Editer l'article Suivre ce blog Administration + Créer mon blog
Le blog de fukushima-is-still-news

information about Fukushima published in English in Japanese media info publiée en anglais dans la presse japonaise

Decommissioning large reactors for the first time

JAPAN: Dismantling of large-scale nuke plants begins at last





August 11, 2013

The Asahi Shimbun GLOBE

At Chubu Electric Power's Hamaoka nuclear power plant in Omaezaki, Shizuoka Prefecture, preparations are being made to dismantle and remove the first and second of its five reactors.

"Move the apparatus!" "You got it!" The voices of workers echo around the inside of the structure that houses the second reactor. An 88-ton carbon steel cylindrical capsule more than six meters long is suspended from a crane and slowly lifted 26 meters to the fifth floor.

Twenty-two spent nuclear fuel units held in a pool on the fifth floor are collected into the capsule. Then the capsule is moved in a purpose-built trailer to the pool for the fifth reactor, which is located within the same site. The capsule has screw-like grooves carved into them to allow the heat produced by the fuel to escape.

Yoshiaki Shimizu, 55, the decommissioning project's group chief, says no radiation would leak out if a capsule fell to the floor during the operation.

"What's more, we have devices on standby just in case that will prevent radiation from leaking outside," he says.

If spent nuclear fuel is not extracted from the inside of a reactor, it cannot be taken apart. The extraction process is fraught with danger due to the potential of radiation exposure to workers and radiation leaks. Large capsules are used, and the process is carried out cautiously.

When the second reactor ceased operating in 2009, there were 1,312 nuclear fuel units held in the fifth floor pool. The transfer of just one took several days, and 724 were left as of late June. The operation will end by late February 2014 at the earliest. The pool for the first reactor has already been emptied.

A number of workers measured the radiation level inside the structure housing the second reactor. They spent several months checking 10,000 spots to create a contamination map of the entire facility. The careless destruction of a structure in a radiation controlled area would be disastrous.

To date, five of Japan's key nuclear reactors have ceased operations in order to be decommissioned, including the two reactors at Hamaoka. The dismantling and removal of the 12,500-kilowatt Japan Power Demonstration Reactor at Tokaimura, Ibaraki Prefecture, was completed in 1996. Currently, the Japan Atomic Power Co. (JAPC)'s 166,000-kilowatt Tokai Power Station at Tokaimura and the Japan Atomic Energy Agency (JAEA)'s 165,000-kilowatt Fugen advanced thermal reactor prototype in Tsuruga, Fukui Prefecture, are in the midst of being decommissioned.

The Hamaoka plant's first (540,000 kilowatts) and second (840,000 kilowatts) reactors are much larger than its other three. Additionally, the reactors that are being decommissioned and those that are scheduled to continue operating are on the same site. Such a case is the first for Japan.

"Our staff will be able to experience running a reactor at the same time as being involved in shutting another down," says Motonori Nakagami, 55, a group chief in Chubu Electric Power's nuclear power division.

The decommissioning process is running slightly behind schedule. This is because many of the approximately 2,300 staff that were to be involved in shutting down the first and second reactors have been preoccupied with inspections of the third, fourth and fifth reactors, which have been stopped since the accident at the Fukushima No. 1 nuclear power plant.

The combined cost of decommissioning the first and second reactors has been estimated at 84.1 billion yen ($840.8 million). It will be a lengthy endeavor, taking nearly 30 years. Throughout that period, their functions that prevent radiation leaks will continue to be maintained, and the structure itself will be constantly repaired as it is used.

The decommissioning of the Tokai reactor, which ceased operating in 1998, is at a more advanced stage. All of its spent nuclear fuel has been removed, and the surrounding apparatus is being dismantled as the JAPC waits for the radiation level inside to go down.

The disassembly of the reactor's four heat exchangers began in 2006. These cylinders, 25 meters tall and six meters in diameter, are being taken apart by slicing them into rings from the bottom up and removing them one at a time. Workers observe from a separate room as a French-made robot cuts into the cylinders. The dismantling of the reactor will begin from fiscal 2014, and the entire process is scheduled for completion in fiscal 2020.

Power companies want to minimize decommissioning costs as much as possible. "Rather than developing new apparatus, we're using a combination of technology that's already available to us to rationalize the process," says JAPC division manager Toyoaki Yamauchi.

Cost reduction is also a priority for the decommissioning of the Fugen reactor. According to the JAEA's Shigetoshi Iwanaga, 59, "We're drawing on foreign expertise as we consider the cheapest way of taking it apart."

(The first part of this article was written by GLOBE writers Norito Kunisue and Hitoki Nakagawa.)


The worst nuclear disaster in history occurred in April 1986 at the Chernobyl plant in Ukraine. Its fourth reactor exploded during a test run, releasing 5,200 quadrillion becquerels of radioactive material in the first 10 days, roughly sixfold that of the accident at the Fukushima No. 1 nuclear power plant.

Just as with ordinary nuclear plants, the disassembly and removal of the reactors that caused these catastrophes cannot begin until their nuclear fuel is extracted.

Even today, 27 years after the Chernobyl accident, the fourth reactor still contains nuclear fuel that has melted and solidified. It produces a level of radiation that would instantly kill anyone who approached it, and cannot be touched until a suitable robot is developed. Extraction will be impossible for quite some time, and the reinforced concrete “stone coffin" that entombs the structure and prevents radiation from leaking out is the only measure that can be taken at present.

Today, crevices and cracks can be found all over the stone coffin. Rainwater that has flowed inside in large amounts is thought to have become contaminated and started leaking into the earth. A major repair effort was carried out from 2004 to 2008, reducing the threat of collapse for the time being. Construction is proceeding on a massive shelter that will cover the stone coffin in order to carry out more permanent countermeasures. There are plans to tear down the stone coffin and remove the nuclear fuel when the shelter is completed in 2015, but there is no concrete schedule.

* * *

Tokyo Electric Power Co. has made a decision to decommission reactors No. 1 through No. 4 at its Fukushima No. 1 nuclear power plant.

TEPCO and the Japanese government are planning to extract the nuclear fuel that is thought to have burned through pressure vessels within reactors No. 1 through No. 3 and remove the structures surrounding them. Thirty to 40 years later, the site will be turned into a vacant lot.

On June 27, the government and TEPCO revised their mid- to long-term decommissioning road map. With regard to when the fuel in reactors No. 1 through No. 3 would be extracted, it states that work on reactors No. 1 and No. 2 will begin in the first half of fiscal 2020 at the earliest, and on reactor No. 3 in the latter half of fiscal 2021. This meant that the extraction process for reactors No. 1 and No. 2 will commence around 18 months earlier than was initially planned.

In reality, there is no technical evidence to support these projections. As a form of “insurance," the plan also states that the commencement date will be shifted back to the first half of fiscal 2024 in the event that little technological progress is made.

To extract nuclear fuel, it is necessary to fill a reactor with water to block the radiation. For that purpose, the damage the reactor has sustained must first be ascertained and then repaired.

It is not yet known where and to what degree it is damaged, or the condition of the fuel that is thought to have burned through its vessels. Surveys were attempted using a remotely controlled robot, but to little success.

Some melted fuel escaped from its pressure vessel and burned through into the containment vessel. There are three reactors where this has occurred, and a wide range of experts will have to pool their knowledge and devise countermeasures in order for the decommissioning process to move forward.

However, more than two years on from the disaster, the system in place for developing fuel extraction technology is still inadequate.

* * *

The second reactor at the Three Mile Island nuclear plant near Middletown, Pa., where a partial meltdown occurred in March 1979, has not yet been dismantled and removed. Even so, the process is at a more advanced stage than at the Chernobyl and Fukushima No. 1 plants.

Several years after the accident, camera inspections of the reactor core commenced, and a work program was carefully devised with input from the nuclear industry, the government and academia. Fuel extraction began in 1985, and by 1990, almost all of it was successively removed. Around half of the fuel was said to have melted through.

Meanwhile, the station's first reactor, located on the same site, has been approved for operation until 2034 and continues to run. To efficiently decommission the reactors, the second will be disassembled at around the same time as the first. The process itself will not begin in earnest for some time down the road.

(The Ukraine portion of this article was written by Naoatsu Aoyama, GLOBE staff writer, and Hisashi Hattori, senior staff writer of The Asahi Shimbun.)


GERMANY: Know-how from a leader in nuclear power abandonment


August 11, 2013




The Asahi Shimbun GLOBE

The Greifswald nuclear power plant on the shore of the Baltic Sea in northern Germany is a three-hour drive from Berlin on the Autobahn.

During its operational phase when East Germany existed, the plant provided 10 percent of the electrical power consumed in the former German Democratic Republic. Today, it is entering the final stage of the decommissioning process.

Reactors No. 1 through No. 5, each once capable of generating 440,000 kilowatts of power, were shut down by 1990 due to rising concerns about the safety of Soviet-designed plants following the 1986 Chernobyl nuclear power plant accident.

Decommissioning of the plant started in 1995.

“Of the 30 steam generators, eight have been completely dismantled. We are deliberately taking our time. The work proceeds as we thoroughly sort and classify waste matter," said Gudrun Oldenburg, deputy head of the PR Department for EWN, a government-funded entity that is responsible for the cleanup.

Most of the equipment in the buildings, such as the reactors, turbines and steam generators, has been moved to an interim storage site on plant grounds. Within the expansive 20,000-square-meter storage facility, which looks like a huge warehouse, the temporarily transferred equipment has been arranged into orderly lines. Radiation levels beside the reactor parts read 50 microsieverts per hour. This is about the same reading as high-dose areas around the Fukushima No. 1 nuclear power plant.

In the work area, employees in coveralls and wearing protective masks labored to disconnect pieces of machinery, their cutting tools creating a shower of sparks. Equipment from inside the reactors is dismantled inside an isolated booth using tools that are operated remotely. In a different booth, workers in protective clothing resembling space suits sprayed equipment with water and an abrasive agent to decontaminate it.

“We have more than 20 years of accumulated experience in the decontamination and management of waste, more than any other nuclear power plant. We are happy to offer our skills and technology to anyone," said EWN's plant manager Henry Cordes.

The company has assisted with dismantling work at the Chernobyl nuclear power plant and other plants in Eastern Europe. Since 2002, it has been helping to dismantle Russian nuclear submarines.

After the accident in Chernobyl, anti-nuclear sentiment spread among the German people, and old nuclear power plants and those with poor profitability were slated for decommissioning. As Germany has been at the forefront of decommissioning nuclear reactors in Europe, it has accumulated know-how that allows it to dismantle and remove nuclear plants safely and efficiently.

After the accident at the Fukushima plant, the Merkel-led government decided to abandon nuclear power generation altogether and revoked operating licenses for eight plants. The nine remaining in operation will lose their licenses by 2022. As decommissioning increasingly spreads, companies will be looking to acquire more technology.

Next year, decommissioning will be completed on the Wurgassen nuclear power plant (670,000 kilowatts) operated by E.ON, a leading gas and power company. The work started in 1997, and 10,000 drums of waste matter are stored at a temporary facility constructed on the site's premises.

The company plans to move the drums to a disposal site that the government intends to construct by 2019. Manfred Winnefeld, the E.ON's plant manager, said: “Decommissioning was supposed to be completed in roughly 10 years. However, work did not proceed as smoothly as envisioned and in 2003 the schedule was revised substantially."

Even so, completing the work in roughly 16 years is quick when compared to other nuclear plants, he added.

In June, E.ON established a decommissioning business.

Erich Gerhards, senior vice president in charge of dismantling and disposal, said, “We would like to sell our process and management know-how, which has been built through extensive experience, including failure, to the global market."

(The first part of this article was written by Hisashi Hattori, senior staff writer of The Asahi Shimbun.)


Wearing 3D glasses, I stood in front of a large screen roughly 2 meters high and 4 meters wide. The power generator projected onto the screen drew increasingly nearer. Using my hands, I grabbed hold of objects on the screen and moved them around. Sensors at the bottom of the screen sensed my movements.

Known as “Decommissioning Avatar," this leading-edge system, which employs virtual reality to recreate actual nuclear reactor decommissioning sites, was developed by Norway's Institute for Energy Technology (IFE).

It is used to confirm operational processes for work related to decommissioning a reactor and to investigate any associated risk in advance of carrying out actual work.

“The catalyst for development was technical cooperation with Japan," said IFE division head of software engineering, Terje Johnsen, 53. Work first began on using virtual reality technology when the institute was requested to simulate decommissioning of the Fugen advanced thermal reactor prototype located in Fukui Prefecture.

Compared to demolishing a regular building, there are a number of major differences in dismantling a nuclear power plant.

While proceeding with the dismantling, it is important to keep air conditioning and other equipment functioning right until the very end. While work progresses, wires and pipes that must be left operational need to be carefully selected from among an intricate maze of wiring and plumbing running throughout the plant.

Additionally, in order to reduce radioactive waste as much as possible, parts and rubble resulting from the dismantling must be carefully classified and sorted according to their level of contamination. To minimize exposure to workers, radiation levels at the site must be monitored and understood at all times.

Wanting “simulation technology that would ensure both safety and efficiency," the Fugen side approached Norway's IFE, with whom it already had a cooperative relationship, about developing an appropriate system.

In hindsight, Masanori Izumi, 34, who works for the Japan Atomic Energy Agency, operator of the Fugen plant, said: “At that time Japan's experience with decommissioning was minimal, we really didn't know much about it. We wanted to use virtual reality to acquire a realistic image of the work at hand."

The result was a system named VRdose. Computer graphics are used to recreate the actual site on a monitor. Avatars representing workers are made to move about the virtual site, allowing exposure doses to be calculated. It is possible to simulate a variety of movements and compare doses each time. At the time, the system was attracting global attention as a never-before-tried initiative.

Applying this technology, the IFE has created all kinds of simulation technology similar to the “Decommissioning Avatar" system.

The IFE provided a virtual reality program to the Leningrad nuclear power plant in Russia for use in the maintenance of its aging reactors. And, working cooperatively with the Norwegian army, it also built training software for dismantling retired Russian nuclear submarines. The institute is also engaged in developing software for aiding in the decommissioning of the Chernobyl nuclear power plant.

The IFE is an independent organization that is not affiliated with the government or any university.

Its mission is to develop “useful technology." István Szöke, 35, a senior researcher in software engineering at the institute, said, “Decommissioning should develop into quite a substantial business. We want to expand our range of activities going forward."

(The second part of this article was written by Norito Kunisue of GLOBE.)

The Asahi Shimbun GLOB


Partager cet article
Pour être informé des derniers articles, inscrivez vous :
Commenter cet article