TEPCO Opens Up Space in Common Pool at Fukushima Daiichi to Receive Spent Fuel from Unit 3

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“X-6 penetration” at Unit 5
4 June, 2018
On May 31, the Tokyo Electric Power Co. (TEPCO) released a progress report on the decommissioning at the Fukushima Daiichi Nuclear Power Plants.
Four days earlier, on May 27, the power company began transferring some of the spent fuel currently stored in a common pool to a temporary facility at the site, for storage in dry casks, to create enough space in the pool to store spent fuel taken from the Unit 3 spent fuel pool when that is eventually removed.
At the temporary storage facility, TEPCO will pack the spent fuel in dry casks providing shielding and heat removal (with natural air circulation outside the casks) and store it under stable conditions.
By August, 483 spent fuel assemblies from the common pool will have been transferred to the facility using seven transport and storage casks, in anticipation of the arrival of 566 fuel assemblies (including unused 52 assemblies) from Unit 3.
On May 11, a problem was found at Unit 3—where a fuel handling machine has been in trial operation since March—inside a control panel for a crane used for moving fuel transportation containers to the ground. TEPCO nevertheless aims to begin removing fuel from the spent fuel pool around mid-FY18, as initially planned.
TEPCO will determine a method for removing fuel debris from the first unit by FY19 (April 2019 to March 2020), and the status of that effort was also included in the status report on May 31. The approach is to proceed after heightened understanding is made of internal conditions, the nature of the debris, and the effects when removed.
As that has not yet been fully completed, though, the effort will proceed gradually and incrementally, as follows: first investigating the interiors of the primary containment vessels (PCVs) through sampling, then carrying out small-scale removal of debris, followed by large-scale removal.
As for small-scale fuel removal, one promising method seems to be using a “X-6 penetration” rail to access the interiors of the PCVs (found in all the units) from the side, in order to exchange the control rod drive mechanism (CRDM). That method is already being used for inserting investigation devices into PCVs.
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Coastal nuclear reactor resumes operations, joins 2 units nearby

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The No. 1 to No. 4 reactors (from top to bottom) at the Oi Nuclear Power Plant are seen from a Mainichi Shimbun helicopter, in Oi, Fukui Prefecture, on March 14, 2018.
March 14, 2018
FUKUI, Japan (Kyodo) — Kansai Electric Power Co. restarted Wednesday a reactor at its Oi plant on the Sea of Japan coast, located close to two other units already online, amid lingering safety concerns following the Fukushima disaster.
 
It is the first time that multiple nuclear reactors within the same vicinity have been in operation since the crisis at the Fukushima Daiichi plant, triggered by the March 2011 earthquake and tsunami.
 
The No. 3 reactor at the Oi plant is a mere 14 kilometers from the No. 3 and 4 units at the Takahama plant, all in the central Japan prefecture of Fukui.
 
Local residents are worried about the lack of an effective evacuation plan in the event accidents hit both the Takahama and Oi complexes at the same time.
 
The No. 3 Oi unit is the sixth reactor to resume operations in Japan after clearing stricter safety regulations implemented in the wake of the Fukushima disaster.
 
The government of Prime Minister Shinzo Abe, seeing nuclear power as an “important base-load power source,” is promoting the restart of nuclear reactors considered safe by regulators.
 
Under the current national energy policy, the government plans to generate between 20 and 22 percent of total electricity using nuclear power in fiscal 2030.
 
Kansai Electric aims to start commercial operations of the No. 3 Oi reactor in early April. The No. 4 reactor at the Oi plant is also expected to restart in May, having cleared the Nuclear Regulation Authority’s safety review along with the No. 3 unit in May 2017.
 

Fukushima plant reactor #3 gets new roof cover

 

 
Workers at the crippled Fukushima Daiichi nuclear power plant have finished installing a new roof covering for the No.3 reactor building.
The work started last August to set up a dome-shaped cover. It is part of preparations for removing nuclear fuel from the reactor’s storage pool. A total of 566 spent and unused fuel units remain in the storage pool of the No. 3 reactor.
On Wednesday, workers installed the last part of the cover, which is 17 meters high and 22 meters wide, and weighs 55 tons.
The cover will prevent radioactive materials from spreading, and shield the building from winds.
Reactors at the Fukushima plant suffered meltdowns after a quake-triggered tsunami hit the plant on March 11th, 2011. The fuel units left in storage pools need to be removed as part of decommission work at the plant.
The plant’s operator, Tokyo Electric Power Company, will clear the pool of rubble and provide workers with training on remotely handling devices for the fuel removal.
Then, it plans to start removing nuclear fuel units from the No.3 reactor’s storage pool in autumn this year, ahead of those of other damaged reactors.
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Inside a meltdown-hit Fukushima reactor building

February 17, 2018
Seven years on, Tepco aims to pull fuel out of Unit 3’s rubble-strewn pool
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A crane and dome-shaped roof have been erected on the top floor of Fukushima Daiichi’s No. 3 building, in preparation for removing rods and rubble from the spent fuel pool
 
FUKUSHIMA, Japan — As the Fukushima Daiichi nuclear disaster unfolded in March 2011, a hydrogen explosion ripped through the No. 3 reactor unit. Nearly seven years on, steel framing and other debris still litter the spent fuel pool, along with 566 fuel rods.
The painstaking process of removing the rods is expected to begin sometime in the fiscal year that starts in April. The fuel extraction will be a first for reactor Nos. 1-3 at the Tokyo Electric Power Co. Holdings facility, which was crippled by the earthquake and tsunami that hit northeastern Japan.
On Feb. 8, reporters from The Nikkei were allowed into the No. 3 building to get a sense of the work that awaits. 
A 20-minute bus ride from the town of Tomioka took us to Fukushima Daiichi. After donning masks and protective clothing, we walked toward Unit 3. An elevator slowly lifted us to the top floor of the building, about 36 meters up. There, a crane for moving the spent rods stood ready, wrapped in plastic sheeting. We peered down into the pool but could not see the fuel, which lies under 4 to 5 meters of water.
Large slabs of rubble that fell into the pool have been removed, but smaller pieces remain.
Other decontamination work is proceeding gradually. Radiation on the top floor was measured as high as 2,000 millisieverts per hour in the disaster’s immediate aftermath, but now it is less than 1 millisievert.
Still, caution is a must. Near the pool, our dosimeters displayed relatively high readings of up to 0.7 of a millisievert per hour. “The reading has climbed, so let’s leave for now,” a Tepco supervisor said. As we moved on, we frequently checked to ensure our exposure would not exceed 0.1 of a millisievert a day. 
 
Spent fuel has been removed from reactor No. 4, which was not operating when the tsunami hit the plant. But the job will be a challenge at the meltdown-stricken Unit 3. The rods and rubble will be extracted with heavy equipment operated remotely, from a separate administrative building. 
While it normally takes about two weeks to remove spent fuel, Tepco intends to proceed carefully over the course of two years.

Drone to probe Fukushima N-plant interior

February 10, 2018
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Tokyo Electric Power Company Holdings Inc. plans to use a small unmanned aerial vehicle to closely inspect conditions inside the No. 3 reactor building of the Fukushima No. 1 nuclear power plant as early as this month.
TEPCO will use the drone to examine the location of scattered debris and the level of radiation inside the reactor building, among other things.
It will be the first drone-based research conducted inside the plant’s Nos. 1, 2 and 3 reactor buildings, in which nuclear meltdowns occurred.
The drone, called Riser, was developed by a British company. It measures 83 centimeters by 93 centimeters and weighs about four kilograms.
Riser is equipped with cameras and a dosimeter that can measure up to 2.5 sieverts of radiation per hour.
Even in indoor spaces inaccessible to GPS signals, the drone is capable of determining its position and avoiding obstacles using lasers.
The same model was used for decommissioning work at the Sellafield nuclear facility in Britain.
TEPCO’s plan is for the drone to enter the No. 3 reactor building through a bay for large cargo on the first floor, then fly upward through a series of openings from the first to the fifth floor.
The drone will check areas including the building’s third floor, which has not been sufficiently monitored because radiation levels are too high.
According to TEPCO, key equipment such as that used to cool spent nuclear fuel pools are located on the third floor.
Confirming the location of possible obstacles and the level of radiation is necessary before decommissioning work can progress.
Riser also has a mapping function that enables it to produce three-dimensional graphic images of its surroundings using lasers.
Combining these images with measurements of radiation levels allows for the production of maps outlining contamination levels inside the reactor buildings. TEPCO will consider making this kind of distribution map in the future.
A hydrogen explosion inside the No. 3 reactor building on March 14, 2011, destroyed the building’s upper structures.
Work is currently under way to construct a dome-shaped roof over the building to facilitate the removal of fuel that remains in the spent fuel storage pools.

Installation of a dome-shaped rooftop cover near completion at Unit 3 reactor

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Japan Fukushima Cleanup
In this Thursday, Jan. 25, 2018 photo, an installation of a dome-shaped rooftop cover housing key equipment is near completion at Unit 3 reactor of the Fukushima Dai-ichi nuclear power plant ahead of a fuel removal from its storage pool in Okuma, Fukushima Prefecture, northeast Japan, during an exclusive visit by The Associated Press. The hardest-hit reactor at the Fukushima plant in the March 2011 disaster is moving ahead of the other two melted reactors seven years later in what will be a decades-long cleanup. (AP Photo/Mari Yamaguchi)

Worst-hit reactor at Fukushima may be easiest to clean up

By MARI YAMAGUCHI
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In this Thursday, Jan. 25, 2018, photo, an installation of a dome-shaped rooftop cover housing key equipment is near completion at Unit 3 reactor of the Fukushima Dai-ich nuclear power plant ahead of a fuel removal from… (AP Photo/Mari Yamaguchi)
OKUMA, Japan (AP) — High atop Fukushima’s most damaged nuclear reactor, the final pieces of a jelly-roll shaped cover are being put in place to seal in highly radioactive dust.
Blown apart by a hydrogen explosion in 2011 after an earthquake and tsunami hit Japan’s Fukushima Dai-ichi plant, reactor Unit 3 is undergoing painstaking construction ahead of a milestone that is the first step toward dismantling the plant.
 
The operating floor — from where new fuel rods used to be lowered into the core — has been rebuilt and if all goes as planned, huge cranes will begin removing 566 sets of still-radioactive fuel rods from a storage pool just below it later this year.
 
It has taken seven years just to get this far, but now the real work of cleaning up the Tokyo Electric Power Co. plant can begin.
“If you compare it with mountain climbing, we’ve only been preparing to climb. Now, we finally get to actually start climbing,” said Daisuke Hirose, an official at the plant’s decommissioning and decontamination unit.
Cleaning up the plant’s three reactors that had at least partial meltdowns after the earthquake and tsunami is a monumental task expected to take three to four decades. Taking out the stored fuel rods is only a preliminary step and just removing the ones in Unit 3 is expected to take a year.
Still ahead is the uncharted challenge of removing an estimated 800 tons of melted fuel and debris inside the cracked containment chambers — six times that of the 1979 Three Mile Island accident.
The area in and outside of Unit 3 is part construction site and part disaster zone still requiring protection from radiation. A makeshift elevator, then a wind-swept outdoor staircase, takes visitors to the operating floor, more than 30 meters (100 feet) above ground.
Daylight streams in through the unfinished section of the new cover, a tunnel-like structure sealed at both ends to contain radiation. An overhead crane that moves on rails stands at the side of the storage pool, the maker’s name, “Toshiba,” emblazoned in large red letters.
The explosion left major chunks of debris that have been removed from the storage pool, a painstaking operation done using remote-controlled machinery and with utmost care to avoid damaging the fuel rods. Smaller rubble lines the pool’s edge. The water’s surface is obscured by a blue netting to prevent more debris from accidentally tumbling in.
The severe damage to Unit 3 has, in the end, made it easier to clean up than the other two reactors.
Under the latest government roadmap approved last September, removal of the fuel rods from units 1 and 2 was delayed by three years until 2023, a second postponement from the original 2015, because further decontamination and additional safety measures are needed.
Unit 1 fell behind because of a delay in removing debris and repairing key components on the operating floor. The Unit 2 building remained intact, keeping high radiation and humidity inside, which makes it more difficult for workers to approach and decontaminate.
Radioactivity on the Unit 3 operating floor has fallen to a level that allows workers in hazmat suits and filter-masks to stay up to two hours at a time, though most work still needs to be done remotely.
The segments of the new cover were pre-assembled and are being installed one by one by remote-controlled cranes. With two pieces left, the plant operator says the cover will be completed in February.
Removing the fuel rods in Unit 3 will be done with a fuel-handling crane. It will move the rods out of their storage racks and pack them in a protective canister underwater. A second Toshiba crane, a 10-meter (33-foot) -high yellow structure across the operating floor, will lift the canister out of the pool and load it onto a vehicle for transport to another storage pool at the plant.
Crane operators and others assigned to the project, which requires caution and skill, have been rehearsing the procedures.
The 1,573 sets of fuel rods stored in spent fuel pools at the three reactors are considered among the highest risks in the event of another major earthquake. Loss of water from sloshing, structural damage or a power outage could cause meltdowns and massive radiation leaks because the pools are uncovered.
Hirose said that starting fuel removal at Unit 3 would be “a major turning point.”
Still, after the intact fuel rods are gone comes by far the most difficult part of decommissioning the plant: removing the melted fuel and debris from inside the reactors. Obtaining exact locations and other details of the melted fuel are crucial to determining the retrieval methods and developing the right kind of technology and robots. With most melted fuel believed to have fallen to the bottom, experts are proposing that it be accessed from the side of the containment vessel, not from the top as originally had been planned, based on the cleanup after an accident at the Three Mile Island nuclear plant in the United States.
Computer simulations and limited internal probes have shown that the melted fuel presumably poured out of the core, falling to the bottom of the primary containment vessels. Robotic probes at the Unit 3 and 2 reactors have captured images of large amounts of melted fuel, but attempts so far at Unit 1 have been unsuccessful.
Despite scarce data from inside the reactors, the roadmap says the methods for melted fuel removal are to be finalized in 2019, with actual retrieval at one of the three reactors in 2021. Hirose says it is premature to say whether Unit 3 will be the first.