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 Third page of a chronology from a Department of Energy report

Chernobyl Disaster timeline, third page of a chronology from a Department of Energy report

Chernobyl Disaster timeline, third page of a chronology from a Department of Energy report

Time:0122:30 Power: 200 MWt

Operator noted reactivity to reserve was about 6-8 rods as opposed to the to the normal of 30 rods. Far below the value where reactor shutdown is required. No action taken.  A printout of the actual core flux monitor outputs and the position of all the regulating rods was obtained at this time ("Skala" system). The axial flux double peaked with the higher peak in the top section of the core.

Time: 0123:04 Power: 200 MWt

Steam flow valve to TG #8 was closed to begin test. The signal for reactor shutdown on closure of both turbogenerator steam valves had been disengaged in order to allow repeating the test if needed. This was in violation of the test program and normal operating procedures. 

Flow rate began to fall as the 4 main cooling pumps powered by TG #8 began to run down. Steam pressures also began to increase due to removal of TG steam load and the reduction (by operator action) of the feedwater rate about 1 minute before. All these factors lead to an increase in the coolant void fraction (positive reactivity insertion) and a resulting power increase. 

Due to the reactor conditions at the time of the test, the void fraction increased many times more sharply than at normal power. (Also the void reactivity coefficient was at a higher value than at normal operating conditions.)

Power:530 MWt and

Power began to increase. After 3 seconds it was 530 MWt and the increasing "runaway period came to be much less than 20 seconds."  The positive void coefficient "promoted deterioration of the situation." Only the Doppler effect partially compensated for the void reactivity increase. Water flow continued to decrease (due to run
 

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