What's the "Control System Tank" in RBMK

[Reuenthal]

In the HBO TV show Chernobyl, deputy chief engineer Anatoly Dyatlov said Control System Tank， Hydrogen...
What's the control system tank in RBMK?

 

[Reuenthal]

Is it annual water tank in the reactor ?

 

[Astronuc]

Is it annual water tank in the reactor ?

It's not clear from readily available diagrams in English.

I found some schematics from the Lithuanian Energy Institute and the International Nuclear Safety Center based on Ignalina. The diagrams are not necessarily complete or explicit. They do reference the annual water tank, but as part of the radial biological shielding. http://www.lei.lt/insc/handbook/hab1/hab13.html
http://www.lei.lt/insc/handbook/part1.pdf

I found a chapter of Design Basis Accidents
http://www.lei.lt/insc/handbook/part23.pdf

While there is a reference to Accident Containment System, there is no explicit reference to a Control System Tank, so it is not clear to what the HBO documentary is referring. Yet Control System Tank is mentioned:

There's a fire in the turbine hall.
The turbine hall.
The control system tank. Hydrogen.
You and Toptunov, you
morons blew the tank!
- No, that's not
- This is an emergency.
Everyone stay calm.

Then later
The tank, it's big enough.
This kind of explosion, the control
tank on 71, it's 100 cubic meters.
One hundred and ten.
Hundred and ten. It
could do this, definitely.
It's gone.
I looked right into it.

Read more: https://www.springfieldspringfield....pts.php?tv-show=chernobyl-2019&episode=s01e01

It's difficult to understand, but the reference to the Control System Tank is in the turbine hall, but the context is not clear, although it would suggest some kind of safety injection tank, perhaps with borated water.

 

[Astronuc]

In Appendix 2 ofhttp://www.lei.lt/insc/handbook/append.pdf, there is an emergency water tank (9), which is connected to a coolant tank (7), so perhaps (9) is what they HBO program refers to as the control system tank. Again, it's not clear given limited information.

 

[Rive]

The turbine hall.
The control system tank. Hydrogen.

Based on the text only maybe the hydrogen reserves for generator cooling? Those generators had hydrogen as coolant for the rotors.

PS.: according to the actual timeline instead, after the explosion Dyatlov believed that accumulated hydrogen blew up in a not-so-well specified 'the emergency tank of the safety control system'. That 'safety control system' part was mentioned as 'protection and control system' in a different source.
Dyatlov that time was shocked and possibly (not exactly clear) got his half-deadly dose already. The historical accuracy might be good, but the actual words not necessarily makes sense.

 

[artis]

As much as I remember from real biographies not HBO shows, Dyatlov indeed got a radiation dose that night of the accident which was considered close to lethal , he later in an interview said that by the morning hours he was feeling drunk and exhausted and he was driven home to get some sleep. It was kind of funny because the way he said it made it sound like it was no big deal for him.
In fact Anatoly Dyatlov lived another 9 years after the accident and died in 1995, at the age of 64, he was smoking heavily, and Chernobyl wasn't the only plant where he had gotten a severe radiation dose, many years before he was working as a young engineer in one of Soviet nuclear submarine repair bases where he worked with the submarine nuclear reactors, apparently some accident happened and he got about 200rem.
As for the tank question, as much as I know over the years, RBMK 1000 had two 500MW generator sets for each reactor and they were hydrogen cooled, so apparently there was hydrogen stored in or near the turbine hall.
under the reactor where all the countless input water pipes are attached and then they morph into the vertical fuel channels is a large basement room hermetically shielded and partly filled with water, the idea is I understand it is in case one or two fuel channels break the radioactive steam bubbles through the water and any gasses exiting from the water can be filtered through ventilation.
This is the tank they tried to drain because the molten fuel was slowly approaching the tank, and they feared a steam explosion might happen.
This is where the speculation comes in as apparently some believed there could also be a nuclear explosion once the molten fuel reaches the water.

 

[Astronuc]

There is an account in this document: https://apps.dtic.mil/dtic/tr/fulltext/u2/a335076.pdf

Starting on page 8 of the document (page 10 of pdf), the author talks about traveling to Pripyat and Chernobyl. The author had been at Chernobyl assessing the progress of Unit 5 construction.

In the Appendix 2 of the handbook I cited above, between 7 and 9 there is 8, the CPS cooling system pump. CPS is part of the Control and Protection System, so one of those tanks, perhaps 9, is the control system tank. Hydrogen could be generated by reaction of the water with zirconium in the fuel cladding and possibly the pressure tubes, or by radiolysis of the coolant if the neutron and gamma radiation is sufficiently high and the coolant is more or less stagnant.