When the test was started, a series of events caused the operators to block off essential safety systems. They then were gradually boxed in as a result. Eventually when they realised that an uncontrolled increase in power was imminent it was too late for the reactor to be shut down, even though a full emergency shutdown procedure had by then been initiated.
For the third time we were treated to a rehearsal of the accident sequence and some details which do not appear in the report were given.
1.
The description given was as follows:
The control and safety rods had been withdrawn from the core to compensate for xenon poisoning.
2.
All 8 main circulating pumps were in operation. They were circulating hot water which was everywhere near to boiling although little steam was being generated.
3. When the main circulation pumps began to run down (due to run-down of the turbo-alternator) flow was reduced, the water boiled and there was a consequent uncontrollable increase in power.
4.
Steam pressure destroyed the core and the upper structure
of the reactor.
Calculations indicate that the power increased by a factor of 100 in less than 1 second, a release of energy which disrupted the fuel into small particles at 3000°C. These converted the remaining water droplets to steam which blew off the reactor cap and destroyed the building. Three to four seconds later according to witnesses outside the building a second explosion occurred. It was probably due to the detonation of hydrogen or carbon monoxide.
Hot burning debris caused subsidiary fires which were put out although many of the fire fighters later died.
Session 2B, 10.00 to 18.00 hours: Detailed Presentations of Emergency Measures and Radiological Consequences
Evacuation, environmental protective actions, decontamination, environmental effects, health effects.
The Working Group session was opened by Prof. L A Ilyin (Academy of Medical Sciences, Director of the Institute of Biophysics) who outlined the affiliations and specialisms of the speakers to follow and set their contributions in context. Ilyin gave the following time-table of events with respect to medical response:-
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