a reply to: Bluntone22
I'm not so sure it can be that black and white ie wiki page on chernobyl explosions :
As the scram was starting, the reactor output jumped to around 30,000 MW thermal, ten times its normal operational output, the indicated last reading
on the power meter on the control panel. Some estimate the power spike may have gone ten times higher than that. It was not possible to reconstruct
the precise sequence of the processes that led to the destruction of the reactor and the power unit building, but a steam explosion, like the
explosion of a steam boiler from excess vapour pressure, appears to have been the next event. There is a general understanding that it was explosive
steam pressure from the damaged fuel channels escaping into the reactor's exterior cooling structure that caused the explosion that destroyed the
reactor casing, tearing off and blasting the upper plate, to which the entire reactor assembly is fastened, through the roof of the reactor building.
This is believed to be the first explosion that many heard.:366
This explosion ruptured further fuel channels, as well as severing most of the coolant lines feeding the reactor chamber, and as a result, the
remaining coolant flashed to steam and escaped the reactor core. The total water loss in combination with a high positive void coefficient further
increased the reactor's thermal power.
A second, more powerful explosion occurred about two or three seconds after the first; this explosion dispersed the damaged core and effectively
terminated the nuclear chain reaction. This explosion also compromised more of the reactor containment vessel and ejected hot lumps of graphite
moderator. The ejected graphite and the demolished channels still in the remains of the reactor vessel caught fire on exposure to air, greatly
contributing to the spread of radioactive fallout and the contamination of outlying areas.[d]
According to observers outside Unit 4, burning lumps of material and sparks shot into the air above the reactor. Some of them fell onto the roof of
the machine hall and started a fire. About 25 percent of the red-hot graphite blocks and overheated material from the fuel channels was ejected. Parts
of the graphite blocks and fuel channels were out of the reactor building. As a result of the damage to the building an airflow through the core was
established by the high temperature of the core. The air ignited the hot graphite and started a graphite fire.:32
After the larger explosion, a number of employees at the power station went outside to get a clearer view of the extent of the damage. One such
survivor, Alexander Yuvchenko, recounts that once he stepped outside and looked up towards the reactor hall, he saw a "very beautiful" laser-like beam
of blue light caused by the ionized-air glow that appeared to "flood up into infinity".
There were initially several hypotheses about the nature of the second explosion. One view was that the second explosion was caused by the combustion
of hydrogen, which had been produced either by the overheated steam-zirconium reaction or by the reaction of red-hot graphite with steam that produced
hydrogen and carbon monoxide. Another hypothesis, by Checherov, published in 1998, was that the second explosion was a thermal explosion of the
reactor as a result of the uncontrollable escape of fast neutrons caused by the complete water loss in the reactor core. A third hypothesis was
that the second explosion was another steam explosion. According to this version, the first explosion was a more minor steam explosion in the
circulating loop, causing a loss of coolant flow and pressure that in turn caused the water still in the core to flash to steam; this second explosion
then caused the majority of the damage to the reactor and containment building.
Other explosion hypotheses
The force of the second explosion and the ratio of xenon radioisotopes released after the accident (a vital tool in nuclear forensics) indicated to
Yuri V. Dubasov in a 2009 publication (suggested before him by Checherov in 1998), that the second explosion could have been a nuclear power transient
resulting from core material melting in the absence of its water coolant and moderator. Dubasov argues that the reactor did not simply undergo a
runaway delayed-supercritical exponential increase in power into the multi-gigawatt power range. That permitted a dangerous "positive feedback"
runaway condition, given the lack of passive nuclear safety stops, such as Doppler broadening, when power levels began to increase above the
The evidence for this hypothesis originates at Cherepovets, Vologda Oblast, Russia, 1000 km northeast of Chernobyl. Physicists from the V.G. Khlopin
Radium Institute in Leningrad measured anomalous xenon-135 — a short half-life isotope — levels at Cherepovets four days after the explosion, even
as the general distribution was spreading the radiation to the north in Scandinavia. It is thought that a nuclear event in the reactor may have raised
xenon to higher levels in the atmosphere than the later fire did, which moved the xenon to that location.
That while this positive-feedback power excursion that increased until the reactor disassembled itself by means of its internal energy and external
steam explosions is the more accepted explanation for the cause of the explosions, Dubasov argues instead that a runaway prompt criticality
occurred, with the internal physics being more similar to the explosion of a fizzled nuclear weapon, and that this failed/fizzle event produced the
This nuclear fizzle hypothesis, then mostly defended by Dubasov, was examined further in 2017 by retired physicist Lars-Erik De Geer in an analysis
that puts the hypothesized fizzle event as the more probable cause of the first explosion. The more energetic second explosion, which
produced the majority of the damage, has been estimated by Dubasov in 2009 as equivalent to 40 billion joules of energy, the equivalent of about ten
tons of TNT. Both the 2009 and 2017 analyses argue that the nuclear fizzle event, whether producing the second or first explosion, consisted of a
prompt chain reaction (as opposed to the consensus delayed neutron mediated chain-reaction) that was limited to a small portion of the reactor core,
since expected self-disassembly occurs rapidly in fizzle events.
Lars-Eric De Geer comments:
"We believe that thermal neutron mediated nuclear explosions at the bottom of a number of fuel channels in the reactor caused a jet of debris to shoot
upwards through the refuelling tubes. This jet then rammed the tubes' 350kg plugs, continued through the roof and travelled into the atmosphere to
altitudes of 2.5-3km where the weather conditions provided a route to Cherepovets. The steam explosion which ruptured the reactor vessel occurred some
2.7 seconds later."
Look for the Fukushima or Kitahara plant on google earth , without using the search bar - it's not there . But Use the search bar - it takes you to
get some 2011 images