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Comment by sehansen

4 hours ago

How does it make sense that the show ignores INSAG-7 when the whole plot point about the design of the control rods increasing the reactivity isn't from INSAG-1 but from INSAG-7? The same with the plotline about this defect being known, but kept from the operators. And Legasov lying about all this at the IAEA meeting? All-in-all INSAG-1 paints a picture of operator failure, INSAG-7 paints a picture of systemic failure and the show paints a picture of systemic failure.

And to nitpick: INSAG-7 doesn't disagree with INSAG-1 about the power rising just before AZ-5. From page 8 of INSAG-7: "When the turbine was tripped, the four pumps it was powering began to slow down as the turbine speed was reduced and the associated generator voltage fell. This reduced rate of core flow caused the void content of the core to rise and caused an initial positive feedback of reactivity which was at least in part the cause of the acci- dent." (page 8) This happens ~30 seconds before AZ-5 is pushed.

The same event described in Table I on page 21-22 of INSAG-1, with the part deprecated by INSAG-7 marked with {}:

01:23:04 {The personnel blocked the two-TG trip signal.} Emergency stop valve to the turbine was closed. The reactor continues operating at a power of 200 MW(th).

01:23:10 One group of automatic control rods start driving out

01:23:21 Two groups of automatic control rods begin reinsertion.

01:23:31 Net reactivity increasing with subsequent slow increase in reactor power.

01:23:40 Operator pushes AZ-5 button (reactor trip).

The textual description on page 25 of INSAG-1 isn't much different: "When the emergency stop valve to the turbine was closed, the steam pressure began to rise. The flow through the core started to drop because four of the main cooling pumps were running down with the generator. Increasing pressure, reduced feedwater flow and reduced flow through the reactor are competing factors which determine the volumetric steam quality and hence the power of the reactor. It should be emphasized that the reactor was then in such a state that small changes in power would have led to much larger changes in steam void, with consequent power increases. The combination of these factors ultimately led to a power increase begninning at about 01:23:30."

A scanned copy of INSAG-1: https://ilankelman.org/miscellany/chernobyl.pdf

The Soviet report to IAEA in 1986: https://inis.iaea.org/collection/NCLCollectionStore/_Public/...

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sehansen

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man8alexd  3 hours ago

Quote from INSAG-7 https://www-pub.iaea.org/MTCD/Publications/PDF/Pub913e_web.p...

> neither the reactor power nor the other parameters (pressure and water level in the steam separator drums, coolant and feedwater flow rates, etc.) required any intervention by the personnel or by the engineered safety features from the beginning of the tests until the EPS-5 button was pressed. The Commission did not detect any events or dynamic processes, such as hidden reactor runaway, which could have been the event which initiated the accident. “

  • sehansen  3 hours ago

    Sure, I'm just saying the power increase did happen, according to both INSAG-1 and INSAG-7. Neither INSAG-1, INSAG-7 nor Legasovs report claims there is a rapid increase in power before AZ-5 is pushed. The claim in INSAG-1 is that this power increase was the start of a positive-feedback loop that caused the explosion. The claim in INSAG-7 was that the power increase was not a safety problem, except to the extent it caused the operator to push AZ-5.