# Chernobyl The steps of Chernobyl and effects of radiation

#### Astronuc

Staff Emeritus
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

Dearly Missed
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

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

Last edited:

#### Astronuc

Staff Emeritus
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', moreso than a conventional explosive.

#### Astronuc

Staff Emeritus
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

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

Dearly Missed
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

#### Morbius

Dearly Missed
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', moreso than a conventional explosive.
Astronuc,

Some studies on RDDs or "Dirty Bombs":

From LLNL:

http://www.llnl.gov/csts/publications/sutcliffe/ [Broken]

From MIT's "Technology Review":

http://muller.lbl.gov/TRessays/29-Dirty_Bombs.htm

Dr. Gregory Greenman
Physicist

Last edited by a moderator:

#### Astronuc

Staff Emeritus
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

Dearly Missed
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

Last edited:

#### Astronuc

Staff Emeritus
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

Dearly Missed
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

Last edited:

#### Astronuc

Staff Emeritus
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

Dearly Missed
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

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

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

Nuclear power plants are NOT toys!!

Dr. Gregory Greenman
Physicist

#### Morbius

Dearly Missed
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.

with reclaimed metals, which included radioactive metals from a disassembled

Dr. Gregory Greenman
Physicist

#### Astronuc

Staff Emeritus
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

Dearly Missed
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.

Last edited:

#### Morbius

Dearly Missed
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

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

Last edited:

#### 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, lets 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 catagory 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 untill 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.

Last edited:

#### Paulanddiw

Homer Simpson Movie

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

#### Morbius

Dearly Missed
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

### Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving