How Accurate is HBO's Chernobyl in Explaining Nuclear Reactor Physics?

[artis]

@franklyamazed I don't think I can agree with your postulate that "graphite is less a moderator than water"

https://energyeducation.ca/encyclopedia/Neutron_moderator

See the table for scattering and neutron absorption, water is a good moderator but it absorbs neutrons far more than graphite so from the two graphite is more efficient from a neutron perspective.
So when the rods were lowered into the RBMK in fact what happened is the less efficient water moderator was replaced with a more efficient graphite one which lead to the additional increase in reactivity. This is the reason why the blast happened right after the SCRAM was initiated.

Also the reason why CANDU reactors use heavy water is because ordinary light water has a lesser neutron economy compared to heavy water.
All in all graphite vs water in the same situation with all being identical , graphite will produce a larger reactivity increase simply because it will allow for more neutrons to do their job, at least that is what I get from all the tables and literature.

 

[gmax137]

maybe someone in the net has given a summary which part of the series is true facts and false physics?

Here's a new one:
http://ansnuclearcafe.org/2019/07/10/how-hbo-got-it-wrong-on-chernobyl/#sthash.6aUDsgNo.dpbs

 

[GTOM]

Sorry if it isn't the most proper thread for this (in this case, i would be glad for a link), but i wondered about the scene when robot circuits fryed due to gamma radiation, so they sent biorobots to clean the roof...
Any data about their fate, how could their cells handle so intense radiation? As far as i know, the worst effect is swallow the radioactive dust (people who did this, almost surely died) and unstable iodide takes place in the body. Gamma radiation itself has a much less worse effect on organic bodies?

Does present day robots handle much better such a situation? As far as i know, the ones sent to Fukushima also melt down.

 

[artis]

Gamma is nothing more than very energetic photons or very high energy EM radiation. Since the particles that carry the EM radiation have no mass and no electrical charge they can penetrate very far into a material, unlike alpha or beta which have both mass and charge.

I don't have any data here about the doses of liquidators and I doubt someone here does but this is not so straight forward as you would think, I would even say measuring doses and understanding the effects of radiation to biological bodies is the hardest part of nuclear physics. Swallowing or taking in with air small radioactive particles is not necessarily the end much like being in a gamma background isn't it all depends on the amount of dose absorbed and the time period that it took. This is the reason the guys were up on the roof for only 2 minutes max.
I think breathing in a few hundred radioactive particles does nothing much to ones body on average as I am sure most of the cleanup guys in Chernobyl did just that as it was summer and respirators were rarely used.
Now breathing or drinking in a whole lot of radioactive substances causes acute radiation sickness and death , see Alexander Litvinenko, the Russian KGB spy who decided that he will dare to open his mouth about his former work place, they poisoned him with a small amount of Polonium 210 which emits alpha radiation, they added the substance to his tea , a single cup was enough to kill him in two painful weeks.i am not an expert on radiation doses etc so I can only say the overall picture, just remember your body is nothing more than a sack of cells that are made from atoms just like any other thing you are surrounded. Whether radiation will cause cancer or death solely depends on how many of the total amount of cells are destroyed in your body and where. Cells die all the time and new ones get created by the body as long as you don't kill too many you are fine , eating and sleeping recovers the body.
The supervisor at the reactor 4 at the night of the accident Anatoly Dyatlov received what is estimated to be a lethal dose that night , at morning he was vomiting, feeling sick and loosing his thinking he was taken to hospital , he recovered and lived almost another 10 years until he died a little over 60 years old (63 I think) so no one can say for certain , different people perform differently under severe circumstances.

 

[artis]

Oh one more thing, the same Dyatlov that I mentioned in my previous post was a chainsmoker for most of his life, he smoked something like 1 to 2 packs of cigarettes a day and he did not die from cancer but from heart failure, surely his almost lethal dose at Chernobyl probably contributed to his death at 63 but it could also very well be the case that his unhealthy lifestyle, stress and nonstop smoking of red labeled cigarettes caused his early demise.
I just want to point out that it is really complicated to determine what will happen to a person after a certain dose of ionizing radiation, unless the dose is lethal or close to that it might well be that the person is fine and maybe only minor injuries result like pain in joints, more frequent headaches and some other otherwise minor symptoms that are reported by the surviving liquidators. It is a myth that all of them have died or suffered from classic cancers.
Surely there is an increased cancer rate among the liquidators as well as on average they look and feel older than their physical age. The same happens with alcoholics, basically any long term abuse of health results in the body wearing out faster. I know this because plenty of men went to Chernobyl from my country and over the years I have read about their stories and medical records. Some I knew personally.

 

[GTOM]

So the test they made actually wanted to improve security, to deal with the consequences of a power shortage.

I wonder how could a present day nuclear power plant deal with such a situation?
It is good that my country has PWR type reactor with negative void coefficient.

 

[artis]

Yes the test was meant to determine whether the turbine inertia is enough in order to power the core cooling pumps at reactor shutdown power levels for the time needed before backup diesels were capable of producing the required power.
In older RBMK reactors this time span was roughly 1 minute, it was so long due to the diesels. In modern reactors and modern emergency power systems this time is much much shorter.

The test in itself wasn't dangerous , the way in which it was carried out and the reactor type on which it was carried out was what made all the difference and history.

 

[gmax137]

I wonder how could a present day nuclear power plant deal with such a situation?

Modern "passive" designs such as Westinghouse AP1000 do not rely on AC-electric motor driven equipment (big pumps) to maintain core cooling and heat removal. Operation of the diesel generators in these designs is therefore not required to prevent core damage.

 

[willem2]

So the test they made actually wanted to improve security, to deal with the consequences of a power shortage.

I wonder how could a present day nuclear power plant deal with such a situation?
It is good that my country has PWR type reactor with negative void coefficient.

There are a lot of emergency cooling systems that can work on battery power, or passive cooling
https://en.wikipedia.org/wiki/Boiling_water_reactor_safety_systems
They generally need either battery power or a cold water storage. Both can run out, but not until long after the turbines would spin down in an RBMK.