Tokyo Electric has announced a new plan to attempt to retrieve the fuel handling machine that fell into the Fukushima Daiichi Unit 3 spent fuel pool.
TEPCO has been working to remove the fuel handling machine from the spent fuel pool in parts. Previous attempts to retrieve debris from the spent fuel pool were halted after dislodging debris which fell back into the pool and oil was found to be leaking from some of the parts collected.]]>
Holtec International President Kris Singh told the Vermont Nuclear Decommissioning Citizens Advisory Panel on Friday that the HI-STORM (Holtec International Storage Module) spent nuclear fuel storage casks constructed by his company can withstand cold weather and even being flooded.
Singh asserted that the HI-STORM casks were the best and safest in the world and claimed that each cask would last 300 years — even though the longest a HI-STORM cask has been used in the field is only 15 years.
Each cask is constructed out of stainless steel and high-density concrete. One of the features of the casks is that they don’t have welds, which are prone to leaking. They are designed to withstand high-impact crashes, high temperatures and bullets.]]>
At the L Area Complex in the Savannah River Site (SRS), high and low enriched spent nuclear fuel is stored in underwater storage facilities called disassembly basins. In 1998, Savannah River opted to consolidate all of its spent fuel storage in the L Basin facility.
The L Basin facility has concrete walls, is 17 to 50 feet deep, and holds approximately 3.5 million gallons of water which keeps the fuel rods cool and protects workers from radiation.
Spent nuclear fuel has been filling up the L Basin storage facility, which is nearing capacity. This has forced SRS staff to restart spent nuclear fuel processing operations.
As of 2012, the L Basin facility was storing 3,174 spent nuclear fuel assemblies and had enough room installed for 3,650 assemblies. The facility also held 120 high flux isotope reactor cores which were all it was approved to hold.[i]
Workers at the H Canyon processing facility at the SRS will conduct operations processing up to 1,000 spent nuclear fuel bundles from the Material Test Reactor and 200 offloaded cores of spent fuel from high flux isotope reactors which are currently stored at the site. Fuel from Material Test Reactors can have up to 93% U-235.[ii]
The goal is to employ a chemical process to separate the high-enriched uranium from the spent fuel rods and down blend it with natural uranium to make new fuel rods for commercial nuclear reactors in the United States.
The fission products and plutonium separated from the fuel rods will be transferred to the high level waste system where they eventually will be vitrified into glass at the Defense Waste Processing Facility at Savannah River.
During surveillance of the L Basin in 2011, workers discovered mysterious “cobwebs” covering the tops of spent fuel bundles in the spent fuel pool. Samples were taken and analyzed. The analysis showed that the cobwebs were made up of bacteria and microbes.
Workers tried vacuuming the top of the fuel racks, which had never been done before. Some areas were coated with cobwebs so thick that it took three years for all of them to be removed.[iii]
The Department of Energy still needs to form an official decision on the future of the spent fuel in the L Basin facility, whether to pursue dry storage or continue reprocessing. Analysts from the Savannah River National Laboratory published a study in 2011 which concluded that the spent fuel could be stored at the SRS site for an additional 50 years.
[i] Department of Energy
[ii] Institute of Nuclear Materials Management
[iii] Savannah River Site]]>
At the crippled Fukushima Daiichi nuclear power plant, workers accidentally dropped a large piece of debris into the Unit 3 spent fuel pool on Friday, a little after noon.
The workers were carrying out operations to remove debris with a large remote controlled crane. At the time of the accident, workers were manipulating the control console for the refueling machine, a piece of equipment that weighs almost a thousand pounds.
Tokyo Electric, who is in charge of cleanup operations at Fukushima Daiichi, told reporters that they have not detected any change in radiation levels around the spent fuel pool after the accident.
TEPCO is working to check the 566 spent fuel assemblies in the Unit 3 spent fuel pool to see if any of them have been damaged by the most recent accident. According to decommissioning plans, the utility is scheduled to start removing spent fuel rods from the Unit 3 spent fuel pool in the first half of 2015 at the earliest.
This is not the first time that debris and large objects have been accidentally dropped, pulled, or pushed into the Unit 3 spent fuel pool. Between 2012 and 2013, TEPCO workers used the remote control cranes to remove debris from atop the Unit 3 reactor building, and multiple instances were recorded where operators moving cranes via remote control knocked debris into the spent fuel pool or dislodged other materials on the roof.
In February 2013, workers accidentally knocked the 1.5 ton fuel handling machine mast into the Unit 3 spent fuel pool, and it was later found to have come to rest on top of the spent fuel racks after it narrowly avoided damaging the liner of the spent fuel pool.]]>
Caroline Kennedy, the US Ambassador to Japan, spent three hours visiting the crippled Fukushima Daiichi nuclear power plant on Wednesday as part of her first trip as ambassador to Fukushima Prefecture.
While touring the site, Kennedy observed spent fuel removal operations at the Unit 4 reactor, visited the shared control room for the Unit 1 and Unit 2 reactors, and met with TEPCO officials who discussed how the loss of power was dealt with after the tsunami hit the station on March 11th, 2011.
Kennedy told reporters that it is difficult to fully comprehend the complexity of issues that are being faced just by reading about it.
The ambassador issued a statement committing aid from the United States to decommissioning efforts and specifically helping Japan cope with the highly contaminated water that is piling up onsite and flowing into the Pacific Ocean.]]>
Tokyo Electric, the utility decommissioning the Fukushima Daiichi nuclear power plant in Japan, determined that human error is the most likely cause for the alarms which stopped work removing spent fuel assemblies from the Reactor 4 spent fuel pool.
TEPCO officials believe that around 9:30 AM on Wednesday, a worker attempted to operate a crane to remove a spent fuel cask which had been loaded with 22 spent fuel assemblies from the spent fuel pool while an auxiliary brake was applied.
Because the brake was on, excess current was directed to the motor of the crane, which locked operations and set off an alarm.
The worker noticed the problem and attempted to correct it by releasing the brake and retried the crane, but the motor would not operate after the alarm had been activated.
According to the utility, the crane motor was not damaged as a result of the error.
Workers are reviewing the work process and will likely resume work operations soon.]]>
Workers at the Fukushima Daiichi nuclear power plant have been forced to halt removal of spent fuel rods from the Reactor 4 spent fuel pool.
The pool contains 1,533 fuel rods, 1,331 of which are highly radioactive spent fuel rods. As of Wednesday, 550 fuel rods have been retrieved from the spent fuel pool.
Around 9:30 am on Wednesday, while workers were attaching a hook to a large crane to retrieve a cask containing 22 spent fuel rods from within the pool, an alarm sounded and forced the work to come to a halt.
The utility is still working to determine the cause of the problem, but report that they have not detected an increase in radiation levels around the pool.]]>
In the three years since the start of the Fukushima Daiichi nuclear disaster there has been a plethora of drastic changes made to the landscape of the Fukushima Daiichi nuclear power plant including; new processing facilities for radioactive water, a farm of storage tanks for contaminated water, new cooling systems, a new carpet of thick steel sheets for most of the grounds around the crippled reactor buildings, new coverings and support structures for the damaged reactor buildings, and a new decommissioning facility, but little progress made in the decommissioning operation.
Over 430,000 tons of highly radioactive water is estimated to be stored at the Fukushima Daiichi site, in some 1,000 storage tanks. TEPCO is working to increase its storage capacity to 8000,000 tons, but the problem is that storing the contaminated water in above-ground tanks risks leaving them vulnerable to other threats, like earthquakes and accelerated wear.
Contaminated water continues to pile up every day at the Fukushima Daiichi site. Over 1,000 metric tons of groundwater flow down the mountain side of the Fukushima Daiichi site, through the grounds of the facility, and into the Pacific Ocean. An estimated 400 tons pass through the crippled reactor buildings themselves, coming in contact with the melted nuclear fuel and becoming contaminated, before continuing their journey into the ocean. Approximately 100 tons of this radioactive water is captured each day and held in storage tanks, but room for storage on-site is quickly running out and there have been repeated problems with leaks.
Some of the leaks have released enough radioactive materials into the environment to be classified as a level three incident on the International Nuclear Event Scale (INES), which measures incidents on a scale of 0 to 7. As the volume of contaminated water increases, so do the problems with processing and storage, which draws concern among experts who fear that the problems stemming from managing the radioactive water at the tank farm will only increase in the future.
While Tokyo Electric, the utility which owns and operates the Fukushima Daiichi plant, has started removing fuel assemblies from the Unit 4 reactor, they still face an uphill battle with the day to day management of the facilities. Repeated leaks of radioactive materials and almost daily accidents have undermined much of the faith and support in TEPCO’s ability to see the decommissioning project through to completion.
Tokyo Electric’s roadmap for decommissioning, which was created by the central government and TEPCO, outlines three phases. The first phase includes all spent fuel removal operations at all Units 1-4. The second phase is by far the most difficult as it includes all work to remove the molten nuclear fuel from Units 1-3. The third phase signals the completion of fuel removal operations and includes work to dismantle the crippled reactor buildings.
One of the most important variables in whether decommissioning will progress on schedule or not is whether TEPCO can supply enough technical staff and workers, before they exceed their permitted radiation exposures or pursue work at other nuclear facilities. Repeated incidents at the site have been caused by human error, and these incidents will only increase as the experience and proficiency of workers on-site decreases.
Currently, TEPCO is working on removing the spent fuel rods from the Unit 4 spent fuel pool. At the time of the earthquake and tsunami there were 1,331 spent fuel assemblies and 202 new fuel assemblies stored in the spent fuel pool. As of March 3rd, TEPCO has removed over one quarter (418) of the 1,533 total assemblies, 396 spent fuel assemblies and 22 new fuel assemblies. The utility plans to have the Unit 4 spent fuel pool emptied by the end of the 2014. TEPCO estimates it will start removing the 1,573 total spent fuel rods from the Unit 1-3 spent fuel pools in 2015 for Unit 3 and 2017 for Unit 1 and Unit 2.
Some readers may not realize why the second phase will be so difficult. Aside from the fact that no current technologies will assist in removing the extremely radioactive melted fuel rods due to the high levels of radiation, that workers cannot enter critical areas of the reactor buildings due to the same high levels of radiation, and the fact that no one knows where the melted reactor fuel is currently located or what condition it is in – in all three of the reactors, there is also a problem of the sheer volume of melted materials which must be removed from Units 1-3. While there were 1,533 spent fuel rods in the Unit 4 spent fuel pool, there were also 1,496 fuel rods believed to be in the reactors of Units 1-3. The majority, if not all, of these fuel rods are believed to have melted. In order to remove melted fuel from the containment vessels, workers must fill them with water to reduce radiation levels, but this will require an enormous amount of work restoring the containments to make them capable of holding the water.
If TEPCO is capable of keeping up with the decommissioning roadmap, it still will not start removing the melted fuel from the Unit 1 and Unit 2 reactor buildings until 2020, and the Unit 3 reactor building in 2021. However, seeing as Tokyo is hosting the Summer Olympics in 2020, it is hard to believe that TEPCO will attempt much, if any, fuel extraction operations before the Olympic Games.
Tokyo Electric also decided to decommission the Unit 5 and Unit 6 reactors on January 31st, 2014. These units were not damaged in the earthquake and tsunami, but it is thought that decommissioning these reactors will help train workers and aid TEPCO in planning to decommission the damaged reactors.]]>
The Rokkasho Reprocessing plant consists of nearly 40 buildings, including a nuclear waste monitoring facility, a MOX fuel fabrication plant, a uranium enrichment plant, and a radioactive waste landfill. In 2008, experts disclosed that the Rokkasho facility is sited directly above an active geological fault.
Regulators are interested in establishing a better understanding of the underground structures and information related to a potential offshore fault.
Japan Nuclear Fuel will also have to explain how it reviewed its estimates for earthquake and volcano activities following the Fukushima Daiichi nuclear disaster and the government’s new safety guidelines.
Some of the problems that Rokkasho faces are unlike typical nuclear power generation stations. There are disasters like fires, explosions, chemical leaks, among others, which are much more hazardous at a reprocessing facility.
The licensee has told the media that it hopes to have the reprocessing facility ready for operation by October of 2014, but it remains to be seen if regulators will have finished their safety screenings by that time.
Even if the Rokkasho facility was brought online, it would still be unable to keep up with the waste generated by the nuclear reactors in Japan. The facility already hosts more than 3,000 tons of spent fuel in its spent fuel pols, which are already 95% full.
If the Rokkasho plant were to be closed, it would be forced to return the nuclear waste it currently stores back to the Japanese utilities which produced it, but spent fuel pools at nuclear power stations in Japan are already 70% full on average.]]>
April 20th, 2011 – JNES Assessment of Spent Fuel Pool at Fukushima Daiichi Unit 4 – Pages from C146301-02X…]]>
On Monday at 15:18, TEPCO workers began work removing spent fuel from the crippled Fukushima Daiichi Unit 4 spent fuel pool, which holds 1,533 assemblies. Of the 1,533 assemblies, 1,311 are spent fuel, the other 222 are unused.
This project has been labeled by some as one of the most dangerous nuclear operations in human history. Experts all agree that the engineering challenges are on a scale unseen to date.
Workers are removing the unused assemblies first, as they do not emit as much radiation and heat as the spent fuel assemblies.
Each spent fuel assembly is made up of about 80 fuel rods, which by assembly can contain up to 7,500 trillion becquerels of radioactivity and around 1% plutonium by weight.
The 2013 World Nuclear Industry Status Report claims that the “full release from the Unit-4 spent fuel pool, without any containment or control, could cause by far the most serious radiological disaster to date.”
Work will be challenging, due to the amount of debris in the spent fuel pool from the March 2011 explosion, which ripped the building asunder.
Workers will discover new damage to fuel units they were unaware of previously. The pieces of debris from the explosion were ejected with enough force to potentially damage fuel rods or jam multiple assemblies together.
The assemblies could also be moved too close together. The spent fuel rods could break, or be exposed to air and potentially ignite; both scenarios would potentially release a massive amount of radiation, which could necessitate the evacuation of workers from the plant.
According to Bloomberg, if the rods were to overheat or break, a self-sustained nuclear chain reaction similar to the meltdowns in the crippled reactors could be prompted.
The spent fuel assemblies are gripped by a huge remote-controlled crane and transferred into dry cask storage containers which each can hold up to 22 assemblies. Moving the first assembly into the cask took workers more than an hour.
Once the storage cask is full, workers will lift the container out, load it onto a trailer, and move it to the central repository. Work is largely carried out at a slow crawl. The movement of one cast out of the pool takes 12 hours over a 48-hour period, and 8 to 10 days to complete transfer to the new storage pool.
Tokyo Electric plans to finish removing all the spent fuel from the Unit 4 reactor building by the end of 2014.
Many experts have brought to light their concerns related to another major earthquake striking Japan near the Fukushima Daiichi site while workers are conducting removal work.
Estimate time for boil-dry times for a typical spent fuel pool
Source: RTM Table D-1 (see figure below)
(1) Full core recently discharged (see box in figure)
(2) 100 days after shutdown (full core unloaded)
(3) constant decay heat at 100 days on
(4) Neglect sensible heating from the table (- 10 hr)
(5) No water loss from the pool thru leaks, water spillage, explosion, etc.
Time since accident = – 5 days
Time to boiloff (Table D-1) = 164 hr = 6.8 days
Assuming pool at 100% 5 days ago and it takes 6.8 days to boil off, after 5 days about 75% (5/6.8) of water has boiled off with 25% remaining.
Time to boil-off remaining 25% = 0.25 x 164 hr = 40 hrs => this is the maximum time left considering assumption 5 above.
March 16th, 2011 – Estimate Time for Boil-dry Times for a Typical Spent Fuel Pool by Enformable]]>
Monday night, a power outage at the Main Anti-Earthquake Building at the Fukushima Daiichi nuclear power station suspended operations at three spent fuel pool cooling systems and other critical plant facilities. TEPCO was later criticized for a three hour delay between the power outage and their notification of the event to the press.
After further investigation, TEPCO announced that the switch gear in the process building, common fuel pool, and Unit 3 and Unit 4 switchgear had been found to be not operable. Workers were unable to determine what caused the boards to stop functioning, as no visible damage was found. They later repaired two of the boards, but are currently using an emergency power generator to restore cooling for the Unit 4 spent fuel pool while the Unit 3 spent fuel pool and common fuel pool are still not restored.
“We are still trying to identify the cause (of the power loss). We need to investigate further,” said Tepco executive Masayuki Ono, who served as spokesman at the news briefing Tuesday morning.
The blackout not only raised concerns about the resilience of the ad hoc cooling systems, but affected multiple critical systems, including the Kurion Cesium adsorption system at the water treatment facility, the Unit 3 and Unit 4 spent fuel pool primary and secondary cooling systems, the Unit 3 PCV gas control system, and the Common fuel pool cooling and purification system. Additionally, TEPCO found that the Unit 1 spent fuel pool alternative cooling system and the Nitrogen separator system were not operating, though not due to the switch gear problems.
The Unit 4 spent fuel pool (1,533 spent fuel assemblies) and the Common fuel pool (6,377 spent fuel assemblies) both house enough spent fuel pool assemblies that the decay heat still given off is capable of heating up over 40 degrees in less than a week. The Unit 4 spent fuel pool has the highest temperature increase rate, due to the full core offloaded in the already over-packed fuel pool, two to four times faster than that Unit 1 and Unit 3 spent fuel pools.
Source: The Japan Times]]>
According to TEPCO and the Japanese Nuclear Regulation Authority, around 19:00 on Monday night, the seismic building at the Fukushima Daiichi nuclear power plant had experienced a power failure. While the outage did not affect the monitoring instruments in the reactor containment, it did affect the spent fuel pool cooling system at Unit 1, Unit 3, and Unit 4.
TEPCO data shows that the Unit 4 spent fuel pool was at the highest temperature at the time of the outage, but has a margin of about four days before the temperatures would be expected to reach levels of concern. The contaminated water treatment system was also knocked out by the power failure.
TEPCO workers are still investigating the cause of the outage.
Source: The Daily Yomiuri]]>