Chernobyl Sky Atlantic.

[HaiKarate]

One word. Brilliant. The Soviet officials stating that the radiation reading was 3.6 Roentgen when in fact it was 20,000.

[Cyder]

There's a fascinating thread in the TV section if you haven't seen it with lots of input from guys in the industry including llewop who worked on the new building (NSC?).

[HaiKarate]

Thank you. I’ll take a look. Thought it would be here to be honest where all the nuclear physicist types hang out.

[PRTVR]

HaiKarate said:

One word. Brilliant. The Soviet officials stating that the radiation reading was 3.6 Roentgen when in fact it was 20,000.

Have to agree, was not sure if it was my thing but absolutely love it, they were correct in the reading, that was the max reading for one of the instruments.

[Cyder]

No probs, I think they've escaped across the border into the TV section, they'll be back once the PH hamsters have rounded them up.

[HaiKarate]

Indeed. It will be good to get a detailed (non cluttered) analysis of the actual incident over here. I remember it well as I’d recently been posted to West Berlin straight out of Army training. I was based next door to Spandau Prison which, at the time, housed Rudolph Hess. Crazy times.

[llewop]

Cyder said:

No probs, I think they've escaped across the border into the TV section, they'll be back once the PH hamsters have rounded them up.

It did cross my mind about a thread here for discussion of technical stuff, but once it started in the TV section thread..... and as ever meandered off topic in all sorts of radiation related directions …. took on a life of its own!

and yes: NSC = New Safe Confinement


I'll get back in my box now … my wife would say that should have happened years ago, but then she did also follow me out to Slavutich (Pripiyat V2 in a way... the replacement town for the workers) and loved it out there.

[ElectricSoup]

HaiKarate said:

Indeed. It will be good to get a detailed (non cluttered) analysis of the actual incident over here. I remember it well as I’d recently been posted to West Berlin straight out of Army training. I was based next door to Spandau Prison which, at the time, housed Rudolph Hess. Crazy times.

I went past there as a 14 year old on a school trip one evening, on the U-Bahn (or was it S-Bahn in the West?). There was one light on in the whole building. Must have been Hess's cell window. *shiver*

[HaiKarate]

ElectricSoup said:

I went past there as a 14 year old on a school trip one evening, on the U-Bahn (or was it S-Bahn in the West?). There was one light on in the whole building. Must have been Hess's cell window. *shiver*

S Bahn for Buses and U Bahn for underground. It was great for soldiers as transport was free of charge if in uniform.

[anonymous-user]

I've just read a couple of very good books on Nuclear accidents, which if you are interested in the details and technicalities are excellent!

Chernobyl: History of a Tragedy
by Serhii Plokhy







Atomic Accidents: A History of Nuclear Meltdowns and Disasters: From the Ozark Mountains to Fukushima Paperback
by James Mahaffey






Both are very good indeed, but the Atomic Accidents book is incredible detailed, and written by someone who worked in the industry and has an innate understanding of nuclear physics. In fact, in a few places i was left wondering if he was actually revealing classified info due to the fine detail and explanations of these events!

[llewop]

Max_Torque said:

Both are very good indeed, but the Atomic Accidents book is incredible detailed, and written by someone who worked in the industry and has an innate understanding of nuclear physics. In fact, in a few places i was left wondering if he was actually revealing classified info due to the fine detail and explanations of these events!

Possibly/probably not - there can be an amazing amount of information available on incidents, once the dust settles or even before;

I re-found something today that I'd seen a long time ago regarding the criticality accident at Tokaimura in Japan.

extract said:

We would much appreciate it if you could provide us the following information AS SOON AS POSSIBLE:
(1) The possible way to stop the recriticality. Uranium with liquid acid may be still in the tank without any
control device.
(2) Any suggestion on the evacuation. The current reaction may be too overestimated.
(3) Other useful information

which was part of a message on a forum for radiation safety. It seemed to be saying 'we don't know how to stop it'!!

[Lazadude]

My question got buried on the TV forum, wondering if the scientific part may answer.

I know the accident was through lack of knowledge (either training or removed by the KGB), but with what we know now - Would it have been possible to save the reactor before they scrammed/AZ5'd it?

Power the water up and Introduce the rods 1 at a time for example? Or would the reactor have heated too fast once it burnt off the Xe131?

[llewop]

Lazadude said:

My question got buried on the TV forum, wondering if the scientific part may answer.

I know the accident was through lack of knowledge (either training or removed by the KGB), but with what we know now - Would it have been possible to save the reactor before they scrammed/AZ5'd it?

Power the water up and Introduce the rods 1 at a time for example? Or would the reactor have heated too fast once it burnt off the Xe131?

I’m sure it would have been possible. I’m not a current or former reactor operator, but would have thought that the other way out would have been something like starting the pumps to circulate the water but also waiting out the decay of the poisons. But that would have taken time and ended the test as a fail.

Or something like that.....

[McGee_22]

llewop said:

Lazadude said:

My question got buried on the TV forum, wondering if the scientific part may answer.

I know the accident was through lack of knowledge (either training or removed by the KGB), but with what we know now - Would it have been possible to save the reactor before they scrammed/AZ5'd it?

Power the water up and Introduce the rods 1 at a time for example? Or would the reactor have heated too fast once it burnt off the Xe131?

I’m sure it would have been possible. I’m not a current or former reactor operator, but would have thought that the other way out would have been something like starting the pumps to circulate the water but also waiting out the decay of the poisons. But that would have taken time and ended the test as a fail.

Or something like that.....

It's pretty difficult to say when the point of no return/inevitable accident was reached without knowing all the plant parameters at the time.

RBMK's have what I know as a positive coefficient of reactivity; that is, if thermal heat is introduced into the core, the reactivity (neutron levels) will increase, so conversely if cold water is introduced then (hopefully) neutron levels will decrease. This sounds the safe way round but really isn't as increasing reactor power gives off thermal power which increases neutron levels which increases reactor power and so on, basically it runs away with itself.

I operated Naval Pressurised Water Reactors which had a negative coefficient of reactivity so as the reactor got thermally hotter the reactivity would decrease effectively lowering the power level of the core; one of the few risks with a negative coefficient reactor is the introduction of cold(er) (the actual figures are all relative to the nominal reactor operating temperature) water into the reactor which would increase reactivity.

The biggest problem the operators faced was the fact that they had withdrawn lots of the manually operated control rods in order to overcome the xenon poisoning; once the reactor power levels became unstable following this phase is perhaps when lots of thinking should have occured as to, 'what if something goes wrong now?'.

Again with huge hindsight, they should have considered how much, or little, control they had over neutron levels with just the very few automatic control rods there are on a RBMK, as well as how much cooling water they could possibly provide should reactor power start increasing.

Perhaps because of the pressure exerted by Diatolov to get the test done there didn't seem to a point at which the plant operators were allowed to take stock of their actual situation and perhaps plan ahead; this, added to the unreleased information that the graphite tipped automatic control rods actually locally significantly increased reactivity in the core are the key points for me as a previous operator.

I can recall from my own days the expression 'RILF' and 'ROLF' and following a reactor scram and poison build up the slow control rod extraction to restart and increase reactor power was almost inevitably followed by a period of 'Rodding In Like F***' to maintain control over the reactor.

The physical structure of an RBMK did not allow for 'RILF'ing in quite such dynamic circumstances as other reactor designs so once the unstable power levels had started to unpredicatably increase with no forethought as to how to deal with them they had only a small number of (design flawed) automatic control rods and what appeared to be an insufficient reserve of cold water to try and cut back the increasing power levels.

With all that in mind I think the point of no return was reached once they started to withdraw more control rods in order to overcome the power dip caused by the xenon poisoning. This attempt to increase power on an unstable reactor with a diminishing amount of control facility available set the cogs in motion for an reactor accident of some degree.

I say 'some degree' because once again it is unknown from any of the unreliable readings they were obtaining just how close they were to being able to 'just' shut down the reactor, or 'just' have the accident they did, instead of one which, if circumstances prior to the accident had been ever so slightly different, could have made the accident even worse.

There is a lot of supposition in there, as there always can be be in 'what if' situations. If I have made some errors just bear in mind its twenty years or more since I last RILFed and ROLFed with the knob on the panel.

Hth.

[HaiKarate]

Thanks for your explanation. Makes sense. Well kind of. Lol. I only wish I’d tried harder at school.

[FarmyardPants]

Max_Torque said:

I've just read a couple of very good books on Nuclear accidents, which if you are interested in the details and technicalities are excellent!

Chernobyl: History of a Tragedy
by Serhii Plokhy








Atomic Accidents: A History of Nuclear Meltdowns and Disasters: From the Ozark Mountains to Fukushima Paperback
by James Mahaffey






Both are very good indeed, but the Atomic Accidents book is incredible detailed, and written by someone who worked in the industry and has an innate understanding of nuclear physics. In fact, in a few places i was left wondering if he was actually revealing classified info due to the fine detail and explanations of these events!

Just popped in to say thanks for the recommendations, have bought the kindle version of the Atomic Accidents book, enjoying it so far and I love reading about this stuff, I find it fascinating.

[Krikkit]

McGee_22 said:

*lots of interesting stuff*

Thanks, interesting to hear from someone who has actually operated a reactor!

As a physics graduate and somewhat of a nerd around the subject I think they reached the point of no return when they ended up at <10% and decided to raise the power quickly, because they inevitably had to pull far too many rods out to be able to maintain even the slightest control...

They might have been able to avoid it if they had a different set of rules in place about how to handle the reactor once it had passed below 10% thermal design level; that was where a lot of the instrumentation and control systems stopped working, so they should have had an immutable framework of rules in place, regardless of how you ended up there, but the rule book apparently had quite a few qualifiers of where the start point was.

ETA: I dug out this site which might be quite interesting - a bunch of graphs from the SKALA about the conditions in the minutes before the accident. http://accidont.ru/ENG/data01.html

Edited by Krikkit on Wednesday 19th June 12:00