Tokyo Electric Power Co. shows its installation work to cover the upper part of the No. 3 nuclear reactor building that was blown off by the March 2011 hydrogen explosion at the Fukushima No. 1 nuclear power plant.
OKUMA, Fukushima Prefecture–Tokyo Electric Power Co. showed reporters its progress in installing a new roof above Fukushima No. 1 nuclear plant’s No. 3 reactor building on Aug. 2, ahead of work to remove spent nuclear fuel from a storage pool.
The company demonstrated how it is carrying out the work, which is necessary because the upper section of the reactor building was blown off in a hydrogen explosion in the nuclear disaster at the plant in March 2011.
The roof project marks a step toward removing nuclear fuel assemblies in the spent nuclear fuel storage pool in the building.
A photograph taken from an Asahi Shimbun helicopter shows a section of the half-tubular shaped roof being installed over the No. 3 reactor building at the Fukushima No. 1 nuclear power plant on Aug. 2.
To prevent the spread of radioactive material, TEPCO started to set up the half-tubular shaped cover to shield the damaged reactor building at the end of last month.
A section of the roof is lifted by a crane to place it on top of the No. 3 nuclear reactor building at the Fukushima No. 1 nuclear power plant on Aug. 2.
An artist’s rendition of the completed roof that will shield the upper part of the No. 3 nuclear reactor building that was blown off in the March 2011 hydrogen explosion at the Fukushima No. 1 nuclear power plant.
The 566 nuclear fuel assemblies currently lying in the pool will become a significant risk if another major disaster strikes the area.
TEPCO is expected to start removing the fuel from around mid-fiscal 2018.
Early on Aug. 2, part of the roof measuring around 17 meters high and weighing 37 tons was lifted to the top floor of the reactor building with a large crane.
Workers connected the new part of the cover to another section that had been installed at the end of July, completing one eighth of the roof. When finished, it will be about 60 meters long.
Dedicated removal machines are needed to retrieve the fuel from the storage pool. The machines that had been used at the plant prior to the accident were removed because they were severely damaged by the hydrogen explosion.
Source : Tepco
2017.7.31 Installation of Unit 3 fuel removal cover dome roof at Fukushima Daiichi Nuclear Power Station
Installation of Unit 3 spent fuel removal cover dome roof at Fukushima Daiichi Nuclear Power Station (On-site demonstration) Photos taken on: Aug 2, 2017
TEPCO released three videos of its robot probe inspections inside unit 3. The videos provided some interesting information, showing some unexplained “blobs”, thick adhered substances, concrete spalling seen in fires, possible melted fuel formations, and thought to be solidified melted fuel around the lower end of a control rod.
TEPCO think the graphite gaskets sealing the control rod holes in bottom of the reactor vessel melted allowing molten fuel to flow through these holes to drip down into the reactor pedestal. Structures in the pedestal show some of the patterns created by the thick substances that appear to have splattered around the containment structures.
TEPCO cites 364 tons of fuel debris (melted fuel, internal reactor parts and control rods) to be expected at unit 3. The videos only show very small views of the damage found making it difficult to determine how much fuel debris was actually found inside unit 3’s pedestal.
Source : Tepco
This underwater robot was used in the recent probe of reactor 3 at the Fukushima No. 1 power plant.
The first images of melted fuel from the crippled Fukushima No. 1 power plant indicate that it did not burn through the pressure vessel of reactor 3, but exited through the holes used to insert the control rods, officials say.
While the landmark robot footage from the primary containment vessel of unit 3 is helping Tokyo Electric grasp the reality of the damaged fuel assemblies, it may also force it to rewrite the road map for decommissioning the meltdown-hit plant.
Tokyo Electric Power Company Holdings Inc., better known as Tepco, sent an underwater robot into reactor 3 earlier this month to confirm its hypothesis that the core — the fuel assemblies in the pressure vessel — broke apart and fell to the bottom, letting molten fuel burn through and drip into the primary containment vessel.
According to Tepco spokesman Takahiro Kimoto, however, the images taken beneath the PCV indicate the pressure vessel probably withstood the heat of the molten fuel. He said the fuel apparently seeped through the holes for the control rods.
“We do not presume that the vessel, which is 14 cm thick, melted and collapsed together with the fuel, but that part of the fuel instead made its way down through holes,” Kimoto said. The control rods are used to moderate the chain reaction and are inserted vertically into the core.
Tepco said it estimates reactor 3 has about 364 tons of fuel debris, and that similar amounts will be found in reactors 1 and 2. Removing the fuel from the reactors is the largest challenge in defueling the aged plant — a process that could take up to 40 years to complete.
The camera on the underwater robot also captured images of rubble around the fuel debris, which could slow the removal process. The rubble includes devices for supporting the control rods at the bottom of the PCV and scaffolding for maintenance workers beneath the pressure vessel.
Minister of Economy, Trade and Industry Hiroshige Seko said the government and Tepco will try to draft a plan for removing the melted fuel in September, with an eye to hammering out the specifics in the first half of fiscal 2018 and starting the work in 2021.
But the findings from reactor 3 may force them to alter the state’s road map for decommissioning Fukushima No. 1, officials said.
An entity providing technical support for the project has urged that efforts be made to remove the melted fuel from the submerged lower part of the PCV by keeping air in the upper part, according to a source familiar with the plan.
Although filling the PCV completely with water would largely reduce the radiation risk to the robot probes, the Nuclear Damage Compensation and Decommissioning Facilitation Corp. is reluctant to do so because it is damaged and the toxic water will just leak out, the source said.
At the other two reactors, Tepco thinks most of the fuel in reactor 1 fell to the bottom of the primary containment vessel, and that some of the fuel in reactor 2 remained in the pressure vessel. The company made the estimates based on cosmic ray imaging analysis and by sending robots and endoscopes into the PCVs of the two reactors.
On July 28 Tepco announced the unit 3 reactor muon scan preliminary results. The muon scan can detect masses of nuclear fuel if over at least a cubic meter.
Tepco declared that they will continue the muon scan, however this continued scan will certainly refine the data but not change much the results.
Tepco admitted finding no significant amount of fuel inside the unit 3 reactor vessel. These muon scans do not quantify possible fuel in the containment structure or in the base mat concrete of the building.
A recently done ROV inspection of the unit 3 containment structure, including the pedestal area below the reactor vessel, clearly located some melted fuel. However as the video and imagery published was limited and heavily edited, it is currently unclear how much fuel was found in that area.
Source : Tepco’s handout
Japan’s industry minister says the government hopes to have a policy in place by around September on how to remove melted fuel from the No.3 reactor of the disabled Fukushima Daiichi nuclear power plant.
Hiroshige Seko told reporters on Tuesday that a robotic probe has confirmed lumps that could be fuel debris in the No.3 reactor, giving researchers valuable information.
Seko said he hopes a policy on how to remove the debris can be formulated, based on an analysis and assessment of the probe’s findings.
During the survey last week, a submersible robot found lumps below the reactor pressure vessel and at the bottom of the containment vessel.
It’s the first time a probe has identified what could be a mixture of melted nuclear fuel and broken metal parts lodged inside a reactor container.
Removing the fuel debris would require the use of remote-controlled robots. It is considered the most challenging step in the process to decommission the reactor.
The industry minister suggested that the government plans to honor the existing timetable for decommissioning.
The plan calls for setting specific methods for removing fuel debris by the first half of 2018, so the actual work can begin by 2021.
The operator of the damaged Fukushima Daiichi nuclear power plant released video footage on Monday of what is likely to be melted fuel debris.
Tokyo Electric Power Company, or TEPCO, found the solidified lumps during a robot inspection of the containment vessel of Fukushima’s wrecked No. 3 reactor. The 3-day survey ended on Saturday.
TEPCO had earlier only made public still images from the probe. The 4-minute video shows black or grey lumps hanging down close to a structure just below the reactor.
The lava-like lumps are piled in layers, a phenomenon unknown before the accident.
TEPCO officials say the debris is probably melted nuclear fuel mixed with broken reactor parts.
In addition to metal scaffolding and other structural components, rocks and sand-like sediment can be seen getting stirred up by the movement of the robot.
The government and TEPCO plan further analysis of the footage in order to determine methods for removing the debris.