This is one section of our annual report, the full report can be found here.
We will be posting a section per day over the next week for ease of reading.
Typhoon Hagibis caused minor landslides at Fukushima Daiichi. Other damage and water infiltration was minimal and did not cause any reported emergencies on site. (39)
Water infiltration from the typhoon was primarily water retention in building basements or at water treatment sites equipped with flood alarm systems. (40)
Construction of a tsunami wall has been delayed again and is now scheduled for construction in 2021. 50 locations at the plant lack sufficient protection from tsunami damage. (41)
A fuel removal robot will have a test run at Daiichi. The hydraulic robotic arm technology is scheduled for eventual fuel debris removal work. A sump pump in the basement of unit 3 sits in an area of highly radioactive water. To replace this pump so water can be removed, the muscle robotic arm will be used. This spares workers high levels of radiation exposure and provides a test run for this technology in a lower consequence environment.(42)
The frozen wall appears to be having more problems. Sections of the wall have partially thawed, even where the wall is operational. Surface
thawing is also seen on the sea side sections. TEPCO provided no explanation for the new changes. This has taken place over the winter. How this changes as weather warms will be of interest. (43)
Hydraulic robotic arm at a research facility in Japan (photo below)
Diagrams of the frozen wall sections, thermal reference on the right of each image.
(Above right) Blue shows operational sections, red shows sections with brine circulation turned off (images TEPCO)
The ongoing proposal to dump contaminated water into the sea has caused much international concern. Announcements that this is happening are untrue, the local approvals needed to do so have not been given. There is significant local opposition including from the fishing industry. (44)
Efforts to reduce the leakage of contaminated water on site continues. A below ground connection between units 1 and 2 has been plugged to prevent contaminated water from flowing between the two
buildings. (3) The ongoing transfer of contaminated water from building basements has an expected completion date of some point in 2020. Completion of this work have been hindered by findings of highly contaminated water in some areas. Water levels in the turbine buildings have been reduced to the lower basement level.(3) This reduction did not include reactor building basements or the torus room areas.(2)
(below) Sludge found in unit 2’s torus room show concentrations of radioactive substances (Photo TEPCO)
Processed contaminated water on site has been fully transferred to welded tanks (no longer in bolt together tanks).(3) The bolt together tanks have been a long term concern as they were only rated for 3-5 years of use. TEPCO has been inspecting welded water tanks with a ROV robot after some of the tanks were found to be producing hydrogen sulfide gas. The tank described in a recent report holds water after treatment by the ALPS water treatment system. ALPS is typically the last step of filtration. A large pile of sediment was found in the tank they inspected. TEPCO provides no explanation for what they found.
This raises questions about the effectiveness of the ALPS system, what is in the sludge, and if this water is really “safe” enough to dump in the ocean. (45)
(Below) images of found tank sludge (TEPCO)
The production of contaminated water on site has been reduced down to 150 m3 /day as of 2020. It had been over 400 m3/day in 2011. Work to install various water diversion and retention systems has contributed to reducing the daily contaminated water volume.(2) The injection of cooling water into the reactors has been reduced over time. This has helped to reduce the amount of generated contaminated water. Cooling water was changed to a “loop” system years ago. This takes contaminated water from the building basements, purifies it then injects it back into the reactors for cooling. These various tactics have greatly reduced the daily water volume.
TEPCO considered an unusual solution to their contaminated water problem. In September they published a handout about a floating shore tank. These are large barge type vessels used to hold oil. TEPCO confirmed the giant barge would be
impossible to use at Fukushima Daiichi. It requires five times the water depth than the depth of the port. The ship is too large to fit into the port and would be a safety risk in the event of a tsunami that could push it on shore. This report raises the question, why were they considering this in the first place? (46)
Removal of the highly radioactive unit 1-2 vent tower began this year. Structural damage to the vent tower from the earthquake and the unit 1 reactor explosion caused this work to be prioritized ahead of work rated as a higher risk, such as removing spent fuel. The tower is both a structural hazard and a contamination hazard.
Top and middle portions of the tower are being removed, the base levels of the tower will remain for now. This base section includes portions that are highly contaminated. (3)
The work to cut down the vent tower has not been without problems. A mishap in the calculation of the tower height caused a long work stoppage. An increase in soil height in the area where the crane was placed solved the problem. This gave the crane sufficient height clearance to overcome the miscalculation. (47)
The tower cutting rig experienced multiple failures. Cutting saws, stabilizers and the wifi communication system all experienced failures. Changes to the work procedures and equipment allowed work to resume. (48)
Vent tower progress has been slow but steady. High winds have caused some of the delays. The top sections were successfully removed and work on the mid-section is under way. (49)
Work was paused during February for routine inspections of the crane and will continue after completion of inspections.(50)
Workers have been monitoring a water sump at the base of the vent tower. This area is highly radioactive and is the route rainwater drains out of the vent stack. In December they discovered water was leaving the sump and they had no idea where it went. (51)
A converted bus has been used as the remote command center for the vent tower work. This bus is connected by a group of cables to a portable power generator. The key had been left in the bus ignition switch. For an unexplained reason, a worker turned on the bus engine.
A malfunction in the electrical system caused the bus to begin moving while none of the braking systems would respond. They were eventually able to stop the bus, but not before breaking the cable to the generator. TEPCO has now stored the bus key in an office to prevent another run away bus adventure. (52)
Spent fuel stored on site has gradually shifted location. The common pool is nearly full at 90%. Cask storage up on the hill is at about 69% full. Unit 4’s spent fuel pool is emptied and unit 3’s spent fuel pool has 503 assemblies of spent fuel left to be removed. (3)
The unit 1-2 and 3-4 vent towers were included in the ongoing inspections at Daiichi by Japan’s nuclear regulator (NRA). NRA has considered the shared vent towers as a significant indicator of what events took place during the meltdowns. (52)
Inspections included the area around each vent tower and the SGTS (Standby Gas Treatment System) filter rooms. This system provides radioactive material air filtration during normal operation. The inspections of SGTS systems in reactor buildings excluded unit 1. The SGTS room door in unit 1 had over 5 Sieverts/hr of radiation when this area was checked in 2012.
The NRA inspections included taking radiation readings where possible and the use of a gamma camera to identify hot spots of radiation at a distance. This work found more detail about the tower contamination than TEPCO’s previous investigations have reported.
Unit 1-2 Vent Tower & Piping Radiation
The unusual radiation found in the small pipe bend coming from unit 2 in the red circle is identified by NRA as the FSTG pipe. We were able to identify this as some form of radioactive vent pipe that routes from the unit 2 waste handling building that is attached to the reactor building. Why this section of pipe became contaminated wasn’t immediately clear, it may have been due to backflow from the venting of unit 1.
These images by NRA add some clarity to the issue. The FGTS line runs under the SGTS line and then connects directly into the large main venting pipe. This downward connection, if it lacked any sort of backflow limiter may have allowed condensation
and pressurized steam to collect in this small pipe during the venting operations. It connects into the common section of the large emergency venting pipe, so it has a direct connection to the route of unit 1’s venting.
Unit 2 Ventilation System Inspection
(Picture 1) Diagram of vent piping system for unit 2
(Picture 2) Radiation hot spots in SGTS HEPA filter system Unit 2
(Picture 3) Vent system rupture disc from below
(Picture 4) Vent system rupture disc readings at the disc location
NRA cites that various factors during the venting will impact how the tower is contaminated. The amount of steam, pressure within the pipe and water vapor condensation all play a role. The images of unit 2’s SGTS system and the rupture disc show that the system may have prevented venting of the reactor via the tower. TEPCO has refused to provide video evidence of their inspection of this area, leaving concerns that they had fabricated evidence. NRA’s inspections appear to confirm this rupture disc indeed did not work. This puts more of the potential releases from unit 2 out the reactor well and blow out panel. Those areas are known to have failed and generated large volumes of steam.
NRA Unit 3 SGTS Inspection
The unit 3 SGTS system resides in an accessory building between the reactor building and the turbine building. This spared the system the kind of damage the reactor building experienced. NRA posted a diagram of the radiation levels in the SGTS filter bank without any photos. It is assumed the inspection was done in person rather than with a robot. TEPCO to date has not provided any information on this system.
Radiation levels before and after the rupture disc are significantly higher than the background radiation. This appears to indicate some level of successful venting via this line. Visual evidence from the plant during the meltdowns showed at least some release out the vent stack.
Diagram below of unit 3 rupture disc (photo NRA)
Emergency venting is not done through the filter banks. The emergency venting system bypasses the filter banks but there are some interconnected portions. This makes the filter banks and their contamination levels of interest. The B filter bank shows what appears to be contaminated back flow from the emergency vent system backward into the filter bank. The A filter bank shows what appears to be contamination from the reactor building side. This could have come from contamination in the building air handling system.
NRA Unit 3 – 4 Vent System Inspection
This inspection work attempted to determine how hydrogen from unit 3 flowed into unit 4. NRA estimates that 25% to 29% of the hydrogen from unit 3’s containment at the time of venting, flowed to unit 4. The back flow of hydrogen into unit 4 is considered to have multiple causes. One being the lack of a backflow limiter at the SGTS filter bank. All of the dampers on the SGTS system at unit 4 failed open when AC power was lost. NRA also mentions that the vent line was modified after initial construction to “using the majority of the SGTS system”. While their translation isn’t specific, it appears the emergency venting system, the building ventilation system and SGTS filter system were intertwined in an unusual manner. (53)
NRA estimated the amount of hydrogen generated based on known and projected data points from the reactor failure at unit 3. This was input into a computer model of the piping systems to estimate the hydrogen flow into unit 4. Unit 3 has a “check valve” on the outgoing end of the SGTS filter system.
This prevented backflow into the building. The mention by NRA may be critical to understanding the meltdown and explosion at unit 3. TEPCO has insisted that venting efforts at units 1 and 3 caused hydrogen to backflow from the emergency venting system into the building air handling ductwork via the SGTS filters and system. NRA confirms there are check valves preventing that. The radiation readings found in the SGTS filters appear to show there wasn’t a significant backflow into the building.
Hydrogen in the ductwork in the building may have been routed into the ducts by other means. NRA’s refined estimate is that 35% of the vented hydrogen from unit 3, reached unit 4. They estimate 300 – 500 kg of hydrogen flowed into unit 4. This number could be influenced by various factors in their estimates. By their estimates, the backflow into unit 4 could be enough to cause the explosion at unit 4. (54)
NRA plans further inspections including:
Unit 3’s containment cap and reactor well inspection, conducted from the refueling floor area. They plan to look for fuel particles, evidence of heat damage and at the connection between the containment cap and the spent fuel pool. Inspections will attempt to identify the distribution of contamination and fuel particles on the underside of the concrete reactor well cover. This may help confirm behaviors during the explosion at unit 3, and how much radioactive material was ejected from specific locations. Work to identify leaks from containment including using a gamma camera are planned. This could involve numerous locations within the reactor building.
For unit 1 NRA plans to obtain the existing reactor well inspection data from TEPCO for further analysis. This review may help determine how much hydrogen would be required to cause the damage found in the reactor well. This piece of information could significantly improve understanding of the failure at unit 1.
NRA will look for damage and leak points related to the hydrogen explosion at unit 1.
NRA plans to obtain operational records and design drawings for the plant. They plan to obtain these from the administration building at Daiichi. TEPCO claimed all such documents were destroyed during the tsunami. The building itself while damaged and flooded inside, retained most of the office equipment inside the building. If the documents are in any sort of usable condition 9 years later remains to be seen. (55)
TEPCO has added a new waste storage building (building 9) to on site storage. Construction was started in 2018 to hold new debris generated from units 1 and 2 demolition activities.(3) About 460,000 m3 of solid waste was stored on site as of March 2019. This includes building rubble, felled trees and used protective gear. All of this is stored in temporary storage facilities on site. Roughly 4300 used water filtration canisters are currently stored on site in shielded storage.(3)
A “hot lab” under construction near Fukushima Daiichi for highly radioactive material analysis nears completion. Laboratory-1 of the Radioactive Material Analysis and Research Facility is expected to open at the end of FY 2020.
The new lab in Okuma will allow researchers to investigate fuel debris samples and other highly radioactive materials from Fukushima Daiichi.(3)
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