember that the IEEE article was pretty FLAWED in its account.

I'll have to look it up again to see what was amiss.

The Kemeny report was the best, most authoritative report.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

Just found a site where one can download the Kemeny and Rogovin reports.

http://www.threemileisland.org/resource/index.php?aid=00027

Also a good resource at the Smithsonian

Three Mile Island: The Inside Story
http://americanhistory.si.edu/tmi/tmi12.htm

 

[Morbius]

Dirty bombs could be harmful because the objective is to disperse radioactive material over as wide an area as possible. It would certainly disrupt thousands of lives and a local economy around the area affected by the radioactive material.

Any explosion in a populated area is disruptive. A dirty bomb may or may not be similarly disruptive, although part of the disruption is 'psychological', and hence it is a weapon of 'terror', more so than a conventional explosive.

Astronuc,

Some studies on RDDs or "Dirty Bombs":

From LLNL:

http://www.llnl.gov/csts/publications/sutcliffe/

From MIT's "Technology Review":

http://www.technologyreview.com/read_article.aspx?id=13651&ch=energy
http://muller.lbl.gov/TRessays/29-Dirty_Bombs.htm

Dr. Gregory Greenman
Physicist

 

[Astronuc]

For such weapons, the psychological impact can be greater than the limited harm they are likely to cause.

I don’t mean to suggest that radioactive materials are harmless. Indeed, consider the story of scavengers in Goiania, Brazil, who found and dismantled an abandoned radiotherapy machine in 1987. The machine contained 1,400 curies of cesium-137. (A curie is the radioactivity of one gram of radium.) Two men, one woman, and one child died from acute radiation poisoning; 250 additional people were contaminated. Several of the 41 houses evacuated could not be cleaned adequately and were demolished.

from Muller's page cited by Morbius. I was thinking of exactly this incident.

 

[Morbius]

Just found a site where one can download the Kemeny and Rogovin reports.

http://www.threemileisland.org/resource/index.php?aid=00027

Astronuc,

Thank you.

As the Kemeny report states at the bottom of page 8; the accident could
have been terminated at any time in the first 100 minutes if the operators
had closed the block valve which backs up the stuck relief valve.

The irreversible road to a meltdown was initiated at 100 minutes when the
operators stopped the main coolant pumps because they were vibrating.

The pumps were vibrating because they were pumping not water but a
mix of water and steam. If the operators had known that the coolant
was boiling; they would have known that the pumps were vibrating due
to pumping a 2-phase steam/water mix. The vibrating pumps were an
additional indication of boiling; but the operators didn't pick up on it.

As I recall, that was another of Kemeny's points in the seminar; the
operators concerned themselves with a host of individual problems; they
didn't take an overall "system view" of what was going on. To them it
was a series of small problems; they missed the big problem, the core
was BOILING!

On Vol I, page 35, the Kemeny report states that the operators did not receive
training in "Recognition of saturation [i.e. boiling] conditions in the reactor".

The paragraph beginning at bottom of Vol III, page 5 summarizes the problem
nicely. That echoes Kemeny's statements in the seminar; the operators didn't
have a good understanding of the physics and engineering of the machine they
were operating. They could follow the book, follow the procedures that they
were taught; but if the problem wasn't in the book; they were lost.

When they shutdown the main coolant pumps; they set the reactor on
an irreversible course to destruction.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

A reasonable description and image of PWR NPP.
http://americanhistory.si.edu/tmi/02-10.htm

Discussion of fuel assembly (reasonably accurate)
http://americanhistory.si.edu/tmi/02-08.htm

Schematic of reactor and core
http://americanhistory.si.edu/tmi/02-07.htm

 

[Astronuc]

As the Kemeny report states at the bottom of page 8; the accident could
have been terminated at any time in the first 100 minutes if the operators
had closed the block valve which backs up the stuck relief valve.

The irreversible road to a meltdown was initiated at 100 minutes when the
operators stopped the main coolant pumps because they were vibrating.

The pumps were vibrating because they were pumping not water but a
mix of water and steam. If the operators had known that the coolant
was boiling; they would have known that the pumps were vibrating due
to pumping a 2-phase steam/water mix. The vibrating pumps were an
additional indication of boiling; but the operators didn't pick up on it.

As I recall, that was another of Kemeny's points in the seminar; the
operators concerned themselves with a host of individual problems; they
didn't take an overall "system view" of what was going on. To them it
was a series of small problems; they missed the big problem, the core
was BOILING!

When they shutdown the main coolant pumps; they set the reactor on
an irreversible course to destruction.

Hence the rigorous training, particularly with advanced simulators that the operators can experience real emergency scenarios without putting a real reactor/plant at risk. The simulators, like aircraft simulators, replicate the real physics of the plant.

 

[Morbius]

Hence the rigorous training, particularly with advanced simulators that the operators can experience real emergency scenarios without putting a real reactor/plant at risk. The simulators, like aircraft simulators, replicate the real physics of the plant.

Astronuc,

See Vol III, page 5. The simulator at Babcock and Wilcox couldn't simulate
a TMI-type accident. It couldn't simulate conditions in which the coolant
had voiding [steam] outside of the pressurizer.

The operator training was one of the things that the Kemeny study focused
on; and they concluded it was whoefully inadequate. They stated the
training in the simulator, "...lacked depth", and was limited to only the
immediate actions following rather simple failures.

The operators didn't have a good understanding of the basics.

They were just taught "If 'W' happens, do 'X', and if 'Y' happens, do 'Z'"

There was no "understanding" of the reactor plant. Therefore, if they
hadn't seen the situation before in their training; they were ill-equipped
to figure out what was happening. Vol III, pages 5-7 are damning of the
training program.

Their training also focussed more on how to optimize a properly operating
plant; as opposed to recognizing and dealing with an accident.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

See Vol III, page 5. The simulator at Babcock and Wilcox couldn't simulate
a TMI-type accident. It couldn't simulate conditions in which the coolant
had voiding [steam] outside of the pressurizer.

The operator training was one of the things that the Kemeny study focused
on; and they concluded it was whoefully inadequate. They stated the
training in the simulator, "...lacked depth", and was limited to only the
immediate actions following rather simple failures.

Looking further down page 5, the folks at Davis Besse had experienced a similar event on Sept 24, 1977. The people at B&W knew that, but the information had not been conveyed to the other operators. There is not excuse for this. An advisory should have been transmitted to other operators within 30 days or less!

Although things are better these days, I still encounter some of this today in my work.

The simulators these days are a lot better than they were prior to 1980, and the training is vastly superior. But things still happen that shouldn't.

 

[Morbius]

Looking further down page 5, the folks at Davis Besse had experienced a similar event on Sept 24, 1977. The people at B&W knew that, but the information had not been conveyed to the other operators. There is not excuse for this. An advisory should have been transmitted to other operators within 30 days or less!

Astronuc,

Yes - there was NO EXCUSE for B&W not to highlight the experience of
the Davis-Besse incident. They had about a year and a half!

Around the time of the Kemeny seminar at MIT, we also had a seminar
by the then President of either the American Nuclear Society or the
Atomic Industrial Forum.

Managers at electric utilities hadn't learned the lessons a child learns
when they adopt a pet; with the pleasures of owning a pet also comes
responsibility for the proper care and feeding of the pet.

Utility executives only saw the $$$ advantages in owning a nuclear
power plant. The didn't concern themselves with its proper "care and
feeding".

According to the seminar; first you have to get their attention: "An
accident at your nuclear power plant can BANKRUPT your company".

"Now that we have your attention; it doesn't have to happen; we can
help you".

Nuclear power plants are NOT toys!

Dr. Gregory Greenman
Physicist

 

[Morbius]

from Muller's page cited by Morbius. I was thinking of exactly this incident.

Astronuc,

As I recall, this incident, or a similar occurence in Mexico; was discovered
because a truck set off the radiation detector alarms as it was leaving
Los Alamos.

The truck had contained everyday products that had been manufactured
with reclaimed metals, which included radioactive metals from a disassembled
radiotherapy machine.

Dr. Gregory Greenman
Physicist

 

[Astronuc]

If one visists the NRC website, the vast majority of reportable incidents have to do with misused, missing or misplaced radioactive sources.

Once in a while, something notable from a nuclear power plant is reported. The people at NPPs take their work very seriously. I know because I work with these folks.

 

[Morbius]

If one visists the NRC website, the vast majority of reportable incidents have to do with misused, missing or misplaced radioactive sources.

Astronuc,

Yes - the vast majority of the incidents have to do with old medical
devices. Nuclear power plants are much more highly controlled and
regulated.

Dr. Gregory Greenman
Physicist

 

[Homer Simpson]

The operators didn't have a good understanding of the basics.
They were just taught "If 'W' happens, do 'X', and if 'Y' happens, do 'Z'"
There was no "understanding" of the reactor plant. Therefore, if they
hadn't seen the situation before in their training; they were ill-equipped
to figure out what was happening. Vol III, pages 5-7 are damning of the
training program.
Their training also focussed more on how to optimize a properly operating
plant; as opposed to recognizing and dealing with an accident.

If the operators had consulted their steam tables, and realized the coolant
was boiling away, and turned the emergency core cooling system back on
[they had turned it off] ALL of those other problems would have been avoided.

As the Kemeny report states at the bottom of page 8; the accident could
have been terminated at any time in the first 100 minutes if the operators
had closed the block valve which backs up the stuck relief valve.

Ed Frederick was one of the reactor control room ops involved with TMI incident, and has a presentation about the issues. According to the presentation, the ops were actually heavily trained on system design and interaction information under the belief that if something went wrong, the operators would be able to improvise a solution. There procedures were all based on identifing the failure, not symptoms. The operators at TMI were forced to make a bunch of 'knowledge based' decisions, as opposed to procedure based, and so had a high likelyhood of error. This is what happened when they saw high pressurizer level, they assumed there was plenty of water in the core and shut down the emergency pumps. It was the coolant voiding that caused the high level, but they made a mental error under stress. The procedures were written for a large LOCA which would have much different

also from the presentation:
There were several engineering problems with TMI as well. Firstly was the indication for the pressurizer PV, which indicated closed in the control room. This close indication light was only indication of the demand signal, not a limit switch actual postion. This obviously is a set-up. Also inadequate temperature instrumentation (not ranged for boiling conditions), lack of backup boiler feedwater flow indication, bad alarm system which blazed in 800 non prioritized alarms in the first 14 minutes of the event printed to a printer which did 6 lines per minute. It must have been really hectic, clearly one can see that an operator might not have the oportunity to dust off the old steam tables unless they were in the procedures. (now sub-cooling margin is easily displayed)

Tons of industry changes (design, instrumentation, training, procedures, culture) came about due to the problems recognized at TMI. While its true that TMI had such serious results due to operator action, it was the underlying industry and safety culture problems and deficiancies to cause it that just had not surfaced yet at the time, not a couple individuals.

 

[Morbius]

Tons of industry changes (design, instrumentation, training, procedures, culture) came about due to the problems recognized at TMI. While its true that TMI had such serious results due to operator action, it was the underlying industry and safety culture problems and deficiancies to cause it that just had not surfaced yet at the time, not a couple individuals.

Homer,

When I was in graduate school at MIT, we had a seminar by Prof. Kemeny
who headed up the investigation.

As I recall, Kemeny stated this was first and foremost a failure of INDIVIDUALS
and not the system. There was certainly room for improvement in the
system, and those changes were made.

However, one of the operator's main concerns is whether there is ample
cooling water covering the core. If one has a pressurized system, where
the pressure is varying, as in the TMI core; I don't see how ANYONE could
have failed to consider how far away from the saturation line one was.

When I read the account in the paper the day after, and it said the reactor
was stabilized at a certain temperature and pressure - that's the first thing
I though of - how far away from the saturation line. It turns out, those
conditions were ON the saturation line. They didn't stabilize the reactor;
it was BOILING! [Prof. Kemeny noted this also in his seminar.]

Prof. Kemeny pointed this out as an egregious FAILURE by the operators.
Additionally, the core damage was initiated by the operators turning off the
coolant pumps because they were vibrating.

Prof. Kemeny pointed out that the operators took actions before they
understood the situation, and without considering the consequences of
those actions. The operators were like automatons - they just reacted -
they didn't "THINK"!

You are incorrect that the temperature was out of range. The reactor was
at LOWER pressure than the nominal pressure of the reactor due to the
failure of the PORV to close. Because of the lower pressure, the coolant
temperature was LOWER than nominal, and the instrumentation can certainly
read nominal temperatures in a PWR. Even though the coolant was boiling,
it boiled at temeratures LOWER than nominal PWR temps due to the lower
pressure. Additionally, the printer is a logging device, NOT to be used to
ascertain current conditions.

The take-away message from Kemeny was that these were operators that
didn't THINK.

Dr. Gregory Greenman
Physicist

 

[massspectromete]

The cause of the accidnt

Hi there,

Can anyone answer a few questions I have about chernobyl and related. I am doing some research on something related, and its hard to get good information about this. Here they are.

1) - Can someone explain the steps of the disaster? I mean, let's say is the cooling system failed, what were the physical factors that happened. Did the core heat WAY up? I thought it had something to do with steam bubbles?

2) - This is a question based on the answer to the first question - How is radiation released, what causes the Uranium to release this radiation, and how come it is not released under normal opperation conditions?

3) - Can anyone explain any extraordinary effects this radiation had? Can you explain how this type of radiation effects humans? And how it effects/kills them so fast (They said direct exposure kills under 1 hour! ? )

That would be great if you could answer these. Thank you and take care.

The causes of the accedint concern on the personal error category of the
operator in the control room in which that error is:
Experimental test by lower ans shutdown the reactor(onsite) and depend on
the inertia of the generator to contintue operation the reactor until the
off site source of the electricity will work--so he shutdown but the inertia not help----
one important reason for release the radiation is the error in the defence in
depth methadology (safety analysis) the defect in the barries requied to
protect the station against any release.

 

[curie]

A comment on NPP operators (which may or may not be considered OT, & rambling) : such operators do take their work seriously & are very competent etc etc but they cannot be expected to perform at a high level all the time. They can have as much training & assessment as deemed by the regulators/whoever, but that does not guarantee they will take the correct action at all times and plant is designed to take into account that as far as possible. It is very easy in hindsight to see what could have been done. The wording in the previous posts saying the operators did not think or were stupid comes across as very harsh & implying they were actually incompetent. It is indeed true that at certain times their actions were the cause of or contributed to accidents, but I don't think this warrants calling them generally unthinking or labelled as stupid. They were acting in unplanned (leading into extreme) conditions & no matter how much training one has in so-called "dynamic risk assessment",emergency response, whatever the latest fad is, etc, under those conditions nothing can be guaranteed, including even the operators' own recognition that nothing is guaranteed. Now if "operator" is meant in the sense of plant operator as a whole, the organisation, then that is different, and it is clear that the set up in the FSU at the time of Chernobyl was ludicrous, even given the contemporary ideas of safety.

I have visited Chernobyl and found that the remediation of the affected Unit is progressing barely satisfactorily, but only due to Western input. Anything that does not have Western input is frankly a mess (by Western standards though!). It was very clear that the psychological affect was/is far more damaging and far-reaching. The Chernobyl museum in Kiev is a masterpiece of propoganda. Don't expect many facts if you visit.

 

[Homer Simpson]

Curie: Well said. Operating a NPP is very different from engineering one. When it hits the fan, you can't sit back with a team and engineer the perfect response. That is why it is the organizations responsibility to have perfect procedures and practices to follow in the event of an incident. All these events are drilled into the operator these days, and regularly tested in the simulators.

Every time a transient occurs at a plant now, a transient review team will gather for weeks with fine tooth comb and critique every action the operator took. This leads to OPEX and betters the industry as a whole. In most cases what appeared to be an excellent operator response to a transient will be picked to pieces by the review team and as crap rolls down hill, it always lands right in the operators lap.

Certainly operators do make mistakes, it will happen. However the large picture processes and event training now in place, sparked by past events, ensure that these types of events do not occur. There are procedural paths in place that ensure things like shutting down core cooling pumps (TMI) or interfering with shutdown systems (chern) don't happen. Critical decisions are based on Safety, ALWAYS.

 

[Paulanddiw]

Homer Simpson Movie

I was wondering if you got a cameo in the movie.

 

[Morbius]

Curie: Well said. Operating a NPP is very different from engineering one. When it hits the fan, you can't sit back with a team and engineer the perfect response. That is why it is the organizations responsibility to have perfect procedures and practices to follow in the event of an incident. All these events are drilled into the operator these days, and regularly tested in the simulators.

Homer Simpson,

Yes - but one of the problems with Chernobyl is that the operators were improvising
because they didn't have procedures.

The operators reduced power in the Chernobyl reactor prior to conducting an experiment
as to how much energy they could extract to run cooling pumps in an emergency.

However, the load controller in Kiev called and asked them to remain online a few hours
more because they needed the output from the plant. So Chernobyl stayed on line
about 12 hours more at reduced power.

However, they had been at a higher power, and had equilibrium Iodine-135 levels
corresponding to the higher power. Because they were at lower power than what
the Iodine-135 level was in equilibrium with; the reactor underwent a Xenon transient.

The Iodine-135 decays to Xenon-135; and the reactor power was too low for the
burnup of Xe-135 to match the production due to Iodine-135 decay. So Xe-135
built up in the reactor; just as it does after a shutdown.

After 12 hours at reduced power, the load controller released the plant to go offline.
That's when the operators started their previously planned experiment. However,
they were right in the middle of the reactor's Xenon transient. The core was heavily
Xenon-poisoned and the operators were having trouble maintaining criticality.

That's why the operators did all sorts of things they should not have; like withdrawing
control rods more than what is normally allowed. They were trying to do their experiment
with the reactor in condition that had not been anticipated - namely heavily Xenon
poisoned.

The smart thing for the operators to have done was to realize that they were in abnormal
conditions that had not been anticipated when the experiment was planned. They should
have just shutdown the reactor and saved the experiment for another day. Unfortunately,
they ventured into unknown territory - and the result is history.

Dr. Gregory Greenman
Physicist