Two Important Mysteries Remain Unresolved
On
August 27 of this year, I sent a letter of
request titled “Regarding continuation of the investigation into causes
of the accident at the Fukushima Daiichi Nuclear Power Station of the
Tokyo Electric Power Company, and execution of the on-site inspection
by the Diet centered on the 4th floor of the Unit 1 reactor building
(request)” by fax and mail to Bunmei Ibuki, Speaker of the House of
Representatives, and Masaaki Yamazaki, Chair of the House of
Councillors. In addition, I held a press conference at the Diet Office
Building with attorney Yoshinori Ito, who had, as a cooperative member
of NAIIC, worked with me for half a year in the same NAIIC working
group.
In fact, on February 7 of this
year, Mr. Ito and I
sent letters to the then speakers of both houses, requesting the Diet
to conduct the on-site investigation of the 4th floor of the Unit 1
reactor building of Fukushima Daiichi Nuclear Power Station (FDNPS).
This was because we knew that TEPCO had stonewalled the very
investigation NAIIC was planning to perform.
However, even though we have requested an on-site
inspection of the 4th floor of the Unit 1 building twice within a half
year, there has been no response from the Diet, nor has the inspection
been conducted.
One
year has already passed since the Diet’s
investigation into the accident was dissolved, but there is now more
reason than ever, of course, for our sticking to the 4th floor of
the Unit 1 building. It appears there is a possibility that the
prolonged violent seismic motion due to the earthquake (March 11, 2011)
damaged the emergency isolation condenser (IC) pipes located in the 4th
floor, causing a small-break LOCA (loss-of-coolant accident). The
issues we are being particular about are not limited to that, however.
There
is one more major item. That is the matter of whether or not it was
really the tsunami that caused the so-called “Station Blackout” (SBO:
loss of all AC power to a nuclear plant). In fact, the results of the
most recent detailed investigation and analysis by Mr. Ito into Unit 1,
in particular, lend strong credence to arguments that the cause
of the SBO was “something else,” and not the tsunami.
The September issue of the monthly Science Journal
Kagaku (Iwanami Shoten, Publishers), released on August 26, carried Mr.
Ito’s disquisition on the connection between the tsunami and SBO
(1), and my own disquisition
(2)
on the 4th floor of the Unit 1 building. These two disquisitions
constitute “our current thoughts” on the above-mentioned unresolved
issues. On the basis of these two disquisitions, as stated above, on
the next day (August 27), we made a request to the speakers of both
houses for an on-site inspection of the 4th floor of the Unit 1
building as a continuation of the NAIIC investigation.
In an explanation and discussion of the SBO problem
by Mr. Ito himself, broadcast live over the Internet by CNIC, he gave
the view that the SBO at “Fukushima Daiichi Nuclear Power Station Unit
1 was not caused by the tsunami.”
(3) Due to limited space, I
cannot include the details here, but regarding the above-mentioned
“something else,” a former GE nuclear engineer by the name of Satoshi
Sato has an interesting hypothesis, in relation to which, important
questions are posed regarding the new regulatory requirements.
Thus, in order to reflect the latest dispute
regarding the tsunami and SBO, I will present my own hypothesis below
on what occurred on the 4th floor or the Unit 1 building.
(4)
Water Leakage Phenomena and the Possibility of an SR Valve Non-function
The NAIIC report
(5) does not mention the
possibility that the IC pipes may have broken due to seismic motion or
that a loss-of-coolant accident (LOCA) may have occurred. Personally,
however, during the NAIIC investigation, I was thinking that there had
been a small-break LOCA with small cracks developing in the piping
directly connected to the IC units on the 4th floor of the reactor
building due to the prolonged violent seismic motion, which continued
for several minutes, causing reactor coolant to shoot out from them
(and basically, my thoughts on this have not changed). In fact, there
were at least two events at the scene that would lead one to think that
way.
The first is that “water leakage phenomena,” with
water suddenly gushing out from somewhere, did occur right after the
earthquake on the 4th floor of the Unit 1 building, where the IC units
were located. This leakage was witnessed by several employees who
happened to be working on the 4th floor at that time.
The second is that there is no evidence whatsoever
that the main steam release safety valves (SR valves) functioned—i.e.,
it is possible that they didn't work at all. An SR valve is a device
for reducing pressure in a nuclear reactor by releasing steam,
automatically or by manual operation, from within the reactor to the
outside, but particularly in the case of the Mark I type containment
vessel used in FDNPS Units 1 to 5, which has a doughnut-shaped pressure
suppression chamber, when an SR valve operates, “hydraulic dynamic
loading,” a large dynamic force, is known to occur in the pressure
suppression chamber, and I imagine that it would produce a violent
vibratory noise in the chamber. In fact, in Units 2 and 3, SR valves
began functioning frequently about ten minutes after the earthquake,
and when they did, it sounded like the earth rumbling, audible as far
away as the Central Control Room, as was learned from the testimony of
several operators.
We also learned from a questionnaire survey
conducted by the NAIIC that noise from the operation of SR valves could
be heard at Onagawa NPS Units 1 and 3, which have an improved version
of the same Mark I containment model (Unit 2 was off-line for periodic
inspections).
In the case of FDNPS Unit 1, however, we learned
from interview surveys with the workers during the NAIIC investigation
that not one person among the workers heard the sound that an operating
SR valve would have made. In the case of Unit 1, SR valves would
normally have been operating repeatedly right after a tsunami, but
nobody heard the sound that would have accompanied them. The hypothesis
that perhaps by chance they couldn’t hear them because they were drowned out
by other noise nearby does not stand up to scrutiny. The plant suffered
a complete loss of electrical power after the tsunami hit, and the
workers testified that Unit 1 was engulfed in darkness and silence.
If any of the SR valves of Unit 1 were not
functioning, it indicates that one pipe or another into or from the
reactor (e.g., an IC pipe) had been damaged by the earthquake jolts,
and the coolant leaking from it reduced the pressure so that the
pressure inside the reactor never rose as high as would be expected,
and one could surmise that as a result the SR valves did not function.
The water leakage phenomena and possible
non-functioning, or lack of necessity to function, of the SR valves by
themselves, however, do not provide enough evidence to lead inevitably
to the conclusion that a small-break LOCA might have occurred in the IC
pipes due to seismic motion. More direct evidence or further proof is
needed to draw such a conclusion.
|
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Fig. 1
Fourth floor plan of Fukushima Daiichi NPP Unit 1 reactor building
(prepared by the Citizens’ Nuclear Information Center, based on figures
appearing on TEPCO’s website).
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Fig. 2
East-west elevation plan of Fukushima Daiichi NPP Unit 1 reactor
building (prepared by the Citizens’ Nuclear Information Center, based
on figures in documents for application for permission to make changes
in the arrangement of the nuclear reactor)
|
The Missing Heavy Steel
Cover of the Equipment Hatch Provides Evidence that the Hydrogen
Explosion at Unit 1 Occurred on the 4th Floor
Late last year I became aware that further proof of
a small-break LOCA in the IC pipes had been found. During the NAIIC
investigation, and after it was dissolved, I happened to see on my
computer numerous times the motion videos taken by cameras surveying
the interior of the 4th floor of the reactor building (videos that had
all been shot by TEPCO and released on TEPCO’s website), and that
provide the evidence.
(6)
TEPCO investigated the 4th floor of the Unit 1
building several times, and each time they recorded scenes of violent
destruction of the 4th floor interior in their survey videos (Photos 1
and 2). TEPCO gave the following explanation on what could have caused
such violent destruction in its final report published in May of last
year.
(7)
On the fourth floor of the R/B where the IC main
unit is installed, there was a hole on the north ceiling due to the
hydrogen explosion on the fifth floor, and removed insulation and
debris were scattered on the north side of the top portion of the IC
thought to be caused by the explosion’s blast. The insulation on the
south side of the IC was severely torn and removed on the R/B equipment
hatch side (opening). It is considered that the hydrogen explosion on
the fifth floor blasted through the opening and damaged the insulation
on the IC. No insulation on the third or second floor was removed or
scattered.(author’s italics)
In other words, TEPCO’s conclusion is that all of
the violent destruction of the 4th floor interior was caused by the
blast from the hydrogen explosion on the 5th floor.
For example, the explanation in the excerpt above
says, “
The insulation on the south side of the IC was severely torn
...” Indeed, Photo 1 shows the metal cover and insulation on the IC
units (cylindrical tanks) had been violently stripped off. TEPCO adds
the explanation that this occurred because of the blast from the
hydrogen explosion on the 5th floor passing through the opening
(equipment hatch). Such a case, however, would have been
impossible, as explained below.
The opening described in the explanation is a
square-shaped hatch with sides of about 5 meters each on the floor of the 5th
storey (i.e., the 4th storey ceiling). This hatch is used when
delivering large pieces of equipment or materials, so it is often
simply called an “equipment hatch,” but when it is not in use, it is
covered with a steel lid (weighing about 1.5 tons), as shown in Photo
3, to prevent falls. Also, during the NAIIC investigation, we confirmed
that the equipment hatch had been in use shortly prior to the
earthquake, but had been closed, according to veteran workers, after
the delivery operations had finished, just a little before the
earthquake.
In other words, at about 2:30 p.m. on March 11,
2011, the equipment hatch was closed. From then on until after 3:30
p.m. on March 12, when the hydrogen explosion occurred, the hatch
should have remained shut, so inasmuch as the steel hatch was not
blasted downward into the 4th floor from an explosion on the 5th floor,
there should not have been any blast coming through the equipment hatch
and tearing insulation off the IC units on the 4th floor, and judging
from the lack of any hatch being discovered on the 4th floor, it can be
said that nothing of the sort happened.
On the other hand, as Photo 4 shows, it is an
uncontestable fact that the steel lid of the equipment hatch has
completely vanished. So, where did the hatch go and how did it vanish?
This mystery is solved easily if we say the
explosion occurred on the 4th floor and not on the 5th, as TEPCO and
many specialists are saying. If the hydrogen explosion occurred on the
4th floor, it would have raised the lid from below and the violent
blast would have blown it away, consequently falling somewhere on the
5th floor or may even have been sent flying outside from the 5th floor.
|
|
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Photo 1: The two IC units (4th fl., Unit 1 bldg.)
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Photo 2: Immense destruction on the 4th floor of the Unit 1 building.
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Photo 3: The steel lid of the equipment hatch on the 5th floor of the Unit 1 building.
|
|
Photo 4:
Looking up from the 4th floor to the equipment hatch (the steel lid
blown away by the hydrogen explosion is missing, an IC unit is visible
to the right).
|
Was the Source of the Hydrogen on the 4th Floor from the IC Pipes?
But why then did a hydrogen explosion occur on the
4th floor? What would the supply route of hydrogen to the 4th floor
have been?
It doesn’t take long to find an answer to this. The
hydrogen would have originated from a reaction between water and
zirconium in the damaged nuclear fuel rods inside the reactor pressure
vessel. The hydrogen thus generated would have entered the IC steam
pipes and led by them ultimately to the 4th floor of the nuclear
reactor building. Therefore, if the IC steam pipes or the drain pipes
beyond them (steam condenser pipes) had been damaged by the seismic
motion, the hydrogen would have been leaking from them continuously
inside the 4th floor.
The water-zirconium reaction occurs at above 900°C,
so the hydrogen reaching the 4th floor of the reactor building would
probably have been at about that temperature. The 4th floor, where the
two IC units were located could be said to be a sealed space, so if
hydrogen at more than 900°C was gradually building up in that space, in
the course of time it would have resulted in a large-scale hydrogen
explosion through spontaneous combustion.
Regarding a 5th Floor Hydrogen Explosion
I must add that I am not asserting that no hydrogen
explosion at all occurred on the reactor building 5th floor. It would
be natural to think that perhaps a hydrogen explosion also occurred on
the 5th floor. The reason is because the hydrogen generated in the
reactor pressure vessel, as many experts have pointed out, is thought
to have leaked into the 5th floor from the flange joint on the top lid
of the containment vessel. Then, by the time the hydrogen explosion
occurred on the 4th floor it is thought that quite a large volume of
hydrogen would have accumulated on the 5th floor as well.
The walls of the 5th floor of the Unit 1 building,
however, were not made of thick steel-reinforced concrete like the
other floors, but with simple panels stuck onto a steel frame
structure, so the 5th floor would have been affected by the cold
atmospheric temperatures outside along the coast in March, and it is
inferred that the temperature inside was not very high. If that is the
case, there would have been no spontaneous combustion of the
sequestered hydrogen. If a hydrogen explosion occurred on the 4th
floor, however, due to spontaneous combustion, it would have blown the
hatch off from the large object delivery port on the 5th floor, and it
is thought that the hot blast violently entering the 5th floor would
have instantaneously caused a hydrogen explosion on the 5th floor.
[Notes]
(1)
Ito, Y. (2013) Total loss of AC power at the Fukushima NPP Unit 1 was
not caused by the tsunami, Science Journal Kagaku, September 2013,
pp.1045-1054.
(2)
Tanaka, M. (2013) What does the violent destruction on the 4th floor of
the Fukushima Daiichi NPP Unit 1 reactor building signify? –Questioning
anew the possibility of an IC pipe rupture due to seismic motion,
Science Journal Kagaku, September 2013, pp.1055-1066.
(3) CNIC-Ustream of Mr. Ito on the SBO: http://www.cnic.jp/movies/5385
(4) CNIC-Ustream related to this article: http://www.cnic.jp/movies/5373
(5)
The Diet’s Report on the Investigation into the Accident can be read or
downloaded at:
http://warp.da.ndl.go.jp/info:ndljp/pid/3856371/naiic.go.jp/index.html
(6) http://photo.tepco.co.jp/date/201110-j/111021-02j.html
(7) http://ww.tepco.co.jp/nu/fukushima-np/interim/inex-j.html
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