Current State of Post-Accident Operations at Fukushima Daiichi Nuclear Power Station (July to December 2013)
State of the Plant
As a result of the accident, many of the measuring
instruments installed in the Fukushima Daiichi Nuclear Power Station
(FDNPS) measuring system are malfunctioning. There is doubt about the
accuracy of values being measured, but if these values are taken as the
premise, from the temperature of the containment vessel and from the
release of Xenon-135, a noble gas that is released when nuclear fission
takes place, it can be estimated that the state of the reactor is
stable.
However, even now 10 million Bq/hr of radioactive
substances are being continually released into the atmosphere (see
Figure 1). (The leakage of contaminated water will be mentioned below.)
Additionally, the Tokyo Electric Power Company
(TEPCO) board of directors’ meeting on December 18, 2013 decided to
decommission of Units 5 and 6, and the notification to decommission the
reactors was delivered to the Minister of Economy, Trade and Industry
on January 31, 2014.
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Figure 1; Releases of radioactivity from Units 1 to 4 of Fukushima Daiichi Nuclear Power Station
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Current State of Post-Accident Operations
1. State of Operations concerning Molten Fuel
The current state is that for each of the reactors a
survey of the situation inside the reactor; surveys, research and
remote-control removal of debris with a view to decontamination of the
buildings; surveys to reveal the locations of leaks from the
containment vessels, and other work is being implemented.
2. State of Operations concerning Spent Fuel Pools
The spent fuel pools at FDNPS were badly damaged by
the earthquake and accident. In the case that aftershocks cause further
damage to the buildings and coolant water leaks occur from the spent
fuel pools (SFPs), in which a large number of fuel assemblies is stored
(Table 1), there is the possibility that fuel assemblies could melt
down. Because of this, it is necessary that the fuel assemblies be
removed from the SFPs and transferred to the safe common pool at the
earliest possible stage.
Operations to remove fuel assemblies from the SFPs
have started with Unit 4. Large pieces of fallen debris in the upper
part of the building and in the SFP itself have been cleared away, and
removal of the fuel assemblies began in November 2013, following the
construction of a cover and crane for the fuel removal
operation.Elimination of debris from the upper part of the Unit 3
building is almost complete and the plan is now to implement dose
reduction measures on the 5th floor of the building, the operating
floor, where the dose is currently too high to allow access by human
workers, and then remove large pieces of debris from inside the SFP.
In order to carry out debris removal from the upper
part of Unit 1 around mid-2014, it is now planned to begin demolishing
the reactor building cover currently in place, and as a preliminary to
this the ventilator equipment collecting and filtering out the
radioactive substances inside the building cover has been stopped since
September.
Further, the dose inside Unit 2 is too high to allow
inspection of the detailed situation inside the building.
For the fuel assembly removal operation, 22 fuel
assemblies stored in the SFP are placed at one time in the previously
existing transfer vessel used for transferring the assemblies onsite.
This is then lowered a maximum of 32 m using the crane installed inside
the fuel removal cover and transferred to the common pool, which is
used for storing spent fuel in a separate building on the FDNPS
site.
There are however, many problems with this plan.
Especially grave is the fact that the repeated tendency of TEPCO to
play down safety aspects due to overoptimistic assumptions are also
apparent in these operations.
(1)
An example is that despite the fact that what we
have witnessed at FDNPS is a situation brought about by the
simultaneous destruction of multiple pieces of equipment caused by the
related actions of the earthquake and tsunami, TEPCO is still
maintaining the single-breakdown assumption to the securing of safety
in these removal operations. Moreover, we are unable to confirm an
emergency contingency plan for the case where an onsite transfer vessel
is dropped in the course of these operations. There are also concerns
over corrosion of the fuel associated with the injection of seawater
into the Unit 4 SFP at the time of the accident and over fuel damage
due to debris remaining in the SFP interfering with the removal of the
fuel assemblies.
There is also the problem of fuel damaged before the
accident, which is still stored in the SFP. There are three damaged
fuel assemblies stored in the Unit 4 SFP. These cannot be inserted into
the onsite transfer vessel. TEPCO is considering ways of handling this,
but one of the assemblies is seriously damaged, cracks having appeared
in the channel box (the long, square metal box fitted around the fuel
assembly).
In parallel with these operations, the fuel loaded
into the reactor cores of Units 5 and 6 is also being transferred to
the respective SFPs. The opening (removing the lid and so on of the
reactor vessel) of the Unit 6 reactor began in September 2013 and the
transfer of the fuel was completed on November 29.
Since the FDNPS common pool is almost completely
full, from June older fuel assemblies stored there have been transferred, in
order of age, to dry casks, and these have been moved to a temporary
storage facility that has been newly constructed on the site.
|
Reactor |
Spent
fuel pool |
Transferred fuel |
Full storage capacity (*1) |
Stored
fuel |
% |
Spent fuel |
New
fuel |
Spent
fuel |
New
fuel |
|
Damaged fuel |
Unit 1 |
400 |
900 |
392 |
44% |
292 |
70 |
100 |
0 |
0 |
Unit 2 |
548 |
1,240 |
615 |
50% |
587 |
3 |
28 |
0 |
0 |
Unit 3 |
548 |
1,220 |
566 |
46% |
514 |
4 |
52 |
0 |
0 |
Unit 4 (as of Dec. 22, 2013) |
0 |
1,590 |
1,401 |
88% |
1,221 |
3 |
180 |
110 |
24 |
Unit 5 |
548 |
1,590 |
994 |
63% |
946 |
1 |
48 |
0 |
0 |
Unit 6 (as of Nov. 29, 2013) |
(*2) 0 |
1,770 |
1,704 |
96% |
1,640 |
1 |
64 |
0 |
0 |
Common Pool |
- |
6,840 |
5,718 |
84% |
5,716 |
0 |
2 |
- |
348 |
Temporary dry
cask storage facility |
- |
(*3)
2,930 |
(*4)
1,067 |
26% |
1,067 |
0 |
0 |
- |
- |
|
Table1; State of the fuel assembly removal operation (as of Nov. 20, 2013)
(*1) However, there
is some spare capacity over and above the "full storage capacity" for
the number of assemblies to be loaded into the reactor core. This is
for the storage of reactor core fuel during regular maintenance. (*2)
Fuel assemblies in Unit 6 reactor transferred to spent fuel pool by
Nov. 29, 2013. (*3) Number of installed dry casks is 23 (dry cask
capacity is 50).(*4) 408 dry casks which became unusable due to the
tsunami on March 11, 2011 have been transferred here from the dry cask
storage building in FDNPS. Units: Number of fuel assenblies.
|
|
|
Transfer vessel
|
|
Spent fuel pool
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Loading the transfer vessel onto a trailer
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Photos by TEPCO
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3. Contaminated water problem
Measures planned against the continually increasing amounts of
contaminated water are as follows: Establishment and operation of the
“ground water bypass” to pump up ground water and release it into the
sea; water level management by restoration of the pumping wells, that
became unusable due to the accident, in the vicinity of the reactor
buildings (scheduled to resume operation in mid-FY2014); construction
of a water barrier on the land side of the reactors (scheduled to be
usable during the first half of FY2015); waterproofing of holes and so
on in the outer walls of the Unit 1 to 4 buildings (scheduled to be
completed in FY2017); work to decrease the volume of contaminated water
through operation of the multi-nuclide removal equipment (ALPS)
(scheduled for full operation around mid-FY2013); and increased storage
tank installations. However, as we have already reported in NIT156, the
gravity of the situation is continuing to increase, for example, with
contaminated water leakages from the water storage tanks and from the
turbine buildings.
Barriers have been established around the contaminated water
storage tanks, and valves have been installed to allow for the release
of rainwater and so on. However, at first these valves were left
permanently open out of concern that rainwater might overflow the
barriers. Since the contaminated water leakage incident that took place
in August 2013 the valves have been kept permanently closed, but the
necessity for countermeasures in the case that rainwater overflowed the
barriers was pointed out from the time when this operational change was
put into effect. It was decided that water inside the barriers would be
first transferred to a storage tank and then released only after the
level of contamination has been confirmed. However, the preparation of
hoses for the transfer of the water to tanks was not carried out
smoothly, and when heavy rain occurred on September 17, rainwater
overflowed the barriers, but TEPCO released the water after only a
simple measurement. At first, the results of these simple measurements were said to
be 2 Bq/l total beta radiation when the releases were begun, but it
later became clear that this was in fact a misreading of 24 Bq/l.
Looking at the accident list (Table 2), it seems that a large
number of other operational mistakes have also occurred. This gives us
a very strong impression not only of the severity of the post-accident
operations at FDNPS but also of the limits of TEPCO’s accident
management capabilities.
(Hajime Mastukubo, CNIC)
Date |
Location |
Content |
July-4 |
Unit 2 CST
reactor water injection system line |
When carrying
out the changeover work from the elevated reactor water injection system to
the CST (condensate storage tank) reactor injection system, the reactor
injection line valve in the turbine building, which should normally be in the
closed position, was in the open position and some of the water which should
have flowed to the reactor core spray system flowed into the feedwater
system. |
July-5 |
Unit
5 D/G (B) alert malfunction lamp |
The
Unit 5 emergency diesel generator B (D/G (B)) alert malfunction lamp (which
shows that the D/G is not in a state of alert) came on. It is thought that
this occurred due to the position of a fuel bundle shifting from its normal
position. |
July-5 |
Unit
5 D/G (B) air storage tank pressure |
It
was confirmed that the pressure in the air storage tank was reduced when the
Unit 5 D/G (B) was operated. It was thought that the solenoid valve pilot
sheet, a consumable item, had hardened, that air was escaping from the sheet
due to deformation, and that the solenoid valve was unable to close
completely. |
July-10 |
Unmanned
crane removing debris from the upper part of the Unit 3 reactor building |
Hydraulic
oil was confirmed to be oozing from the joint on the hydraulic hose on the
hydraulic cutter on the unmanned crane being used in debris-removal work on
the upper part of Unit 3 reactor building. |
July-18 |
Center
of Unit 3 reactor building 5th floor (equipment storage pool side) |
Something
appearing as steam was confirmed to be drifting around in the vicinity of the
center of Unit 3 reactor building 5th floor (equipment storage pool side).
(This later appeared continually in low temperature, high humidity
conditions.) There was no significant change seen in main plant-related
parameters, monitoring posts or continuous dust monitors, or in the
atmospheric dose above the reactor building spent fuel pool. |
July-23、24 |
Dust
radiation monitor in the ventilation equipment outlet in Unit 2 reactor
building |
An
alarm sounded indicating an abnormality in the equipment in the absorbtion
pump in the Unit 2 dust radiation monitor system B and the dust monitoring B
system was stopped. There was no significant change in the plant data, etc.
It is thought that the dust absorption pump stopped when the alarm sounded
indicating equipment abnormality due to a shift in the position detector on
the (motor driven) airtight device which locks in place the dust measurement
filter paper by pinching it. The equipment abnormality alarm also sounded on
July 24. |
July-25 |
Unit D/G6A |
As
a test of automatic startup of the Unit 6 D/G(A), when the Unit 6 6.9 kV
electricity distribution board C was shut down, the residual heat removal
system B, which was cooling the reactor, ceased operation. |
July-30 |
Second
cesium absorption device (SARRY) |
The
"booster pump stopped/leak detected" alarm sounded in the second
cesium absorption device (SARRY), which was currently in the process of
treatment operations, and shut down automatically. |
August-10 |
Underground
water storage tank Nos. 3 and 4 |
A
bulge of maximum height of approxiately 40 cm and to an extent of
approximately 30 m × 20 m
occurred around the center of the embankment of the No.3 underground water
storage tank. A buldge also occurred around the center of the upper surface
of No.4 underground water storage tank, with an extent of approximately 10 m
× 10 m. It is thought that the cause is the tendency for the ground water to
rise in the vicinity of the underground water storage tanks since mid-July. |
August-12、19 |
Important
anti-seismic building |
An
alarm sounded to indicate a high level of radiation in a continuous dust
monitor at the front of an important anti-seismic building on August 12. It
was confirmed that 10 out of 16 people who had boarded an onsite bus from the
important anti-seismic building had bodily radioactive contamination. Two out
of three people who boarded an onsite bus at the important anti-seismic
building on August 19 were also confirmed to have bodily contamination. It is
thought that this problem was due to dust drifting on the wind when debris
was amassed and removed after removal of a ceiling crane girder during the
debris removal operations in the upper part of Unit 3 reactor building. |
August-19 |
H4
area tank |
It
was confirmed that the water level in the H4 area No.5 (H4-I-5) tank had
fallen by about 3 m (roughly 300 m3). It was confirmed that the wall of the drainage channel to
the east side of the H4 area tank had evidence of streak-like flow marks
(surface dose equivalent rate 6.0 mSv/h (gamma + beta radiation (70 μm dose
equivalent rate)) and thus there was a possibility that contaminated sludge,
etc. had flowed into the drainage channel. Tanks in several areas were later
confirmed to have places with high radiation doses. |
August-24 |
Gas
management system of the Unit 2 reactor containment vessel |
A
fall in pressure in the Unit 2 reactor containment vessel and reduction in
ventilation flow of the gas management system of the reactor containment
vessel occurred. The amount of radioactivity of the gas released was assessed
as around 2 × 104
Bq. |
September-5 |
Large
crane for debris removal on the upper part of Unit 3 reactor building |
The
jib (crane arm) of the 600 ton crawler crane being used in the debris removal
operations on the upper part of the Unit 3 reactor building collapsed
sideways and it was confirmed that the part where the jib joins the main mast
was damaged. |
September-12 |
Units
5 and 6 RO (reverse osmosis membrane) device |
Water
was discovered leaking from the Unit 5 and 6 retained water treatment device.
The estimated amount of the leakage was around 65 l of water treated by the
RO device.The radiation concentration of the leaked water was below the
detection limit for Cs-134, 4.2×10-3 Bq/cm3 for Cs-137, and below the detection limit for total beta. |
September-15 |
B
South tank area dike |
Water
accumulated behind the B area tank dike overflowed and the water that had
accumulated behind the dike was transferred to a B area tank. The water that
had overflowed had a total beta value of 37 Bq/l. The level of water behind
the tank dike rose due to rain associated with an approaching typhoon on
September 16. The water well below the notification criterion for Sr-90 of 30
Bq/l was released outside the tank dike (7 areas, total volume approximately
1,130 m3). Water
other than this was pumped into a tank within the area (12 areas, total
volume approximately 1,410 m3). |
September-18 |
Central
section of Units 1 and 2 exhaust stack |
During
a seismic safety assessment of the Units 1 and 2 exhaust stack, it was
confirmed that the steel material in the exhaust stacks (bents) showed
damaged locations such as with subsidiary fracture, seeming subsidiary
fracture or rusting. Since there are places with high dose rates in the area
of these exhaust stacks, it is planned to begin an investigation after
detailed investigation method, etc. has been considered. |
October-1 |
H6
area notch tank |
When
transferring rainwater behind the H6 area dike to the H2 south area dike,
part way along the hose used to transfer the water the water overflowed from
a notch tank. The volume of water leaked was about 5m3 and radiation in the water in the notch tank was Cs-134: 8.0
Bq/l, Cs-137: 16 Bq/l, Total beta: 390 Bq/l (Sampled on October 1). |
October-2 |
H8 south tank
area |
Due to the
impact of a typhoon, the water level behind the H8 south tank area dike rose
and overflowed the dike. The result of radiation measurement of the water
accumulated behind the dike showed Cesium-134 and 137 to be below the
detection level and total beta to be 15 Bq/l. |
October-2 |
G3 east tank
area |
It was
confirmed that rainwater had reached the upper part of the dike in the G3
east tank area (welded tanks). Water that had accumulated behind the dike was
transferred to a tank in the same area. Radiation measurement results showed
that the water that had accumulated behind the dike had Cesium-134, 137 and
total beta of below the detection limit. |
October-2 |
B south area
tank |
To prevent the
overflow of rainwater from the typhoon, when rainwater behind the B south
area dike was transferred to tanks in the same area and in other areas,
around 17m3 of
water leaked into the area behind the dike from between the roof panel and
the side panel of the tank because it had been constructed on sloping land,
and approximately 430 l of water leaked outside the dike. The leaked water
was water that had already undergone the water conversion treatment process
(total beta: 580,000 Bq/l, Cesium-134: 24 Bq/l, Cesium-137: 45 Bq/l (sampled
on October 2)). It is possible that the water flowed into the sea through the
gutters and drainage channels. |
October-3 |
Unit 5 floor
drain collector pump gland water outlet pipe |
Water leaked
from the floor drain collector pump water outlet pipe in the Unit 5 waste
treatment building. The volume of the water was approximately 500 ml. |
October-9 |
Water
conversion device RO-3 temporary house |
A
leak occurred in the temporary house while during work to change to PE pipes
was being carried out when the cam-lock (joint) for a pressure hose in a
location other than that to be changed during the work was mistakenly
removed. The volume of water leaked was approximately 7m3. |
November-15 |
G6
south area tank |
Leakage
was confirmed from the lower two tank side wall joints (flanges) of the steel
tube type tank G6-C3 in G6 south area. The result of the radiation
measurements was that the water dripping down and accumulating in the
horizontal flat part of the flanges showed 35 mSv/h (gamma + beta (70 μm dose
equivalent rate)), 0.03 mSv/h (gamma) (at a distance of 5 cm). |
November-19 |
Emergency
nitrogen gas separation device |
The
air-operated valve on the emergency nitrogen gas separation device supply
line failed to operate. |
November-23 |
Nitrogen
gas separation device (A) |
While
running the two (A and B) Nitrogen gas separation devices, which pump
nitrogen into the Units 1 to 3 reactor pressure vessels and reactor
containments, the “dryer abnormal current or dryer high pressure cut” alarm
sounded and the nitrogen gas separation device (A) ceased operation. |
November-26、
December-9 |
GIS
interface board |
The
“South 66 kV onsite transformer 2B abnormal GIS” alarm sounded and at the
same time the same alarm automatically reset itself. Evidence that a small
animal had entered this GIS interface board (a relay board which collates
information from the control boards at the site and sends it to the switching
station system) was discovered. On December 9, the alarm “South side 66 kV
Okuma line 3 L light malfunction” also sounded (this alarm automatically
reset). It was confirmed that a small animal had entered the interface board. |
December-11 |
Unit
3 spent fuel pool alternative cooling system secondary system (system A) |
It
was confirmed that filtered water at the rate of about one drip per five
seconds was dripping from the metal flexible hose joint in the Unit 3 spent
fuel pool alternative cooling system secondary system (system A). The extent
of the leakage was approximately 50 cm × 40 cm. |
December-18 |
F
area C5-C6 tank connecting pipe |
It
was discovered that water was leaking at a rate of approximately one drop
each minute from the joint (on the C5 tank side) of the C5 and C6 tank
connecting pipe in the F area tanks (north of Units 5 and 6). The extent of
the dripping was approximately 30 cm × 5 cm × 1 mm (thickness). |
December-22 |
H5,
G6 tank area |
Water
was confirmed to be leaking from the lower part of the dike on the west side
and the seam of the dike on the northeast side of the H5 tank area. Leaks
were also confirmed from the lower part of the dikes on the north and west
sides of the G6 north tank area. Leaked volumes of water (volume of water
that seeped into the soil) were estimated to be approximately 1.0 m3 in the northeast side
of the H5 tank area and approximately 0.8 m3 in the G6 north tank area. |
December-24 |
H4
tank area and H4 east tank area |
The
water level behind the dikes in the H4 tank area and H4 east tank area fell.
Leaks occurred. The leaked volume from the H4 tank area was estimated at
approximately 116 m3
(Strontium-90: 20 Bq/l, Cesium-134: below detection limit, Cesium-137: below
detection limit), and from the H4 east tank area the leaked volume was
estimated at approximately 109 m3 (Strontium-90: 440 Bq/l, Cesium-134: below detection limit,
Cesium-137: below detection limit). |
|
Table
2; List of Accidents, July to December 2013 (Excerpted from TEPCO
website and Nucia, the nuclear facility information disclosure library)
|
[Note]
(1) A statement issued by CNIC concerning the removal of fuel
assemblies from Unit 4 can be seen at http://www.cnic.jp/5475 (in
Japanese)
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