Fukushima Daiichi worker Happy11311 was recently interviewed by a Japanese newspaper. Ex-SKF provides a translation of the article here.
One of the things Happy mentions is that he was outside when unit 3 exploded on March 14th at 11am. He describes being covered in black soot. The large mushroom cloud of unit 3’s explosion had a dark cast to it unlike the explosion at unit 1 or the initial part of the blast at unit 3. This of course raises questions about what was in that explosive release to make the dark soot.
As part of this Ex-SKF raises the question about the neutron detection at the plant. The original unrevised monitoring data shows a pattern that correlates to the venting of unit 2 and having a north or partially north wind. Sandia National Lab’s analysis of the events assumed the venting of the wetwell (torus) of unit 2 was not successful but the neutron spikes at the main gate start at the exact time of the second and third ventings and periodically for a few hours after show they may have been successful in at least releasing contamination to the environment.
37 minutes after the second venting of unit 2 the radiation readings for gamma at the main gate jump from single digit readings to a quadruple digit reading and then stay in triple digits from an extended time. Readings went from 5.8 uSv/h (gamma) at 9pm (March 14th) when the second venting happened to 3130 uSv/h at 9:37pm and then stays in the hundreds after this. (Our interactive unit 2 timeline can be viewed here)
A number of preceding events happen. On March 13th unit 2 goes over pressure according to our data plots but is not documented in the official timelines. There is a wet well venting attempt on the 13th in the morning but this is before the torus boils, this appears to have been successful as pressure dropped. A LOCA (loss of coolant event) is assumed to have happened the morning of the 14th. It is not clear if this is the same event as the torus boiling or something that happened at the same time. The report of the torus boiling at the same time means the torus would lose the ability to scrub contamination out of venting releases. Reactor core pressure takes a considerable drop mid day on March 14th according to the data plots. This could indicate the core breached the reactor vessel at this time. There is an assumption that the Unit 3 blast the morning of March 14th may have damaged the torus vent valve but they attempt to use it later that day. Unit 2 is wet well (torus) vented a second time at 9pm on the 14th and then a subsequent jump in gamma radiation occurs that stays elevated. A group of periodic neutron increases happen then fall off at this time. At 10:50pm (22:50 March 14th) TEPCO now documents the reactor is over design pressure. Another venting is attempted this time directly from the drywell at 12:02am. The neutron jumps continue to show up periodically after this attempt. The next morning at 6am on the 15th an explosive sound is heard coming from unit 2. This is confirmed on the data plots.
At unit 2 at around 14:00 on the 14th they assume the suppression chamber (torus) had boiled making it now ineffective for condensing steam back into water. There is also the assumption of a reactor vessel breach before the second venting. This torus boiling would mean anything dumped into the torus would not condense and would stay as steam. If the second wetwell (torus) venting was successful, the radiation in the torus from the reactor would have been released directly to the air.
The vent stack used for units 1 and 2 was later found to be extremely high in radioactivity in the 10,000 mSv/h per hour range. It has been assumed that unit 1 had caused this problem. The new connection of events may cause a rethink of that idea. Unit 2 could have been the cause of the high contamination from the venting attempts for that unit.
The gamma radiation readings at the main gate went up when unit 3 exploded the morning of the 14th. Readings were into the 260 uSv/h range at the main gate when unit 3 exploded. Readings after they vented unit 2 later that day reached 760 uSv/h and then 3130 uSv/h before dropping into the 300-400 range. The radiation jump during 2’s venting was considerably higher.
There is also the well known event at unit 2 where there was an explosive sound at 6am March 15, at 8:25am white smoke is seen from the reactor. The monitoring records show a significant radiation spike at the front gate (gamma only) beginning at 6am and leading to a reading of 11930 uSv/h by 9am that morning. This event has been assumed to be the point where the containment cap gasket for unit 2 may have failed.
Certain events that had been assumed to be part of unit 3’s aftermath may have actually been part of unit 2’s failure sequence. There has also been confusion about terminology such as “neutron ray” where there were also reports that TEPCO cited a “neutron beam” starting on March 13th. It is unclear if this was just confusion of terminology or if TEPCO did actually detect neutron beams. The creation of such would require a very specific set of events to create a beam. Neutrons were detected and documented in the monitoring reports but they also list gamma detection as “y-ray” on the reports. This odd language of “neutron ray” could have contributed to some of the confusion.
There have been reports of “fuel” or “fuel fragments” as having left the reactors during the meltdowns and blasts. Since these early reports TEPCO had not elaborated further in detail what may have been ejected from the units as some type of fuel fragments.
Certain events detected at the plant correlate to specific events at unit 2 and indicate unit 2 could be the likely cause for these changes. This does not rule out the potential for unit 3 or unit 1 or 2 to have released fuel fragments during the meltdown and explosion progression of the disaster.
Archive of TEPCO’s original monitoring data
Radiation maps of the plant from 2013
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