Comment by sehansen
4 hours ago
I can't find any description of the test across the three reports mentioning that that emergency stop button is supposed to be pressed as part of the test. AFAICT the test wasn't even completed when the button was pressed as the purpose of the test was to demonstrate that the emergency core cooling system could run for at least 40 s (INSAG-1 page 17) after closing the turbine emergency stop valve. That valve was closed at 01:23:04 and AZ-5 was pressed at 01:23:40.
For the rundown test, after the valve cut-off, it is irrelevant whether the reactor was shut down or not. The working plan for the test only specified that it was supposed to run before a planned maintenance period, so the shutdown was implied. During previous tests, the AZ-5 signal was wired to the valve cut-off signal and was sent automatically at the same moment. It is not clear why this changed in 1986, but the outcome would have been the same if AZ-5 had been pressed 35 seconds earlier.