With the 3rd anniversary of the 3-11 triple disaster approaching we have taken a look at the changes that have taken place at Fukushima Daiichi. Unit 1:
In July TEPCO admitted that both the reactor and containment caps are leaking. TEPCO mentions it leaks nitrogen but that would permit anything else to leak out through the same path. They also admitted the downcomer expansion bellows were leaking nitrogen and steam in the torus. The upper leaks could have been the motivation for the rush to put a tent cover over unit 1 back in 2011.
This was also the point where TEPCO admitted the torus structure of units 1-3 were leaking in some manner. They did not futher clarify how they assume them to leak.
TEPCO sent in a pair of robots to inspect the unit 1 personnel access hatch room. They found blistered paint, discoloration on the access hatch and a leak around the HPCI system. It was not clear what TEPCO was looking for in here, they did give the HPCI pipe a serious look. The discoloration and blistering could have been caused by excessive heat and appears more prominent closer to the containment wall. More photographs and details on this inspection can be found here.
TEPCO proposed the idea to fill the torus rooms with concrete in June in an effort to stem the ongoing leaks even though they were still trying to deny the problem. The plan to grout the torus room early in the decommissioning process raised some concerns since it is still considered likely there is melted fuel debris in the torus and torus room. This was also the point TEPCO began to consider the frozen wall plan that they had earlier rejected.
Workers at the plant expressed concern about the unanalyzed risks involved in the upcoming effort to remove spent fuel from unit 1. Some of the concerns were that the foundation of the reactor building can’t be inspected due to the high radiation levels. This means that any additional weight on the building could cause a structural problem. TEPCO’s later roadmap documents showed they may put a new building to remove fuel similar to unit 4 where it does not rely on the structural integrity of the reactor building. The cask weight in the pool would still be a risk that needs to be explored. The structural analysis or details of the unit 4 defueling building have not been made public. That building has been in operation for a few months so far.
By August the first hints of the highly contaminated groundwater leaking to the sea came out. Highly radioactive water in a tunnel near unit 1 was blamed on rainwater, over time TEPCO dropped this excuse. The levels were considerably higher than anything found in 2011. These levels seem small by comparison to what is found in the groundwater later in the year.
TEPCO admitted a direct groundwater leak into the unit 1 turbine building. They have known about it since May of 2011 and at some point dumped concrete around it to try to slow the leak. Video showed it was still allowing a considerable flow of groundwater through the opening.
By November TEPCO had admitted that unit 1 has 70 damaged fuel assemblies from before the disaster in the spent fuel pool. This is 17.8% of the total fuel in the pool. Some have been there as long as 40 years. Instead of trying to remove these as they became known TEPCO has opted to let them build up in the spent fuel pool. This will create additional challenges when they attempt to begin removing the spent fuel.
IRID, the new decommissioning authority in Japan made an interesting admission on unit 1 that the fuel had come within one foot of burning through the containment concrete basemat.
“Computer simulations show the melted fuel in Unit 1, whose core damage was the most extensive, has breached the bottom of the primary containment vessel and even partially eaten into its concrete foundation, coming within about 30 centimeters (one foot) of leaking into the ground.”
The statement was almost shocking after over two years of denials by TEPCO that unit 1 had significant failures. IRID’s statement appears to be well supported by research by the US national labs.
Hitachi used a new boat robot to investigate inside the unit 1 torus room. What TEPCO chose to release from this inspection was minus a substantial section of video in the area most suspected of possible containment melt through. Images from the portions of the video that were released can be found here.
Damage was found on the unit 1-2 vent tower. This caused considerable concern that the tower could come down in a strong earthquake. This vent tower had been the location of very high radiation in 2011. A new inspection found 25 sieverts/hour near the base. This lethal location creates a challenge for any effort to take down or stabilize the tower.
TEPCO sent in a robot team to investigate the high radiation levels found in unit 1 on the first floor. The emergency venting pipe from the torus was found to be the source of the high radiation (5 sieverts/hour).
Some of our other observations of this inspection:
- The highly radioactive pipe is the torus emergency vent pipe (this leads out to the vent tower)
- It is possible the pipe itself has shifted position laterally up to 2 inches based on 2011 and 2012 images, there is concern the pipe may have broken below the floor
- The elbow in the pipe is considerably more radioactive than other portions of the pipe
- TEPCO thinks the high radiation is higher below the floor. The area around the pipe penetration is about 5 Sv/h, too high for workers to approach
- Areas of the pipe that run across the 1st floor area are over 1 Sv/h
- The pipe of a standby cooling system also had elevated radiation levels
TEPCO still plans to remove the cover on unit 1 in 2014. They insist it won’t raise radiation levels in the area or releases from the plant significantly, many are skeptical. Many details about what has taken place inside unit 1 and what this means for the environment and decommissioning remain to be seen.
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