New proposal suggests removing Fukushima plant’s melted nuclear fuel from side — The Mainichi

” A method to remove melted nuclear fuel debris on the bottom of the containment vessels of Fukushima No. 1 Nuclear Power Plant’s first, second and third reactors from the side was proposed by the Nuclear Damage Compensation and Decommissioning Facilitation Corporation (NDF) on July 31.

Hajimu Yamana, head of the NDF, which is tasked with considering how to remove fuel debris from the reactors, for the first time explained the organization’s specific method proposal to the heads of local governments at a countermeasures for the decommissioning and handling of the contaminated water council meeting held in Iwaki, Fukushima Prefecture.

The method would focus on prioritizing the removal of debris from the bottom of the vessels from the side, using robotic arms and other remote devices while flushing water over the debris. However, ways to block radiation and countermeasures against the scattering of airborne radioactive dust still remain unsolved. The central government and Tokyo Electric Power Co. (TEPCO) plan to finalize their policy to remove the debris and amend the decommission schedule in September.

In all three of the reactors, contaminated water has collected at the bottom of the containment vessels. The NDF had previously considered a “flooding method” that would fill the containment vessels completely with water to block radiation from leaking. However, measures to repair the containment vessels and prevent leakage of the radioactive water would be difficult, so the plan was put aside for having “too many issues.” “

by The Mainichi



Japanese robot probes the radioactive water at Fukushima’s nuclear reactor to find melted fuel — Daily Mail

” A Japanese robot has begun probing the radioactive water at Fukushima’s nuclear reactor.

The marine robot, nicknamed the ‘little sunfish’, is on a mission to study structural damage and find fuel inside the three reactors of the devastated plant.

Experts said remote-controlled bots are key to finding fuel at the dangerous site, which has likely melted and been submerged by highly radioactive water.

The probe – about the size of a loaf of bread – is equipped with lights, manoeuvres using tail propellers and collects data using two cameras and a dosimeter radiation detector.

Plant operators chose to send the robot inside the containment vessel of the No. 3 reactor because it has highest known water levels out of the the three reactors.

The robot entered the structure at 6.30am JST (10.30 BST, 5.30 ET) through a pipe connected to the containment vessel.

The marine machine, which was attached to cables, then swam to the area just below the reactor pressure vessel inside to take images.

New images taken by the robot show how parts of the system, including the control rod, have been damaged by radiation.

On Friday, the robot will continue its travels to the bottom of the containment vessels, where melted fuel deposits are believed to have accumulated.

In 2011, a 10-metre-high tsunami that killed nearly 19,000 people crashed into Japan’s Fukushima nuclear power plant, leading to several meltdowns.

Five years after the disaster, researchers are still struggling to clean up the highly dangerous radioactive materials in water of the wasting reactors.

It’s estimated that plant officials have only located 10 per cent of the waste fuel left behind after the nuclear meltdowns.

And the damaged plant is believed to be leaking small amounts of the radioactive waste into the Pacific Ocean, which could be travelling as far as the west cost of the US.

Researchers are now pinning their hopes on the remote-controlled sunfish robot to locate the lost fuel in order to work out the safest way to remove it.

During a demonstration of the device at a test facility near Tokyo last month, the probe slowly slid down from a rail and moved across the water.

A team operated it remotely, with one guiding the robot while another adjusted a cable that transmits data and serves as its lifeline.

Japan hopes to locate and start removing fuel from the reactors after Tokyo’s 2020 Olympics.

In earlier operations, snake and scorpion-shaped robots became stuck inside two reactors.

The scorpion robot’s crawling function failed and it was left inside the plant’s Unit 2 containment vessel.

The other, designed for cleaning debris for the ‘scorpion’ probe, was called back after two hours when two of its cameras stopped working after its total radiation exposure reached 1,000 Sievert – a level that would kill a human within seconds.

The plan had been to use the robot for 10 hours at an exposure level of 100 Sievert per hour.

The swimming robot shown was co-developed by electronics and energy giant Toshiba and the government’s International Research Institute for Nuclear Decommissioning. “

by Daisy Dunne, Mail Online and Associated Press

source with photos and video

Tepco delays robotic surveys at Fukushima nuclear reactors — The Asahi Shimbun

” Tokyo Electric Power Co. has postponed inspections by robots to finally confirm the location and state of melted fuel at two damaged reactors of the Fukushima No. 1 nuclear plant.

The camera-equipped robots were scheduled to enter the containment vessels of the No. 1 and No. 2 reactors within fiscal 2015, which ends in March. But TEPCO said Jan. 28 that a series of unexpected circumstances, such as poor visibility caused by murky radioactive water, have ruined that plan.

The robot for the No. 1 containment vessel will be redesigned, and the remote-controlled survey will be conducted in fiscal 2016, the utility said, without offering a more specific timetable.

Nuclear fuel assemblies in the No. 1 to No. 3 reactors are believed to have melted and fallen to the bottom of the containment vessels following the March 2011 earthquake and tsunami.

Radiation levels inside the containment vessels remain extremely high, making them too dangerous to be approached by workers.

The remote-controlled robotic probe was seen as crucial in determining conditions inside the containment vessels for the eventual decommissioning of the nuclear plant.

TEPCO conducted a preliminary survey using an industrial endoscope in the containment vessel of the No. 1 reactor. It found accumulated waste turned the water murky and blocked the view.

For the No. 2 reactor, TEPCO had planned to locate the melted nuclear fuel using a robot last summer. But decontamination and cleanup work near the entrance to the containment vessel proved difficult. That prevented TEPCO from carrying out robotic survey as planned. ”

by Hiromi Kumai


Salt in the wound — Arnie Gundersen, Fairewinds Energy Education

” What really happened to the Fukushima Daiichi reactors when workers from owner Tokyo Electric Power Company added ocean saltwater to cool them?

Fairewinds recently received this question and important technical comments from several viewers and engineers regarding utility owner TEPCO’s use of saltwater to cool the Fukushima Daiichi atomic reactors during their triple meltdowns. As we continue looking at aging operating atomic reactors around the world, it is important to understand this issue and know what may go wrong at other sites.

Listen as Fairewinds’ Chief Engineer Arnie Gundersen explains why TEPCO’s workers injected saltwater into Fukushima’s failing reactors, what happens when salt water meets steel, and what forces come into play after saltwater is used to cool down an atomic reactor in this Fairewinds Audio Update. ”

source with audio and transcript

More reactors expected to be restarted in western Japan — Nikkei Asian Review

” TOKYO — The Sendai No.1 reactor, Japan’s first active reactor in about two years, has resumed full-scale commercial operations. As safety screening progresses, other suspended reactors are expected to follow, but mostly in the western part of Japan.

All 43 reactors in Japan are light-water models. “Light water” simply means normal water. Light-water reactors are further categorized into boiling-water and pressurized-water types.

Boiling-water reactors generate steam inside the reactor by boiling water inside, while pressurized-water reactors heat water inside the reactor by adding pressure and sending the heated water to a steam generator.

Nuclear plants in western Japan, including the Sendai plant operated by Kyushu Electric Power, typically have pressurized-water reactors. These include the Takahama Nos. 3 and 4 reactors in Fukui Prefecture, operated by Kansai Electric Power, and the Ikata No. 3 reactor in Ehime Prefecture, run by Shikoku Electric Power. All of these have also passed the new safety screening process.

In contrast, many nuclear facilities in eastern Japan have boiling-water reactors, including the Fukushima Daiichi nuclear power plant that suffered three meltdowns after the earthquake and tsunami of 2011.

Currently, 10 boiling-water reactors at eight plants across Japan are being screened.

Japan’s Nuclear Regulation Authority in July 2013 began reviewing what safety measures suspended reactors would have to take before being cleared to start up again. Nuclear plants with boiling-water reactors were generally slow to apply for reviews because of the time it took to bring their containment vessels up to the new standards.

Reactors reside in these vessels, which are designed to keep radioactive substances inside. After the earthquake and tsunami, the fuel rods inside the Fukushima Daiichi reactors could not be cooled. As a result, they began to melt, releasing massive amounts of radioactive substances.

If the containment vessel does its job during an accident, these substances will not leak into the surrounding environment. Since it is an important job, the nuclear power regulator is making sure new measures to protect the vessels are up to the task.

Containment vessels are made of solid steel and concrete. Even these building materials, however, can give way to extreme inner pressure. When fuel rods cannot be cooled for a prolonged period, the heat they generate turns surrounding water into vapor, a process that generates hydrogen as a byproduct. If enough hydrogen accumulates, it can break through the containment vessel.

Containment vessels for pressurized-water reactors are generally much larger than those around their boiling-water cousins. For example, the containment capacity of the Mihama No. 3 pressurized-water reactor in Fukui Prefecture is 10 times that of the Fukushima No. 3 boiling-water reactor.

Both reactors put out similar amounts of power.

Bigger containment buildings can tolerate the buildup of more inner pressure. Since boiling-water reactors have less containment ability, the regulator has asked their operators to take preventive measures.

As a result, many operators of boiling-water reactors are mulling whether to install filtered vents — special pieces of equipment that can release gas to reduce pressure. When steam is released through these vents, it is filtered to remove most radioactive substances.

For the Nos. 6 and 7 reactors at the Kashiwazaki-Kariwa plant in Niigata, filters are expected to be able to remove more than 99.9% of radioactive particles such as cesium and more than 98% of radioiodine gas.

Filtered vents are only opened in worst-case, last-resort scenarios.

“Basically, we do not expect to use the measure,” said Tadayuki Yokomura, who is in charge of operating the Kashiwazaki-Kariwa plant.

The plant is also installing a worst-case, second-to-last-resort system — one meant to turn steam back into water, which would help to reduce the inner pressure. Pipework for the system is now being prepared.

The regulator seems to be completing the screening of some boiling-water models. But even after passing the tests, a suspended reactor cannot restart without the consent of the municipal government where it resides and other relevant bodies.

And that could prove to be an even taller hurdle than passing the new tests. More than four years after the meltdowns, many Japanese remain skeptical about nuclear reactor safety. ”


Editorial: No more half-baked plans for decommissioning Fukushima reactors — The Asahi Shimbun

” For the first time in two years, the government and Tokyo Electric Power Co. have announced a revised mid- to long-term road map for decommissioning nuclear reactors at the crippled Fukushima No. 1 power station. The removal of spent nuclear fuel from storage pools at the No. 1, No. 2 and No. 3 reactors will be delayed by up to three years.

The government and TEPCO explained this delay is due to their new policy of “risk reduction over speed.”

This delay, right from the start, must mean that the old road map was poorly planned.

Are the government and TEPCO really able to now foretell that the delay will be three years at most? And why was risk reduction not their top priority until now?

The government and TEPCO must draw concrete lessons from all the delays to date and apply the lessons to the long-term decommissioning road map.

Spent nuclear fuel in the fuel pools must be removed to a safe place as soon as possible. Delays in its removal are caused by the time-consuming preparatory work of debris removal and decontamination of workspace floors.

In autumn 2013, Prime Minister Shinzo Abe declared in his 2020 Olympics bid speech that the situation was “under control.”

Since then, it has become abundantly clear that the situation is anything but under control, and that the previous decommissioning road map failed to accurately assess the high level and extensive spread of radiation contamination.

Removing debris releases radioactive substances into the atmosphere, possibly causing them to spread beyond the plant grounds. Delays in decontamination expose workers to higher doses of radiation and limit their working hours.

Although nobody knew the amount or exact location of melted fuel in the reactors, the old road map indicated the “flooding method” of removal, meaning the containment vessels of the No. 1, No. 2 and No. 3 reactors were to be filled with water. This method is similar to the usual removal method.

But probing the conditions of the containment vessels by various means revealed the difficulties of stopping the water leakage and problems regarding earthquake-proofing. It is only natural that the new road map proposes to reject the flooding method for the time being and study other removal methods over the next two years.

What we do not understand is why the government and TEPCO continued to reject the recommendation of outside experts to study the matter more broadly.

Last month, TEPCO announced the “completion” of processing a massive amount of highly contaminated water that had collected in clusters of storage tanks. But work is still continuing on separating radioactive substances from about 300 tons of highly contaminated water, which is generated every day. Any water still contaminated by unremoved tritium continues to remain in the tanks.

The decommissioning of reactors after a nuclear disaster is a truly challenging task that Japan has never experienced before.

The government and TEPCO must proceed by prioritizing risk reduction while explaining the situation to the local communities and the nation at large to win their understanding of the decommissioning work itself. ”